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Selecting Your Structure

S
       etting out to build a high tunnel   Single-bay high tunnels come in two       tunnel owners are wise to remove
       is no different from any other      primary shapes: Quonset and Gothic        their plastic for the duration of the
       capital project. The steps prior    arch (see diagram below). The             snowy season.
to construction—planning, financing        Quonset shape is relatively short and
and funding, and ordering—are often        squat with a rounded roof and sloped      Match your structure’s design load to
the most difficult. The actual building    sides, while the Gothic, like a           local conditions of snow and wind.
project is relatively simple and can be    cathedral, has a high pointed peak and    Some greenhouse suppliers can select
exciting. The completion of any            straight sidewalls. Unheated Quonset      design specifications appropriate to
project has rewards of satisfaction and    structures can also serve as cold         your county. In the first winter, one
future profit.                             frames for overwintering nursery          northern farmer’s high tunnel—
                                           stock. Multi-bay high tunnels,            purchased from a southern supplier—
In shopping for a high tunnel, and         including the Haygrove structure          was destroyed in a snowstorm, along
here we focus on single-bay                described in this manual, are usually a   with the perennial plant material
structures, a grower will need to select   series of interconnected Quonset-         inside.
from an array of designs, sizes, and       shaped tunnels. Gothic type tunnels
special features. Different materials      have several advantages compared to       The taller sidewalls of Gothic tunnels
and construction methods can also be       Quonset models. In many                   offer more usable space along the
used. Experienced farmers have             circumstances, these advantages           sides for crop production and growth
weighed the advantages and                 easily offset their greater cost.         and for working comfort. For trellised
disadvantages of these options for                                                   crops like tomatoes, Gothic-style
their climate, markets, production         A Gothic-shaped structure readily         tunnels provide adequate height both
aims, and bottom line.                     sheds snow because of the steep pitch     for the interior and perimeter rows.
                                           of its roof. Quonsets, especially those   The headroom over the edge beds in a
Quonset or Gothic-shaped                   with PVC bows, need to be swept free      Quonset tunnel may be so low that
Structures?                                of snow to prevent collapse. When         even a short person is uncomfortable
The shape of a tunnel affects its          snow threatens, some growers set up       when using a walk-behind seeder, for
performance. It will have an effect on     2" x 4"s as temporary props under the     instance.
lighting (and shading), energy gain,       ridge pole, purlins, or bows of their
growing space, and ventilation.            Quonset-shaped high tunnels. PVC          The Gothic shape also contributes to
                                                                                     better air exchange and moisture
                                                                                     control, and thus a superior growing
                                                                                     environment. The greater height of
                                                                                     Gothic tunnels allows for better
                                                                                     ventilation through higher gable-end
                                                                                     vents. Gothic arch roofs tend to have
                                                                                     enough of an angle to help shed water
                                                                                     that condenses on the interior, instead
                                                                                     of dripping on the plants below.

                                                                                     In Quonset tunnels, since the whole
                                                                                     structure is curved, opened roll-up
                                                                                     sides expose some of the crops
                                                                                     growing along the side to precipitation
                                                                                     and other adverse weather conditions.
                                                                                     This defect can be partially alleviated
                                                                                     by purchasing extended ground posts.

                                                                                     Footprint
                                                                                     High tunnels come in many sizes, in
                                                                                     widths from 14' to over 40' and in
                                                                                     incremental lengths. A width to length
                                                                                     ratio of 1:2 is ideal for passive solar

28 – High Tunnels
gain (See Mazria’s “The Passive            To get the most from your investment,       caterpillar tunnels can be constructed
Solar Energy Book”). However, you          it might make more sense to start with      of this weaker material. It should be
get more for your money with a 30' x       a short, wide house (i.e., 30' x 48') and   noted that PVC is a persistent poison
96' high tunnel than a 30' x 60'           add on later than to buy a 16' x 96'        that harms human and animal health
structure.                                 high tunnel that may quickly outgrow        and pollutes the environment during
                                           its usefulness.                             manufacture and disposal (See “The
Narrower tunnels will experience                                                       Trouble with PVC” on page 31).
more heat loss than wider tunnels          Also when determining the size of
because of their perimeter to growing      tunnel to build, take into account how      Bow spacing will depend upon the
area ratio. A 10' x 90' tunnel has a       the structure will fit on your property.    overall design of the tunnel, the
200' lineal perimeter and a 900 square     What are the site possibilities? How        anticipated snow load, and the
foot growing area, whereas a 30' x 70'     much land is available and what is its      strength and capacity of its component
tunnel also has a 200' lineal perimeter    topography? It is critical to have          steel. Although a 4' bow spacing is
and 2,100 square foot growing area.        enough room around the tunnel for           used fairly commonly, with trusses
The second structure has 133% more         easy access with vehicles and               placed on every other bow, growers
growing area, and less than half the       equipment, snow removal, water              are increasingly turning to 5' bows
ratio of perimeter (or heat loss           drainage, and ventilation; to avoid         that utilize trusses on every bow.
potential) to growing area. Wider          shading; and to allow for future
tunnels also tend to be taller and         expansion (See “Site Considerations”        (See “Bending your Own Frames” on
provide improved ventilation and           on page 26).                                page 43.)
interior air circulation.
                                                                                       Baseboards and Gable-
Under northern growing conditions,                                                     ends
even 30' wide high tunnels can be
sufficiently ventilated with roll-up       Selecting Materials                         Most high tunnels use wood for
                                                                                       baseboards, hip boards and gable-end
sides and large gable-end vents and                                                    framing. For the gable-end, another
doors. In warmer climates, in tunnels      The Frame                                   option is steel. While more costly, it
with tall, dense crops like tomatoes,      Historically, wood was commonly             will not need to be replaced and is
narrower tunnels (20' to 26') may          used to frame greenhouses, but it is        easy to work with. For the baseboard,
more effectively reduce stale air in the   has gone out of fashion because of its      recycled plastic lumber, that is rot and
middle of the structure without            relatively high maintenance cost and        insect resistant, is another
mechanical ventilation.                    the availability of steel greenhouses.      comparatively expensive alternative.
                                           Pete Johnson, a year round grower in
Size                                       North-central Vermont, is an                In selecting the type of lumber to be
How big should your high tunnel be?        exception. He is currently growing          used for the baseboard and hip board,
Consider not just how much growing         tomatoes and salad crops in a very          consider their rates of decay. Finding
space you expect to use now, but also      large high tunnel which he framed           lumber that is affordable, durable, and
what you’ll want a few years into the      with Eastern white cedar and other          sustainably harvested is a challenge
future. A well-built tunnel will last at   local trees. For most growers, steel is     and trade-offs are inevitable. For
least 20 years.                            the best material for a high tunnel         example, redwood is very expensive
                                           frame. The best greenhouse structures       and unsustainable.
Another important factor in                are made of high tensile strength steel
determining the size of high tunnel to     covered with a very good galvanized         Other more accessible choices,
purchase is the amount of additional       coating to prevent rust.                    (depending on location) include rot-
workload you are prepared to take on.                                                  resistant wood species such as the
Steve Moore estimates that a 30' x 96'     An alternative to steel for the             cedars, cypress, black locust, and
high tunnel that is intensively planted    structural members of a high tunnel is      Osage Orange. White oak can also be
with multiple crops can take 10 hours      polyvinyl chloride (PVC) pipe. Price        used, though it will need to be
or more of labor each week after           is PVC’s only real advantage                replaced after about eight years, the
initial set up and skill development.      compared to steel. Mainly it is used in     second time you replace the tunnel’s
Marketing time is additional. When a       farmer-built tunnels. Tunnels whose         polyethylene film. Cheaper but less
farm uses a simple cropping pattern,       bows are made of PVC pipe are more          attractive options are hemlock, pine,
like Slack Hollow Farm’s winter            prone to collapse under snow load and       and spruce, listed from most to least
spinach system, regular management         wind. Only narrow high tunnels with a       rot-resistant.
time can be greatly reduced.               Quonset-shape and smaller walk-in or

29 – High Tunnels
The Trouble with PVC: A Cheap but Unsustainable Material                           Due of the dangers of exposure to
                                                                                    human and animal health, CCA
 Polyvinyl chloride (a.k.a. vinyl or PVC) is a chlorinated hydrocarbon, like        (chromated copper arsenate) pressure-
 DDT and dioxin. During PVC production and disposal, very large quantities          treated wood has not been produced
 of hazardous organochlorine chemicals are produced unintentionally and             for most residential and general
 released into the environment. As a result of its intrinsic hazards, PVC is        consumer uses since 2004. Two
 under intense scrutiny in many countries, by governments as well as                Canadian government agencies,
 environmental and health advocates.                                                Environment Canada and Health and
 PVC is virtually impossible to recycle because each PVC product contains a         Welfare Canada, consider arsenic to
 unique mix of additives. Even in Europe, where PVC recycling is more               be a “non-threshold toxicant” (i.e., a
 advanced than in the U.S., less than 3% of post-consumer PVC is recycled.          substance for which there is believed
 And even most of this tiny fraction of PVC is merely “down-cycled” into            to be some chance of adverse health
 other products, so the amount of virgin PVC produced is not reduced.               effects at any level of exposure).
                                                                                    Arsenic leaches out into soil and is
 The production of chlorine for PVC uses as much energy as 80 medium-               taken up by plants. Organic farmers
 sized nuclear power plants would generate. Chlorine production is an               are prohibited from using arsenic-
 extremely energy-intensive process that consumes about 1% of the world’s           containing pressure-treated lumber.
 total electrical output.
 Among the toxic chemicals produced during the PVC lifecycle are                    Borates are one of the arsenic-free
 chlorinated dioxins, chlorinated furans, PCBs, hexachlorobenzene, and              wood treatment alternatives already
 octachlorostyrene. Workers and communities are exposed to high levels of           on the market. Treating oak with
 the toxic substances released into water, air, and soil due to PVC production.     approved borate products may
 These toxic substances are also released when PVC is incinerated.                  lengthen its lifespan to 12 years. Steve
                                                                                    Moore has treated oak with sodium
 As a group, toxic by-products of PVC production are highly persistent. These       tetraborate and sodium octaborate,
 chemicals do not degrade in nature, so they build up in the environment.           both of which may meet organic
 Transported by wind currents and water, their presence has been documented         standards if from mined sources. He
 even in the most remote regions of the globe.                                      uses these food grade borate products
 Since these chemicals are fat-soluble, they build up in the tissues of living      as they can be readily and
 organisms. In species high on the food chain (like humans), the levels of these    inexpensively obtained from local
 chemicals can be millions of times greater than in the environment. In mammals,    chemical suppliers. Borate wood
 these chemicals easily cross the placenta and concentrate in breast milk.          preservatives such as Boracare can be
                                                                                    purchased from pesticide distributors.
 Some of the toxic chemicals produced when PVC is made are dangerous                They penetrate into the wood much
 even at extremely low doses. For instance, at doses in the low parts per           more effectively than the food grade
 trillion, dioxin causes damage to fetal development, and the immune and            materials dissolved in water.
 endocrine systems, and impairs reproduction. Cancer and brain and nervous
 system damage are also associated with exposure to these organochlorines.          End walls can be made of plywood
 In its pure form, PVC is rigid and brittle. To make flexible vinyl products,       (painted is best), twin wall
 large quantities of plasticizers called “phthalates” are added. Phthalates cause   polycarbonate sheets ($1.50/ft2), other
 cancer, infertility, testicular damage, reduced sperm count, suppressed            structured sheets, or just polyethylene
 ovulation, and abnormal development of male reproductive tract in lab              film ($0.10/ft2). Of course, opaque
 animals. Like the organochlorine byproducts of PVC production, phthalates          materials like plywood prevent light
 are pollutants that bioaccumulate (i.e., persist in the environment) and are       transmission.
 found in the tissues and fluids of the human population. As they are not
 chemically bonded to PVC, but merely mixed in when the vinyl is                    Twinwall polycarbonate is an
 formulated, they eventually leach out into air, water, and other substances        extruded ribbed high-tech plastic with
 with which the vinyl comes in contact.                                             double walls for added insulation. It is
                                                                                    sold as structural sheeting. For high
 Pure PVC is not stable, so lead, cadmium, and organotins are added to
                                                                                    tunnels, it has an application for the
 stabilize vinyl used in construction and for other extended-life applications.
                                                                                    gable-end walls. As a hoop house
 These stabilizers, which are toxic and persistent in the environment, are
                                                                                    covering, it compares favorably with
 released when vinyl is formulated, used, and disposed.
                                                                                    both polyethylene and glass. It
 (Source: Thorton, PhD, Joe. Environmental Impacts of Polyvinyl Chloride            transmits up to 83% of light (more
 Building Materials. A Healthy Building Network Report.)                            than two layers of polyethylene film),

30 – High Tunnels
and insulates 40% better than glass,       unheated structures. In heated             cover inside the structure. He also
but weighs one-sixteenth as much and       structures (where the interior frost is    hoped to gain the benefit of enhanced
won’t shatter. It is very durable and      not present), infrared AC plastics         light transmission and save money by
cuts easily with a saw. It is far more     undoubtedly retain heat better.            not using another layer of high tunnel
expensive than poly but costs less                                                    covering. But neither of these theories
than glass.                                New designer greenhouse films are          proved correct. In the dead of winter,
                                           now entering the market. When the          the double walled tunnel stayed
Plastic Film                               Cramers replaced the film on their         warmer and outperformed the single
By far the most common covers for          Haygrove multi-bay tunnel, they            layered tunnel.
high tunnels of all types are made of      chose Luminance THB (thermal heat
polyethylene. UV resistant                 barrier) poly which costs 10% more         Double Versus Single
greenhouse-quality polyethylene is far     than ordinary greenhouse film (See         Layers
superior to common construction-           www.bpiagri.com/hort-luminance.htm).       A double layer of poly film with
grade polyethylene. It transmits light     Using infrared blockers, this enhanced     inflation between the layers provides
better; is more resistant to wind, heat,   poly reduces excess daytime heat and       insulation and reduces heat loss by
and yellowing; and has a longer life.      scorching while also helping to            40% according to Aldrich and Bartok
                                           minimize heat loss at night. It also       (see NRAES publication,
It is important to replace poly film as    increases light diffusion, making more     “Greenhouse Engineering,”). Along
recommended. For instance, after four      light available to plants to increase      with increasing heat retention, the
years, standard 6-mil plastic loses        photosynthesis and yields. In              second poly layer reduces the light
about 15% of its ability to transmit       particular, it is recommended for          level by about 10% so a balance must
light. This is particularly significant    ornamentals and nursery stock and has      be reached. Low light levels cause
during winter production, especially       been shown to improve tomato yields.       plants to become weak and leggy, and
in cloudy climates.                        However, the manufacturer cautions         slow down growth. As an alternative
                                           that it is not the best choice for early   to double poly layers with an inflation
Greenhouse film treated with anti-         spring growth.                             fan, some farmers use multiple layers
condensate additives prevents                                                         of floating row covers, which more
condensation drips. Infrared re-radiant    Steve Moore experimented with              drastically decrease light
(IR) materials are added to film to        several types of plastic film over a       transmission. Unless these covers are
reduce overnight heat loss. In the         multi-year period on two adjacent          removed during the day, crop
U.S., metal halides are typically used     high tunnels. He compared double           production may suffer.
to treat the film, while in Europe         layers (inflated) of the standard 6-mil
phosphorous and boron compounds            4-year film with infrared re-reflectants   Many farmers have found it sufficient
fill this function.                        and anticondensate to single layer         to use a single layer of polyethylene
                                           Coeava, a 7.8 mil film with reportedly     on their high tunnels. However, in the
Chris Wien, at Cornell University,         an 8-year useful life.                     winter, these high tunnels will have
points out that “films that lack an                                                   greater heat loss and will be colder
additive which blocks infrared             In south central Pennsylvania, a high      than tunnels with a double layer of
radiation can allow so much heat to        tunnel with two layers of 6-mil, 4-year    poly. And where a heating system is
escape on cold clear nights that           standard poly was warmer by an             used, significantly more fuel will be
temperatures in high tunnels are lower     average of over 6°F during the winter,     needed if just a single layer of poly
than they are outside the tunnel. You      and had superior plant growth              film is employed. Using a double
can have instances in which the plants     compared to high tunnels with a            layer requires electricity to run a small
inside freeze before plants just outside   single layer of 7.8 mil high               blower fan. An alternative to being
the greenhouse. It is very important       performance plastic. Steve suspects        connected to the electrical grid is a
that polyethylene films used on high       that this difference in thermal            modest solar power system. (See
tunnels have an infrared blocker           performance between the two types of       “Photovoltaic Inflation Systems” on
added to prevent such a problem.”          film would be less significant in a        page 48 and “Getting the Right Pressure
                                           warmer climate or under late fall or       on Your Inflation” on page 46.)
Anecdotal evidence suggests that the       early spring conditions.
frost forming on the inside of the                                                    Disposal and Recycling of
plastic on a high tunnel is an excellent   In carrying out this experiment, Steve     Agricultural Plastic Films
reflector of infrared radiation. Steve     had thought that the lower insulating      Plastic film must be disposed of when
Moore thinks that it may be equal in       ability of a single layer of poly could    its useful life is over, presenting the
value to special infrared AC plastic in    be offset by using more layers of row

31 – High Tunnels
farmer with a disposal problem.             at very high temperatures and are          When highly contaminated plastics
Polyethylene covers on high tunnels         equipped with mandatory pollution          are used to make the pellets, more
and greenhouses make a significant          control devices. An early 1990s study      toxic emissions result, sometimes
contribution to the growing problem         for the US EPA reported that 20 times      exceeding regulatory limits. One
of waste plastics. Polyethylene film        as much dioxin, 40 times as much           hypothesis is that dirt and debris limit
has rapidly replaced more durable           particulate matter, and many times         air movement to the combustible
materials in many farm applications.        more metal emissions resulted from         materials—a problem that increases
Plastic bags and covers are used to         open burning of household waste in         when plastic mulches are wet.
store hay and ferment animal feeds          barrels compared to municipal waste
such as silage and haylage, and             incinerators.                              Originally researchers envisioned “co-
palletized goods are shrink-wrapped.                                                   firing” small burners with these waste
Most of these plastic films are             Since that study, the gap in emissions     plastic pellets and coal for heating
produced from low-density                   from open burning versus incineration      greenhouses and for other farm
polyethylene (LDPE #4) resins.              has grown exponentially due to             applications. But pollution concerns
                                            stricter pollution control standards for   may require that the pellets be burned
The most environmentally sound              incinerators imposed since 1995.           as a tiny portion of the total mix in a
disposal option for these plastics is       Between 1990 and 2000 emissions of         large industry or municipal
recycling, which is discussed below.        toxic compounds called dioxins and         incinerator. The toxicity of ash from
Most agricultural plastics are not          furans declined by about 99% and           burning plastic fuel pellets on the
recycled, however, in part because          heavy metals by more than 90% in 66        farm is another area of concern.
recycling opportunities are few and         large municipal waste incinerators.
far between. Surveys in New York                                                       Recycling is a superior way to dispose
and Pennsylvania suggest that about         On-farm burial removes refuse from         of agricultural plastics. Recycling
half of agricultural plastics are burned    sight, but decomposition is extremely      programs are underway in the
and the remainder are buried or             slow and the potential exists for          Northeast US and Canada for
dumped on-farm. These states, like          movement of water-soluble                  handling most types of plastic resins
many others, do not restrict the on-        breakdown products into                    used in agriculture, though their
farm disposal of plastics. Therefore,       groundwater. Leaving discarded             geographic coverage is spotty. In the
farmers have no economic or legal           plastic lying around is unsightly and      absence of such a program, some
incentive to transport these materials      gives a negative impression about          farmers are stockpiling their waste
to a regional transfer station or other     agriculture. Pools of water that form      plastic film until they have access to a
central collection facility for recycling   in the plastic film serve as mosquito      recycling program. A trip to purchase
or controlled disposal (at a landfill or    breeding grounds.                          equipment or supplies may serve as an
incinerator).                                                                          occasion to bring waste plastic to a
                                            Municipal disposal in landfills or         distant recycling program.
Burning agricultural plastics in open       incineration is a better alternative for
fires or burn barrels is a burdensome       disposing of waste plastics than on-       In the Northeast, two successful
and unpleasant job. It is also highly       farm burning, burial, or non-disposal.     agricultural plastic recycling programs
polluting and carries short- and long-      Farmers often reject this option           stand out as models for government
term health risks. A chemical fact          because of the expense, time, and          initiatives and individual
sheet cautions firefighters to wear a       logistics involved.                        entrepreneurs. A polyethylene nursery
self-contained breathing apparatus                                                     film collection program was started in
where there is a risk of exposure to        Another disposal method—pelletizing        New Jersey around 1997. This state-
burning polyethylene and states that        waste agricultural plastic into fuel       run collection program collects
fumes from molten or burning                nuggets—has been under                     “clean” bundles of nursery and
polyethylene can cause respiratory          investigation by at Pennsylvania State     greenhouse films. Its Mt. Holly site
irritation, headache, and nausea.           University researchers since 1995.         accepts film from out-of-state
                                            The “densified” fuel pellets would         growers. In its first five years, with
Low temperature combustion of               generate energy when burned with           100 to 125 growers participating,
plastic film that occurs in on-farm         coal in boilers. These pellets would       almost 1.8 million pounds of nursery
burning produces soot and other             also eliminate the problem of densely      film was recycled. The $20 to $25 per
noxious emissions and also leaves           compacted plastic bales causing “hot       ton fee is substantially less that the
toxic residues. These emissions are far     spots” that damage incinerator             $60 per ton landfill tipping fee.
in excess of those released by              equipment.
municipal waste incinerators that burn

32 – High Tunnels
With an initial aim of reducing             company has installed a $10 million       easier choice for other farmers in their
farmers’ tipping fees, Lancaster            wash line to clean dirty plastics and     region.
County farmer Daniel Zook started a         also has a pick line to remove debris.
viable agricultural polyethylene                                                      This section was adapted in part from
collection business that is now             The black and white agricultural films    Levitan, Lois, and Barros, Ana.
actually paying $80 to $100 a ton for       used for mulch bags and wrapping are      “Recycling Agricultural Plastics in
waste polyethylene. In 2005 (its fifth      not much in demand by plastic             New York State.” March 11, 2003.
year), Zook Plastic Recovery sold           recyclers as the pigments must be         2nd ed. Environmental Risk Analysis
500,000 pounds of plastics. Zook set        greatly diluted to manufacture            Program. Cornell University.
up the program with Trex, a company         marketable plastic lumber. This is        http://environmentalrisk.cornell.edu/C
that reprocesses the material into          relevant to high tunnel growers           &ER/PlasticsDisposal/AgPlasticsRec
plastic lumber for decking. Besides         because, in many regions, the bulk of     ycling/. Personal communications
guaranteeing a market, this firm            agricultural film is used by dairy        with plastic recyclers and reports
guided Zook through start-up and            farms and feed producers, and             from Penn State provided additional
helped him purchase a cardboard             greenhouse film alone might not be        background.
baler. Zook holds month-long waste          abundant enough to support a
plastic collection drives each spring       collection program.
and fall and for a couple weeks in the
summer. He also accepts plastic at
other times. After he bales this plastic,
                                            Agricultural plastics are also more
                                            costly and inefficient to collect than    Multi-Bay Tunnels
he has it hauled to a Trex factory in       urban plastics, because they are
Virginia.                                   dispersed across the countryside and      Multi-bay high tunnels are a special
                                            farmers dispose of these plastics         category of tunnel. The most
A 2003 Cornell report lists several         sporadically and seasonally. Since        prominent manufacturer of this type
other agricultural plastic recycling        concentrated quantities of agricultural   of tunnel is the British company,
efforts. A plastic lumber re-processing     plastics are more attractive to           Haygrove Ltd. As fruit farmers in
facility based in Prince Edward             recycling markets, recycling programs     Herefordshire, England, Haygrove
Island, Canada, is capable of handling      may need to be organized into             found single bay tunnels inadequate
“dirty” LDPE plastics used in               regional or statewide programs.           for field-scale crop protection. With
dairying. A nationwide, industry-                                                     multi-bay tunnels in Spain as an
sponsored network collects high-            Farmers are more likely to participate    inspiration, it developed its own
density polyethylene pesticide              in recycling where there is a nearby      model.
containers. In the US and Canada, an        collection system, where burning and
industry-sponsored program based in         dumping are prohibited, and where         In Spain, where the climate is mild,
Ontario, Canada, picks up, pays for,        tipping fees for solid waste disposal     multi-bay tunnel frames can be rather
and re-processes polystyrene nursery        are significantly higher than for         weak. Haygrove tunnels improved on
flats and trays.                            recyclables. Regional and statewide       the original Spanish tunnel concept by
                                            recycling programs may be most            making them appropriate for use in
The recycling of agricultural plastics      appropriate given the capital costs for   the U.K. Since they were first
lags behind other types of recycling        recycling equipment, the sporadic and     introduced in 1996, their use has
due to several barriers. Municipal          seasonal nature of plastic removal, the   spread to 30 countries, from Norway
waste transfer stations cannot easily       dispersed feedstock for recycling, and    to Australia, and by 2006, they were
accommodate loose plastic film,             the critical mass of materials needed     protecting over 7,000 acres of crops.
which is bulky and difficult to handle.     to attract industry.
Any collection site must be equipped                                                  Like other high tunnels, Haygroves
to bale the material separately.            Despite these challenges,                 enable the farmer to extend both ends
                                            opportunities for new private and         of the growing season. They also
The quality of agricultural plastic film    public recycling efforts abound. While    prevent rain, wind, and hail damage,
is often compromised by                     greater farm use of polyethylene is       reduce pesticide use, and avoid the
contamination of dirt, moisture, or         increasing the magnitude of the           loss of harvest days due to
debris. Contamination reduces the           disposal challenge, high oil prices are   precipitation.
marketability and/or the price paid.        also creating greater demand for waste
For example, the Trex Company pays          plastics. Farmers who use agricultural    In terms of environmental
less than one-fifth its standard rate for   plastics should consider taking an        management, Haygroves vent more
plastics that require pre-cleaning. This    active role in making recycling an        fully than typical single-bay high

33 – High Tunnels
tunnels. Haygrove’s lacing system          Haygrove tunnels concentrate the run-      farmers in the Eastern U.S. to grow
holds the polyethylene cover securely      off in the leg rows between the bays,      crops in a multi-bay high tunnel. He
in place while allowing a grower to        and this water must be controlled.         grows fall raspberries, everbearing
vent the tunnels up to 8' or 10' high.     Prior to construction, most growers        strawberries, and cut flowers (for
This design feature virtually              form shallow swales that are covered       October weddings) in the structure
eliminates the problem of excess           with weed barrier cloth. The legs are      and also has five heated and unheated
tunnel heat and humidity.                  then drilled into the soil through small   single bay high tunnels.
                                           slits in the cloth.
Haygroves are three-season structures.                                                After going on the Haygrove grower
They are not designed to support a         Haygroves are sold in various bay          tour in England, he was sold on this
heavy snow load. In temperate              widths and heights to accommodate a        type of high tunnel. Based solely on
regions, the polyethylene film should      range of needs. The structures are tall    economic considerations, he opted to
be removed for the period of time          enough for tractor access and dwarf        buy a cheaper model from another
during which snowfall is possible.         tree-fruit production. The Haygrove        company (which we will refer to as
The film is “hibernated” by pulling it     design allows adjacent bays to be          “Brand X”), instead of a Haygrove,
off the hoops, down onto the Y of the      managed for different microclimates,       which it superficially resembled. He
legs, and covering it with black plastic   with curtains dividing bays with cool      purchased a four-bay structure that
that is secured with twine. This           and warm crops. The configuration of       covers a quarter acre for under
eliminates any chance of snow              these tunnels provides for easy            $7,000; each bay measured 26' x 100'.
damage to the tunnel and protects the      expansion of growing area to the sides     A Haygrove covering a third acre
film from UV exposure when not in          or ends.                                   would cost $12,000, in part because
use. At the beginning of the next                                                     the shipping is the same whether one
growing season, the film is remounted      These tunnels retail for about half the    buys an acre or a fraction of an acre.
on the hoops and secured with the          cost of traditional, single-bay high
rope lacing.                               tunnels. The minimum Haygrove              “There are many subtle differences
                                           purchase is a half-acre; however, a        that you can’t see in the catalogue,”
Haygroves can withstand relatively         full trailer load contains two acres and   says Rob, explaining his
high winds. Each Haygrove leg and          the delivery cost is the same whether      disappointment at the weaknesses of
anchor has an auger welded to it, and      the trailer is full or not.                the structure he selected. He has had
these are drilled 30" into the soil;                                                  to modify and reinforce the high
cement is not used. This keeps             Construction time is faster for these      tunnel in order for it to function.
Haygrove tunnels from lifting out of       multi-bay structures than for              Contrasting the two companies, he
the soil, something that can happen        traditional high tunnels. Typically,       characterizes Haygrove as “farmers
with single bay tunnels that are not       growers report 250 to 300 man-hours        turned metal benders” and Brand X as
cemented into the ground. During           to construct an acre-sized Haygrove        “metal benders who happen to make
high winds, Haygroves should be left       compared to 75 or 100 hours for a 30'      products for farmers.”
fully vented. This decreases pressure      x 96' tunnel (1/12th acre).
on the tunnel by allowing some of the      Construction involves relatively few       While on the tour in England, he
wind to move through the tunnel            tools and no lumber. Along with            watched how quickly the Haygrove
while still shielding the crops from its   delivery, Haygrove provides on site        went up. The Brand X structure took
full force.                                hoop bending and construction              much longer to assemble and
                                           training for customers. Since these        construction was far from smooth.
Most growers in temperate climates         tunnels follow the natural contours of     “There is no comparison,” Rob
vent (open) and close their tunnels        the land, there is no need for heavy       observes. A major difference is that
every day for the first six weeks or so    equipment to prepare a level site.         Haygroves can be constructed out of
of the season and then leave them                                                     extra-long pieces because they are
completely vented for the majority of      Inferior Multi-Bay High                    shipped from the United Kingdom in
the growing season. No special             Tunnels                                    a container and then delivered as a
attention to venting is required during    One farmer decided to buy a less           unit to the customer. Haygrove
the period when severe thunderstorms       expensive multi-bay structure to save      personnel come and bend the hoops
are most likely. Daily venting and         money, and regrets his purchase. Rob       on the farm.
closing is again practiced during the      Hastings, the owner-operator of
fall.                                      Rivermede Farm in Keene Valley,            Brand X’s multi-bay high tunnel
                                           New York (in the Adirondacks), may         consists of multiple pieces that need
                                           be one of the most Northern-most           to be bolted or screwed together. For

34 – High Tunnels
instance, there are five pieces in each   poly cover is secured to the                 vegetables, cut flowers, greens, and
Brand X hoop while a Haygrove hoop        framework with the same rope lacing          herbs.
comes as a single piece. “I had to find   system used on Haygrove’s multi-bay
a flat surface on the farm to assemble    tunnels and therefore provides
the hoops so they would not be            excellent venting. With a minimum
twisted.” Each of these joints presents   10' height at the peak, it has a large air
a weak spot, and Rob has experienced      volume for its size. Being a single-bay
a plethora of failures around these       tunnel, the Solo seals well for
joints. “I had to double screw every      maximum season extension. Like
hoop where it joins the Y post,” he       other Haygroves, it is sold as a three-
says. “It either tore out the tek screw   season structure and is not engineered
or bent them.”                            for snowload.

Rob has identified various annoying       Solos can be erected on hills or
design flaws in the Brand X. In a         uneven sites and compared to other
Haygrove the hoops rest on the Y post     single-bay tunnels, much less                The size of walk-in tunnels is
and no water can get in and freeze.       construction time is required. As with       variable. They range from 8' to 18' in
The Brand X structure allows water to     Haygrove’s multi-bay high tunnels, no        width and cover two to four beds.
enter and freeze. Haygroves have a        carpentry or extra materials are             Their length may be from 24' to 300'
peg at the top of each Y post for tying   required. While Solos are single-bay         or more, depending on the length of
the rope to that keeps the plastic film   tunnels, they can be built on double         beds they are intended to cover and
on. The Brand X lacks the peg and         prong anchors (8" between bays) to           limits to the sizes of available covers.
there is nothing to tie to.               cover large areas.                           The flexible tunnel length enables a
                                                                                       grower to construct a walk-in tunnel
The Haygrove has an effective way to      A Solo package, including the poly           virtually anywhere on the farm
finish off the end walls ands             film cover and 12 mil roll-up doors          because it can be sized to fit into a
simultaneously provide wind bracing.      for both ends, costs about $1 per            farm’s existing bed system. The
The Brand X structure comes with a        square foot, or about half the cost of a     tunnels are tall enough to walk in and
reinforced plastic end wall which has     more conventional high tunnel.               are accessed by ducking under the
not been satisfactory. “The flopping                                                   sides anywhere along their length
plastic acts like a gigantic sail tied                                                 (hence their name).
down with an anchor,” observes Rob.
He plans to do some cross bracing to
shore up the plastic.                     Walk-in Tunnels                              Bows for walk-in tunnels may be
                                                                                       made from PVC, electrical conduit, or

The lack of technical support is
                                          (Caterpillars)                               galvanized steel hoops. To erect the
                                                                                       tunnel, the bows are either slipped
another major frustration. “Brand X                                                    over ground stakes made of rebar or
barely knew I had bought one,” he         Walk-in tunnels are inexpensive              tubular steel, or the bows are set
says. “When I called, I was talking to    alternatives to the greenhouse-like          directly into the ground about a foot
someone who was clueless and who          structures that come to mind when            deep. Bows are spaced six to ten feet
was not a farmer.” Rob recommends         thinking about high tunnels. For an          apart, depending on the site’s wind
other farmers learn from his mistakes     equivalent area under cover, they cost       exposure. It is best not to construct the
and “invest in the best.” “I’m sorry I    less than a quarter of the price of a        tunnel broadside to the wind, but if
didn’t ask questions,” he concludes.      more traditional high tunnel. With           that is unavoidable, the tunnel will
                                          respect to environmental                     serve as an effective windbreak for
                                          modification, they are intermediate
Single-Bay Tunnels in the                                                              crops planted on its lea side.
                                          between traditional high tunnels and
Haygrove Style                            the low tunnels commonly used by
Haygrove’s newest product is the                                                       A 1/4'' rope tied from hoop to hoop is
                                          vegetable growers. (See “Low                 used to form a ridge purlin. The purlin
“Solo” single bay tunnel. It comes in
                                          Tunnels” on page 38.)                        is attached to heavy-duty ground
sizes appropriate for the smaller
grower. Typical dimensions are 24' x                                                   stakes at both gable ends. The
                                          Due to their segmented appearance,           structure is quite “loose” when
200' and 28' x 200'', though various
                                          some growers call these structures           uncovered; much of the tunnel’s
widths and lengths are available. This
                                          “caterpillar tunnels” (see diagram).         structural integrity comes from the
Quonset-shaped structure is built of
                                          They have been used to grow
14 gauge galvanized steel hoops. Its

35 – High Tunnels
cover and the way it is secured to the     temperatures. During the coldest           Farm Tek, “the only source of very
ground.                                    periods of the year, sections of the       long plastic” of which they are aware.
                                           sides (the cover) are propped up with      Their other walk-ins are skinned in
Walk-in tunnels may be covered with        short “Y” shaped props or branches         Typar.
greenhouse plastics, heavy spun-           cut for the purpose. When
bonded fabrics such as Typar, or           temperatures warm, the sides may be        Caterpillars have become important
shade cloth. The cover should be           rolled up along the entire length of the   on Windflower Farm because they are
matched to the intended use of the         tunnel. Clamps or tall “Y” props can       easy to construct and cover, and are
structure. The less expensive Typar        help hold the rolled up plastic in         inexpensive, while providing many of
might be the better choice, for            place. The sides must be rolled down       the benefits of a multi-bay structure
example, if the goal is to give a boost    when high winds threaten.                  like a Haygrove. Steel hoops and
(or provide insect protection) to cool-                                               plastic film for one of their 16' x 200'
season crops such as spring greens.        These tunnels are highly portable.         tunnels cost them about $1,500, about
Greenhouse plastic would be the            They may be erected and dismantled         one-third the cost of a Haygrove
better choice for an early planting of     relatively quickly. For example, two       multi-bay high tunnel. In addition, air
tomatoes. And shade cloth might be         200' long units built to cover three       flow in caterpillars is excellent—
selected for rooting strawberry tip        beds of lettuces were erected by Ted       better than in a more expensive,
cuttings.                                  and Jan Blomgren and a co-worker           conventional high tunnel—as
                                           over the course of a morning.              caterpillars open fully like a
The covering is held fast by 1/4'' ropes                                              Haygrove. (But unlike a Haygrove,
that are drawn over the top of the         One way to reduce the annual costs of      management of high winds in a
structure (Canastoga wagon-style) and      construction and dismantling is to         caterpillar requires closing the sides.)
are secured to stakes or earth anchors     leave the caterpillar tunnel in place
in the ground. These ropes give the        from year to year, and to develop a list   To get high quality fruit early from
structure its segmented, caterpillar-      of tunnel crops around which a crop        their first planting, Ted and Jan
like appearance. The edges of the          rotation plan might be developed.          transplant zucchinis and cucumbers
plastic are left loose, but the covering                                              into walk-in tunnels on May 1. These
should be sized so that there are at       Walk-ins are highly adaptable              tunnels span three beds that are six
least two feet of extra material on        structures. They may be built over         feet on center. Early harvests of both
each side. In particularly windy           existing crops, or over bare ground for    of these vegetables are important in
locations, the covering may be             a later planting. They may be built in     meeting their goal of delivering a
secured by placing rocks or small          the fall, left uncovered during the        diversity of “real vegetables” (as
sand bags on the edges of the plastic.     winter, and then covered in the spring     opposed to salad greens) to their New
At the gables ends, the plastic is         for an early planting. Or they may be      York City-based CSA membership.
bunched together using rope, and the       used to cover tomatoes during the
rope is tied to a secure stake. The        spring and summer, and then taken          Cucumbers, planted two rows per bed
tunnel’s dimensions should be              down and reconstructed over an             into black plastic (or six rows across a
configured to fit commonly available       existing fall spinach crop.                tunnel), start yielding a substantial
greenhouse films or floating row                                                      harvest by the end of June. The
covers.                                    Caterpillar Tunnels at                     zucchinis go into bare ground, with
                                           Windflower Farm                            one row running in the middle of each
While they have many advantages,           Ted and Jan Blomgren have found            of the three raised beds. Each row of
starting with their cost, walk-in          many uses for walk-in tunnels to           zucchini is sandwiched between rows
tunnels are really three-season            produce vegetables and cut flowers.        of quick Asian greens. These greens
structures. The wide bow spacing that      On Windflower Farm in Easton, New          will be harvested by the middle of
keeps them cost-effective greatly          York, they construct some of their         June just as the zucchinis are filling
reduces their snow load capacity, so       caterpillars with metal bows spaced        out the space. By the end of the first
the covering should be removed             10' apart, and others using PVC bows       week of July, the zucchini harvest is
before winter. However, walk-in            spaced 6' to 8' apart. At any given        going strong.
tunnels with a bow-to-bow spacing of       time in the growing season, the
4' and a width of 10' have reliably        Blomgrens may have as many as              On May 1, tomato transplants are
withstood snow.                            9,000 to 12,000 ft2 of walk-in tunnels     planted into three beds in walk-in
                                           on their farm, with the typical tunnel     tunnels for first harvest in July. Using
Walk-in tunnels must be ventilated         200' long. Most are covered in 6 mil       the hybrid variety ‘Mountain Spring’
manually to avoid excessive                greenhouse plastic obtained from           as their mainstay, Windflower Farm

36 – High Tunnels
gets a high quality fruit that bears well   minimum of two people to install a          pounds per plant on their 500 plants.
over a long period of time. In 2005,        plastic cover.                              (Production varies considerably
they harvested from their May 1                                                         among the diverse heirloom varieties
planting until late October. They have      On walk-in tunnels built for fall           grown at this farm.) At $3/lb. for #1
also produced eggplants and bell            lettuce and salad mix, they may still       fruit, and $2/lb. for seconds, Chris and
peppers in walk-in tunnels.                 use Typar as the cover. Ted and Jan         his wife, Tammara Van Ryn, grossed
                                            sometimes build tunnels over beds           almost $16,000 on this crop, produced
The Blomgrens initially experimented        where they have already set                 in one-eighth of an acre of caterpillar
with walk-in tunnels to protect China       transplants. Using a marking rod, they      tunnels.
asters from aster yellows, a disease        pound in stakes at 10' intervals and
transmitted by leafhoppers. The             then lower hoops over the stakes. For       Chris used 1-1/2" diameter Schedule
alfalfa fields that surround                an inside cover, they use a midweight       40 PVC pipe, rather than steel, for
Windflower Farm are leafhopper              fabric, such as 0.9 ounce Covertan,         bows. The bows are spaced every 6'
habitat. Ted says they skinned these        suspended over low wire hoops. They         and placed on rebar stakes, with a
tunnels with Typar because “We              harvest mature lettuce from these           rope and another pair of stakes in
thought we could get away without           unheated tunnels as late as                 between. His tunnels are 10' wide,
rolling up the sides,” something that       Thanksgiving. Ted cautions that this        which allows just two rows of
wouldn’t be possible for plastic-           design has no capacity to bear snow.        tomatoes per tunnel.
covered tunnels which trap heat more
effectively. “Now, tarnished plant bug      Caterpillar Tunnels at New                  Ideally, he said, the tunnel would be 2'
is our only insect problem,” says Ted.      Minglewood Farm                             wider, with a corresponding increase
                                            In 2004, Chris Lincoln grew half his        in height to accommodate the
Besides preventing aster yellows, the       tomato crop at New Minglewood               indeterminate varieties that he grows.
tunnel environment produced China           Farm in walk-in tunnels. Better yields      As it is, when the plants fill out, they
asters with stems three feet long.          and a higher percentage of #1s have         are a bit crowded and grow into the
Short-stemmed cut flowers are not           convinced him to raise his entire           sides and roof of the tunnel. The
desirable and Ted and Jan realized          tomato crop in these tunnels. This          actual size is perfect for determinate
that the extended stem length was a         year, he used four 100' long tunnels to     tomatoes, which he does not grow.
benefit that tunnels could provide          grow 800 row feet of heirloom
other cut flowers. The absence of           tomatoes for retail sale at a farmers’      Wind is the biggest threat to the walk-
wind and reduction of light in the          market and to restaurants.                  in tunnel design, but built properly,
walk-in tunnels are two factors                                                         they seem to hold up adequately.
associated with longer stems.               Chris notes higher yields, higher           Unlike a more conventional high
                                            quality, a longer harvest season, and       tunnel, where the plastic is attached
Windflower Farm currently grows             cleaner fruit as benefits of growing        directly to a steel frame, walk-in
stock, snapdragons, godetia, larkspur,      fresh market tomatoes in these              tunnel plastic is held down by ropes
Bells of Ireland, and lisianthus in         tunnels. He also counts the low cost of     secured to the earth by means of rebar
walk-in tunnels to achieve much             the tunnels and the ease of moving          stakes or earth screws. Like the
earlier blooms and longer stems. They       them to different sites on the farm as      Blomgren’s structures, Chris uses
have come to prefer walk-in tunnels to      advantages to walk-in tunnels when          ropes over top of the plastic and
regular high tunnels. They are also         compared to more permanent,                 secured to long rebar stakes driven
convinced that plastic film is superior     stationary high tunnels.                    deep into the ground. If these ropes
as a tunnel cover to Typar except for                                                   are not secure, wind can cause
mid-summer production. In the               Getting earlier tomatoes was not the        damage. To prevent wind damage, it
summer, they use Typar to protect           overriding factor in adopting this          is critical that these anchors are long
against insects, diffuse the brightness     growing environment. New                    and stout enough to hold the ropes.
of the sun, and shelter the flowers         Minglewood’s typical tomato
from wind.                                  schedule (reported for 2005) is as          Chris believes that walk-in tunnels
                                            follows: Seed on March 28, transplant       have been more time-consuming for
Though they are moving away from            on May 16, begin picking on July 23,        New Minglewood Farm than regular
Typar, Ted stresses that it has two         last harvest on October 18, first killing   hoop houses would be. This is mainly
virtues. It costs about half as much as     frost on October 21.                        due to the labor involved with setting
plastic, and its light weight makes it                                                  up and covering these tunnels before
easy to use. “I can cover a 200-foot        In 2005, they sold 5,885 pounds of          tomato planting and disassembling
tunnel myself,” he said. It takes a         tomatoes with an average of 11.8

37 – High Tunnels
them later in the year after the plants    easier field production. The O’Haras       that these plants are winter annuals.
have been removed.                         complement their low tunnels with          They have no disease and insect pests
                                           two small 14' and 16' wide high            when we grow them out of season.”
Another regular task during the spring     tunnels used for seedling production.
and fall is opening and closing the                                                   The seeding dates for their winter and
sides, depending on sun, rain, and         The couple markets their mixed             spring low tunnel crops are
temperature. To vent, Chris rolls up       vegetables and maple syrup                 astonishing late. They continue
the plastic and clips it to a rope. Once   cooperatively with Bryan’s father.         planting through the beginning of
the weather warms, the sides stay up       Their stand always sells out at the two    December and start up again in
all summer.                                Saturday farmers’ markets their            February. All these crops—which
                                           family attends from early May              include lettuces, Asian greens,
In 2006, Chris mulched with black          through Thanksgiving. The nearby           spinach, kales, Claytonia, scallions,
landscape fabric. He used a weed           Willimantic Food Co-op, which just         beets, carrots, dandelions, parsley, and
barrier fabric to accelerate tomato        tripled its store area, is their other     arugula—are direct seeded with an
development, suppress weeds, and           major outlet and has a standing order      Earthway seeder. Normally, harvest
prevent soil splash on the plants. He      with them.                                 continues until Christmas and then
chose a 6' wide fabric and covered the                                                resumes in March. The mild winter of
2' wide space between tunnels as well      Several factors, including southern        2005-06 allowed them to harvest at
as all the ground inside of the tunnels,   exposure and wind protection, help         intervals in January and February as
enabling him to locate the tomato          make low tunnels feasible for              well.
rows at the intersection of two pieces     impressive season extension at
of the fabric. This arrangement            Tobacco Road Farm. The low tunnels         At Tobacco Road Farm, beds are
eliminated the need to burn or cut         at the farm are situated on a sloping,     standardized at 3' wide, separated by
plant holes into the fabric.               southwest facing field. Conifer            8" wheel tracks. For this bed width,
                                           windbreaks mitigate the prevailing         the wire hoops must be at least 80"
                                           west wind. A third environmental           long. The hoops are about 24'' high at
                                           advantage to this site is a large          center. The minimum hoop size is
Low Tunnels: An                            damned river the size of a small lake
                                           located beyond a grove of trees next
                                                                                      3/16" round stock. Either steel or
                                                                                      galvanized will do. Wire hoops are
Alternative to High                        to the field.                              spaced 2' to 2.5' apart. The tunnels are
                                                                                      covered with two layers of plastic at
Tunnels                                    But this is not a snow-free
                                           environment. While most snowfall is
                                                                                      frost, usually in early October. In
                                                                                      March, the warming sun prompts the
In some climates, low tunnels can be       light, the O’Haras may receive as          removal of the plastic film and its
an inexpensive alternative to high         much as 8" or 10" of snow at a time.       replacement with Agribon. This spun
tunnels for cold weather season            And though snow usually melts in a         polyester row cover breathes and lets
extension. Low tunnels are simple,         few days, their low tunnels have been      water pass through. Both the plastic
protective structures consisting of        covered by snow for a month, without       and the fabric row cover are held
wire hoops covered with polyethylene       harmful effects on the plants inside.      down with up to a dozen 6 ml black
or fabric row covers. Though more          However, when the tunnels are              plastic sand bags.
labor intensive, with well-planned         covered in snow, harvest is
beds, they can be assembled with just      impossible.                                Bryan buys 20' lengths of steel wire at
a small investment.                                                                   a local metal shop and has them chop
                                           The O’Haras have been using these          it in thirds, precisely the length he
On Tobacco Road Farm in Lebanon,           inexpensive tunnels for about 10 years     needs. Bryan has used the same steel
Connecticut (about an hour east of         at an annual cost of about 7.5 cents       wire for over 10 years. Chafing from
Hartford), organic market growers          per square foot ($3,000/acre) to           surface rust only occasionally causes
Bryan and Anita O’Hara have over an        extend their growing and harvest           rips in the Agribon row cover, while
acre of low tunnels for extending fall     season. At first, their goal was to push   also helping to stick the cover onto the
vegetable production and growing a         fall production later. Driven by strong    hoops. Galvanized steel is much more
variety of baby and braising greens        customer demand for the good-tasting,      expensive.
and other vegetables throughout the        cold weather-grown greens and their
colder months. The low tunnels are         need for farm income, they just kept       For ease of operation, the beds are
removed in late spring to allow for        on expanding their off season              covered in 40' sections. Wind build up
                                           production. Bryan said, “We realized       makes longer sections unmanageable,

38 – High Tunnels
and with the length of this low tunnel,     For several years, Bryan has been         • Low tunnels allow farmers to grow
two people working together can             selecting Asian greens and arugula for      without insect and disease
uncover a whole field in little time.       cold hardiness. This breeding has           pressure.
Bryan uses two layers of cheap 1.5          yielded quick results, boosting winter    • Since low tunnels are closer to the
mil construction grade plastic. A 200'      survival from 10% to 100% in arugula        earth, they provide more heat to the
length of this film will suffice for two    just by collecting seed from planted        plants in the day. Bryan said they
40' sections. To close the ends, 50' of     that made it through the winter. For        are 3° to 5°F warmer than ambient
plastic is needed to skin 40' long low      his first breeding experiments, Bryan       temperature on cold nights, similar
tunnels. The ends are bunched up and        seeded three adjacent beds of Mizuna,       to their high tunnels.
pulled tight to create tension over the     Tatsoi, and Miruba. He replanted the      • Cold growing conditions enhance
top of the hoops.                           next year from the seed he harvested        the taste of the crops.
                                            from the Mizuna mother plants which       • Low tunnels convert readily for
Bryan is an enthusiastic missionary         successfully over-wintered. Each year       regular summer production,
for the environmental control               he collects seed from subsequent            allowing triple cropping.
provided by low tunnels. They               generations of plants interbred from      • Soil preparation and other tractor
prevent excess precipitation from           the three cultivars that survive the        operations can be carried out in the
damaging germination and ruining            winter. The hybrid seed selected from       field prior to quick installation of
crops, and protect crops from wind          a large gene pool produces very             the low tunnels.
and cold. Bryan has measured a 35°F         vigorous plants with much greater         • As they are easily removable, low
gain on sunny days. The low tunnels         cold tolerance. He can stagger seed         tunnels reduce soil salt build up.
should be vented if the outside             production by altering when he
temperature reaches about 70°F and          harvests for salad mix.                   The O’Haras also recognize that low
opened to catch precipitation if                                                      tunnels have the following
excessively dry. In 2005, Bryan kept        Chickweed is the biggest weed             disadvantages, some of which are
the beds uncovered until the                problem in winter low tunnel              common to high tunnels as well:
extremely late first frost on October       production. Before they grew year
                                                                                      • The biggest issue is that low
21, a lapse he came to regret since 20"     round, the O’Haras used to tolerate
                                                                                         tunnels are more labor intensive.
of rain that month broke all records. If    chickweed in their fields over the
                                                                                         To hoe, harvest, or irrigate, the
the beds had been covered, the crops        winter so now they are grappling with
                                                                                         coverings must be removed.
would not have been devastated and it       a huge seed bank. Seeding crops very
                                                                                      • Low tunnels cannot be automated
would have been more possible to            late in the fall allows late tillage,
                                                                                         and require a lot of bending to
control chickweed with cultivation.         reducing chickweed germination, and
                                                                                         manage the cover, causing worker
                                            the Asian greens sown on December 2
                                                                                         discomfort.
Irrigation is rarely required until later   were their cleanest over-wintered
                                                                                      • Low tunnels restrict access
in winter. The plants seem to like it       crop.
                                                                                         compared to high tunnels. One
drier in winter, Bryan explained,
                                                                                         can’t harvest on a cold, windy day.
noting two mechanisms that plants use       At Tobacco Road Farm low tunnels
to withstand cold temperatures:             have a variety of advantages:             • Cut lettuce grown under plastic
                                                                                         film-covered low tunnels (or high
desiccation and mineralization of their     • Low tunnels are very inexpensive
sap to reduce their freezing point.                                                      tunnels) is very delicate and wilts
                                               and quick to install. Bryan
These mechanisms make these crops                                                        quickly. This is one reason to
                                               estimated that two people could
extremely sweet-tasting in the winter.                                                   convert to a fabric covering like
                                               cover over an acre in two days.
                                                                                         Agribon.
                                            • In the spring, low tunnels are more
In the central Connecticut climate,                                                   • Low tunnels provide a perfect
                                               easily cooled than high tunnels to
snow build up has not been a problem                                                     environment for chickweed, the
                                               prevent bolting.
                                                                                         ultimate winter weed.
for the low tunnels. The hoops are          • Low tunnels are easily converted
pushed down by snow load, but pop                                                     • The plastic cover on low tunnels
                                               from plastic to cloth covers.
                                                                                         must be vented during warm sunny
up, pushing off the snow, as soon as        • Low tunnels allow farmers to
the sun begins melting it. Snow                                                          late fall and winter days.
                                               manage water, protecting crops and
accumulation on the wheel tracks               soil from excess rain and wind. A
insulates the low tunnels, provides a                                                 (An earlier version of this profile
                                               slight slope allows water to run off
windbreak, and also holds down the                                                    appeared in “Growing for Market.”)
                                               the tunnels.
row cover.



39 – High Tunnels

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High tunnels selectingstructure

  • 1. Selecting Your Structure S etting out to build a high tunnel Single-bay high tunnels come in two tunnel owners are wise to remove is no different from any other primary shapes: Quonset and Gothic their plastic for the duration of the capital project. The steps prior arch (see diagram below). The snowy season. to construction—planning, financing Quonset shape is relatively short and and funding, and ordering—are often squat with a rounded roof and sloped Match your structure’s design load to the most difficult. The actual building sides, while the Gothic, like a local conditions of snow and wind. project is relatively simple and can be cathedral, has a high pointed peak and Some greenhouse suppliers can select exciting. The completion of any straight sidewalls. Unheated Quonset design specifications appropriate to project has rewards of satisfaction and structures can also serve as cold your county. In the first winter, one future profit. frames for overwintering nursery northern farmer’s high tunnel— stock. Multi-bay high tunnels, purchased from a southern supplier— In shopping for a high tunnel, and including the Haygrove structure was destroyed in a snowstorm, along here we focus on single-bay described in this manual, are usually a with the perennial plant material structures, a grower will need to select series of interconnected Quonset- inside. from an array of designs, sizes, and shaped tunnels. Gothic type tunnels special features. Different materials have several advantages compared to The taller sidewalls of Gothic tunnels and construction methods can also be Quonset models. In many offer more usable space along the used. Experienced farmers have circumstances, these advantages sides for crop production and growth weighed the advantages and easily offset their greater cost. and for working comfort. For trellised disadvantages of these options for crops like tomatoes, Gothic-style their climate, markets, production A Gothic-shaped structure readily tunnels provide adequate height both aims, and bottom line. sheds snow because of the steep pitch for the interior and perimeter rows. of its roof. Quonsets, especially those The headroom over the edge beds in a Quonset or Gothic-shaped with PVC bows, need to be swept free Quonset tunnel may be so low that Structures? of snow to prevent collapse. When even a short person is uncomfortable The shape of a tunnel affects its snow threatens, some growers set up when using a walk-behind seeder, for performance. It will have an effect on 2" x 4"s as temporary props under the instance. lighting (and shading), energy gain, ridge pole, purlins, or bows of their growing space, and ventilation. Quonset-shaped high tunnels. PVC The Gothic shape also contributes to better air exchange and moisture control, and thus a superior growing environment. The greater height of Gothic tunnels allows for better ventilation through higher gable-end vents. Gothic arch roofs tend to have enough of an angle to help shed water that condenses on the interior, instead of dripping on the plants below. In Quonset tunnels, since the whole structure is curved, opened roll-up sides expose some of the crops growing along the side to precipitation and other adverse weather conditions. This defect can be partially alleviated by purchasing extended ground posts. Footprint High tunnels come in many sizes, in widths from 14' to over 40' and in incremental lengths. A width to length ratio of 1:2 is ideal for passive solar 28 – High Tunnels
  • 2. gain (See Mazria’s “The Passive To get the most from your investment, caterpillar tunnels can be constructed Solar Energy Book”). However, you it might make more sense to start with of this weaker material. It should be get more for your money with a 30' x a short, wide house (i.e., 30' x 48') and noted that PVC is a persistent poison 96' high tunnel than a 30' x 60' add on later than to buy a 16' x 96' that harms human and animal health structure. high tunnel that may quickly outgrow and pollutes the environment during its usefulness. manufacture and disposal (See “The Narrower tunnels will experience Trouble with PVC” on page 31). more heat loss than wider tunnels Also when determining the size of because of their perimeter to growing tunnel to build, take into account how Bow spacing will depend upon the area ratio. A 10' x 90' tunnel has a the structure will fit on your property. overall design of the tunnel, the 200' lineal perimeter and a 900 square What are the site possibilities? How anticipated snow load, and the foot growing area, whereas a 30' x 70' much land is available and what is its strength and capacity of its component tunnel also has a 200' lineal perimeter topography? It is critical to have steel. Although a 4' bow spacing is and 2,100 square foot growing area. enough room around the tunnel for used fairly commonly, with trusses The second structure has 133% more easy access with vehicles and placed on every other bow, growers growing area, and less than half the equipment, snow removal, water are increasingly turning to 5' bows ratio of perimeter (or heat loss drainage, and ventilation; to avoid that utilize trusses on every bow. potential) to growing area. Wider shading; and to allow for future tunnels also tend to be taller and expansion (See “Site Considerations” (See “Bending your Own Frames” on provide improved ventilation and on page 26). page 43.) interior air circulation. Baseboards and Gable- Under northern growing conditions, ends even 30' wide high tunnels can be sufficiently ventilated with roll-up Selecting Materials Most high tunnels use wood for baseboards, hip boards and gable-end sides and large gable-end vents and framing. For the gable-end, another doors. In warmer climates, in tunnels The Frame option is steel. While more costly, it with tall, dense crops like tomatoes, Historically, wood was commonly will not need to be replaced and is narrower tunnels (20' to 26') may used to frame greenhouses, but it is easy to work with. For the baseboard, more effectively reduce stale air in the has gone out of fashion because of its recycled plastic lumber, that is rot and middle of the structure without relatively high maintenance cost and insect resistant, is another mechanical ventilation. the availability of steel greenhouses. comparatively expensive alternative. Pete Johnson, a year round grower in Size North-central Vermont, is an In selecting the type of lumber to be How big should your high tunnel be? exception. He is currently growing used for the baseboard and hip board, Consider not just how much growing tomatoes and salad crops in a very consider their rates of decay. Finding space you expect to use now, but also large high tunnel which he framed lumber that is affordable, durable, and what you’ll want a few years into the with Eastern white cedar and other sustainably harvested is a challenge future. A well-built tunnel will last at local trees. For most growers, steel is and trade-offs are inevitable. For least 20 years. the best material for a high tunnel example, redwood is very expensive frame. The best greenhouse structures and unsustainable. Another important factor in are made of high tensile strength steel determining the size of high tunnel to covered with a very good galvanized Other more accessible choices, purchase is the amount of additional coating to prevent rust. (depending on location) include rot- workload you are prepared to take on. resistant wood species such as the Steve Moore estimates that a 30' x 96' An alternative to steel for the cedars, cypress, black locust, and high tunnel that is intensively planted structural members of a high tunnel is Osage Orange. White oak can also be with multiple crops can take 10 hours polyvinyl chloride (PVC) pipe. Price used, though it will need to be or more of labor each week after is PVC’s only real advantage replaced after about eight years, the initial set up and skill development. compared to steel. Mainly it is used in second time you replace the tunnel’s Marketing time is additional. When a farmer-built tunnels. Tunnels whose polyethylene film. Cheaper but less farm uses a simple cropping pattern, bows are made of PVC pipe are more attractive options are hemlock, pine, like Slack Hollow Farm’s winter prone to collapse under snow load and and spruce, listed from most to least spinach system, regular management wind. Only narrow high tunnels with a rot-resistant. time can be greatly reduced. Quonset-shape and smaller walk-in or 29 – High Tunnels
  • 3. The Trouble with PVC: A Cheap but Unsustainable Material Due of the dangers of exposure to human and animal health, CCA Polyvinyl chloride (a.k.a. vinyl or PVC) is a chlorinated hydrocarbon, like (chromated copper arsenate) pressure- DDT and dioxin. During PVC production and disposal, very large quantities treated wood has not been produced of hazardous organochlorine chemicals are produced unintentionally and for most residential and general released into the environment. As a result of its intrinsic hazards, PVC is consumer uses since 2004. Two under intense scrutiny in many countries, by governments as well as Canadian government agencies, environmental and health advocates. Environment Canada and Health and PVC is virtually impossible to recycle because each PVC product contains a Welfare Canada, consider arsenic to unique mix of additives. Even in Europe, where PVC recycling is more be a “non-threshold toxicant” (i.e., a advanced than in the U.S., less than 3% of post-consumer PVC is recycled. substance for which there is believed And even most of this tiny fraction of PVC is merely “down-cycled” into to be some chance of adverse health other products, so the amount of virgin PVC produced is not reduced. effects at any level of exposure). Arsenic leaches out into soil and is The production of chlorine for PVC uses as much energy as 80 medium- taken up by plants. Organic farmers sized nuclear power plants would generate. Chlorine production is an are prohibited from using arsenic- extremely energy-intensive process that consumes about 1% of the world’s containing pressure-treated lumber. total electrical output. Among the toxic chemicals produced during the PVC lifecycle are Borates are one of the arsenic-free chlorinated dioxins, chlorinated furans, PCBs, hexachlorobenzene, and wood treatment alternatives already octachlorostyrene. Workers and communities are exposed to high levels of on the market. Treating oak with the toxic substances released into water, air, and soil due to PVC production. approved borate products may These toxic substances are also released when PVC is incinerated. lengthen its lifespan to 12 years. Steve Moore has treated oak with sodium As a group, toxic by-products of PVC production are highly persistent. These tetraborate and sodium octaborate, chemicals do not degrade in nature, so they build up in the environment. both of which may meet organic Transported by wind currents and water, their presence has been documented standards if from mined sources. He even in the most remote regions of the globe. uses these food grade borate products Since these chemicals are fat-soluble, they build up in the tissues of living as they can be readily and organisms. In species high on the food chain (like humans), the levels of these inexpensively obtained from local chemicals can be millions of times greater than in the environment. In mammals, chemical suppliers. Borate wood these chemicals easily cross the placenta and concentrate in breast milk. preservatives such as Boracare can be purchased from pesticide distributors. Some of the toxic chemicals produced when PVC is made are dangerous They penetrate into the wood much even at extremely low doses. For instance, at doses in the low parts per more effectively than the food grade trillion, dioxin causes damage to fetal development, and the immune and materials dissolved in water. endocrine systems, and impairs reproduction. Cancer and brain and nervous system damage are also associated with exposure to these organochlorines. End walls can be made of plywood In its pure form, PVC is rigid and brittle. To make flexible vinyl products, (painted is best), twin wall large quantities of plasticizers called “phthalates” are added. Phthalates cause polycarbonate sheets ($1.50/ft2), other cancer, infertility, testicular damage, reduced sperm count, suppressed structured sheets, or just polyethylene ovulation, and abnormal development of male reproductive tract in lab film ($0.10/ft2). Of course, opaque animals. Like the organochlorine byproducts of PVC production, phthalates materials like plywood prevent light are pollutants that bioaccumulate (i.e., persist in the environment) and are transmission. found in the tissues and fluids of the human population. As they are not chemically bonded to PVC, but merely mixed in when the vinyl is Twinwall polycarbonate is an formulated, they eventually leach out into air, water, and other substances extruded ribbed high-tech plastic with with which the vinyl comes in contact. double walls for added insulation. It is sold as structural sheeting. For high Pure PVC is not stable, so lead, cadmium, and organotins are added to tunnels, it has an application for the stabilize vinyl used in construction and for other extended-life applications. gable-end walls. As a hoop house These stabilizers, which are toxic and persistent in the environment, are covering, it compares favorably with released when vinyl is formulated, used, and disposed. both polyethylene and glass. It (Source: Thorton, PhD, Joe. Environmental Impacts of Polyvinyl Chloride transmits up to 83% of light (more Building Materials. A Healthy Building Network Report.) than two layers of polyethylene film), 30 – High Tunnels
  • 4. and insulates 40% better than glass, unheated structures. In heated cover inside the structure. He also but weighs one-sixteenth as much and structures (where the interior frost is hoped to gain the benefit of enhanced won’t shatter. It is very durable and not present), infrared AC plastics light transmission and save money by cuts easily with a saw. It is far more undoubtedly retain heat better. not using another layer of high tunnel expensive than poly but costs less covering. But neither of these theories than glass. New designer greenhouse films are proved correct. In the dead of winter, now entering the market. When the the double walled tunnel stayed Plastic Film Cramers replaced the film on their warmer and outperformed the single By far the most common covers for Haygrove multi-bay tunnel, they layered tunnel. high tunnels of all types are made of chose Luminance THB (thermal heat polyethylene. UV resistant barrier) poly which costs 10% more Double Versus Single greenhouse-quality polyethylene is far than ordinary greenhouse film (See Layers superior to common construction- www.bpiagri.com/hort-luminance.htm). A double layer of poly film with grade polyethylene. It transmits light Using infrared blockers, this enhanced inflation between the layers provides better; is more resistant to wind, heat, poly reduces excess daytime heat and insulation and reduces heat loss by and yellowing; and has a longer life. scorching while also helping to 40% according to Aldrich and Bartok minimize heat loss at night. It also (see NRAES publication, It is important to replace poly film as increases light diffusion, making more “Greenhouse Engineering,”). Along recommended. For instance, after four light available to plants to increase with increasing heat retention, the years, standard 6-mil plastic loses photosynthesis and yields. In second poly layer reduces the light about 15% of its ability to transmit particular, it is recommended for level by about 10% so a balance must light. This is particularly significant ornamentals and nursery stock and has be reached. Low light levels cause during winter production, especially been shown to improve tomato yields. plants to become weak and leggy, and in cloudy climates. However, the manufacturer cautions slow down growth. As an alternative that it is not the best choice for early to double poly layers with an inflation Greenhouse film treated with anti- spring growth. fan, some farmers use multiple layers condensate additives prevents of floating row covers, which more condensation drips. Infrared re-radiant Steve Moore experimented with drastically decrease light (IR) materials are added to film to several types of plastic film over a transmission. Unless these covers are reduce overnight heat loss. In the multi-year period on two adjacent removed during the day, crop U.S., metal halides are typically used high tunnels. He compared double production may suffer. to treat the film, while in Europe layers (inflated) of the standard 6-mil phosphorous and boron compounds 4-year film with infrared re-reflectants Many farmers have found it sufficient fill this function. and anticondensate to single layer to use a single layer of polyethylene Coeava, a 7.8 mil film with reportedly on their high tunnels. However, in the Chris Wien, at Cornell University, an 8-year useful life. winter, these high tunnels will have points out that “films that lack an greater heat loss and will be colder additive which blocks infrared In south central Pennsylvania, a high than tunnels with a double layer of radiation can allow so much heat to tunnel with two layers of 6-mil, 4-year poly. And where a heating system is escape on cold clear nights that standard poly was warmer by an used, significantly more fuel will be temperatures in high tunnels are lower average of over 6°F during the winter, needed if just a single layer of poly than they are outside the tunnel. You and had superior plant growth film is employed. Using a double can have instances in which the plants compared to high tunnels with a layer requires electricity to run a small inside freeze before plants just outside single layer of 7.8 mil high blower fan. An alternative to being the greenhouse. It is very important performance plastic. Steve suspects connected to the electrical grid is a that polyethylene films used on high that this difference in thermal modest solar power system. (See tunnels have an infrared blocker performance between the two types of “Photovoltaic Inflation Systems” on added to prevent such a problem.” film would be less significant in a page 48 and “Getting the Right Pressure warmer climate or under late fall or on Your Inflation” on page 46.) Anecdotal evidence suggests that the early spring conditions. frost forming on the inside of the Disposal and Recycling of plastic on a high tunnel is an excellent In carrying out this experiment, Steve Agricultural Plastic Films reflector of infrared radiation. Steve had thought that the lower insulating Plastic film must be disposed of when Moore thinks that it may be equal in ability of a single layer of poly could its useful life is over, presenting the value to special infrared AC plastic in be offset by using more layers of row 31 – High Tunnels
  • 5. farmer with a disposal problem. at very high temperatures and are When highly contaminated plastics Polyethylene covers on high tunnels equipped with mandatory pollution are used to make the pellets, more and greenhouses make a significant control devices. An early 1990s study toxic emissions result, sometimes contribution to the growing problem for the US EPA reported that 20 times exceeding regulatory limits. One of waste plastics. Polyethylene film as much dioxin, 40 times as much hypothesis is that dirt and debris limit has rapidly replaced more durable particulate matter, and many times air movement to the combustible materials in many farm applications. more metal emissions resulted from materials—a problem that increases Plastic bags and covers are used to open burning of household waste in when plastic mulches are wet. store hay and ferment animal feeds barrels compared to municipal waste such as silage and haylage, and incinerators. Originally researchers envisioned “co- palletized goods are shrink-wrapped. firing” small burners with these waste Most of these plastic films are Since that study, the gap in emissions plastic pellets and coal for heating produced from low-density from open burning versus incineration greenhouses and for other farm polyethylene (LDPE #4) resins. has grown exponentially due to applications. But pollution concerns stricter pollution control standards for may require that the pellets be burned The most environmentally sound incinerators imposed since 1995. as a tiny portion of the total mix in a disposal option for these plastics is Between 1990 and 2000 emissions of large industry or municipal recycling, which is discussed below. toxic compounds called dioxins and incinerator. The toxicity of ash from Most agricultural plastics are not furans declined by about 99% and burning plastic fuel pellets on the recycled, however, in part because heavy metals by more than 90% in 66 farm is another area of concern. recycling opportunities are few and large municipal waste incinerators. far between. Surveys in New York Recycling is a superior way to dispose and Pennsylvania suggest that about On-farm burial removes refuse from of agricultural plastics. Recycling half of agricultural plastics are burned sight, but decomposition is extremely programs are underway in the and the remainder are buried or slow and the potential exists for Northeast US and Canada for dumped on-farm. These states, like movement of water-soluble handling most types of plastic resins many others, do not restrict the on- breakdown products into used in agriculture, though their farm disposal of plastics. Therefore, groundwater. Leaving discarded geographic coverage is spotty. In the farmers have no economic or legal plastic lying around is unsightly and absence of such a program, some incentive to transport these materials gives a negative impression about farmers are stockpiling their waste to a regional transfer station or other agriculture. Pools of water that form plastic film until they have access to a central collection facility for recycling in the plastic film serve as mosquito recycling program. A trip to purchase or controlled disposal (at a landfill or breeding grounds. equipment or supplies may serve as an incinerator). occasion to bring waste plastic to a Municipal disposal in landfills or distant recycling program. Burning agricultural plastics in open incineration is a better alternative for fires or burn barrels is a burdensome disposing of waste plastics than on- In the Northeast, two successful and unpleasant job. It is also highly farm burning, burial, or non-disposal. agricultural plastic recycling programs polluting and carries short- and long- Farmers often reject this option stand out as models for government term health risks. A chemical fact because of the expense, time, and initiatives and individual sheet cautions firefighters to wear a logistics involved. entrepreneurs. A polyethylene nursery self-contained breathing apparatus film collection program was started in where there is a risk of exposure to Another disposal method—pelletizing New Jersey around 1997. This state- burning polyethylene and states that waste agricultural plastic into fuel run collection program collects fumes from molten or burning nuggets—has been under “clean” bundles of nursery and polyethylene can cause respiratory investigation by at Pennsylvania State greenhouse films. Its Mt. Holly site irritation, headache, and nausea. University researchers since 1995. accepts film from out-of-state The “densified” fuel pellets would growers. In its first five years, with Low temperature combustion of generate energy when burned with 100 to 125 growers participating, plastic film that occurs in on-farm coal in boilers. These pellets would almost 1.8 million pounds of nursery burning produces soot and other also eliminate the problem of densely film was recycled. The $20 to $25 per noxious emissions and also leaves compacted plastic bales causing “hot ton fee is substantially less that the toxic residues. These emissions are far spots” that damage incinerator $60 per ton landfill tipping fee. in excess of those released by equipment. municipal waste incinerators that burn 32 – High Tunnels
  • 6. With an initial aim of reducing company has installed a $10 million easier choice for other farmers in their farmers’ tipping fees, Lancaster wash line to clean dirty plastics and region. County farmer Daniel Zook started a also has a pick line to remove debris. viable agricultural polyethylene This section was adapted in part from collection business that is now The black and white agricultural films Levitan, Lois, and Barros, Ana. actually paying $80 to $100 a ton for used for mulch bags and wrapping are “Recycling Agricultural Plastics in waste polyethylene. In 2005 (its fifth not much in demand by plastic New York State.” March 11, 2003. year), Zook Plastic Recovery sold recyclers as the pigments must be 2nd ed. Environmental Risk Analysis 500,000 pounds of plastics. Zook set greatly diluted to manufacture Program. Cornell University. up the program with Trex, a company marketable plastic lumber. This is http://environmentalrisk.cornell.edu/C that reprocesses the material into relevant to high tunnel growers &ER/PlasticsDisposal/AgPlasticsRec plastic lumber for decking. Besides because, in many regions, the bulk of ycling/. Personal communications guaranteeing a market, this firm agricultural film is used by dairy with plastic recyclers and reports guided Zook through start-up and farms and feed producers, and from Penn State provided additional helped him purchase a cardboard greenhouse film alone might not be background. baler. Zook holds month-long waste abundant enough to support a plastic collection drives each spring collection program. and fall and for a couple weeks in the summer. He also accepts plastic at other times. After he bales this plastic, Agricultural plastics are also more costly and inefficient to collect than Multi-Bay Tunnels he has it hauled to a Trex factory in urban plastics, because they are Virginia. dispersed across the countryside and Multi-bay high tunnels are a special farmers dispose of these plastics category of tunnel. The most A 2003 Cornell report lists several sporadically and seasonally. Since prominent manufacturer of this type other agricultural plastic recycling concentrated quantities of agricultural of tunnel is the British company, efforts. A plastic lumber re-processing plastics are more attractive to Haygrove Ltd. As fruit farmers in facility based in Prince Edward recycling markets, recycling programs Herefordshire, England, Haygrove Island, Canada, is capable of handling may need to be organized into found single bay tunnels inadequate “dirty” LDPE plastics used in regional or statewide programs. for field-scale crop protection. With dairying. A nationwide, industry- multi-bay tunnels in Spain as an sponsored network collects high- Farmers are more likely to participate inspiration, it developed its own density polyethylene pesticide in recycling where there is a nearby model. containers. In the US and Canada, an collection system, where burning and industry-sponsored program based in dumping are prohibited, and where In Spain, where the climate is mild, Ontario, Canada, picks up, pays for, tipping fees for solid waste disposal multi-bay tunnel frames can be rather and re-processes polystyrene nursery are significantly higher than for weak. Haygrove tunnels improved on flats and trays. recyclables. Regional and statewide the original Spanish tunnel concept by recycling programs may be most making them appropriate for use in The recycling of agricultural plastics appropriate given the capital costs for the U.K. Since they were first lags behind other types of recycling recycling equipment, the sporadic and introduced in 1996, their use has due to several barriers. Municipal seasonal nature of plastic removal, the spread to 30 countries, from Norway waste transfer stations cannot easily dispersed feedstock for recycling, and to Australia, and by 2006, they were accommodate loose plastic film, the critical mass of materials needed protecting over 7,000 acres of crops. which is bulky and difficult to handle. to attract industry. Any collection site must be equipped Like other high tunnels, Haygroves to bale the material separately. Despite these challenges, enable the farmer to extend both ends opportunities for new private and of the growing season. They also The quality of agricultural plastic film public recycling efforts abound. While prevent rain, wind, and hail damage, is often compromised by greater farm use of polyethylene is reduce pesticide use, and avoid the contamination of dirt, moisture, or increasing the magnitude of the loss of harvest days due to debris. Contamination reduces the disposal challenge, high oil prices are precipitation. marketability and/or the price paid. also creating greater demand for waste For example, the Trex Company pays plastics. Farmers who use agricultural In terms of environmental less than one-fifth its standard rate for plastics should consider taking an management, Haygroves vent more plastics that require pre-cleaning. This active role in making recycling an fully than typical single-bay high 33 – High Tunnels
  • 7. tunnels. Haygrove’s lacing system Haygrove tunnels concentrate the run- farmers in the Eastern U.S. to grow holds the polyethylene cover securely off in the leg rows between the bays, crops in a multi-bay high tunnel. He in place while allowing a grower to and this water must be controlled. grows fall raspberries, everbearing vent the tunnels up to 8' or 10' high. Prior to construction, most growers strawberries, and cut flowers (for This design feature virtually form shallow swales that are covered October weddings) in the structure eliminates the problem of excess with weed barrier cloth. The legs are and also has five heated and unheated tunnel heat and humidity. then drilled into the soil through small single bay high tunnels. slits in the cloth. Haygroves are three-season structures. After going on the Haygrove grower They are not designed to support a Haygroves are sold in various bay tour in England, he was sold on this heavy snow load. In temperate widths and heights to accommodate a type of high tunnel. Based solely on regions, the polyethylene film should range of needs. The structures are tall economic considerations, he opted to be removed for the period of time enough for tractor access and dwarf buy a cheaper model from another during which snowfall is possible. tree-fruit production. The Haygrove company (which we will refer to as The film is “hibernated” by pulling it design allows adjacent bays to be “Brand X”), instead of a Haygrove, off the hoops, down onto the Y of the managed for different microclimates, which it superficially resembled. He legs, and covering it with black plastic with curtains dividing bays with cool purchased a four-bay structure that that is secured with twine. This and warm crops. The configuration of covers a quarter acre for under eliminates any chance of snow these tunnels provides for easy $7,000; each bay measured 26' x 100'. damage to the tunnel and protects the expansion of growing area to the sides A Haygrove covering a third acre film from UV exposure when not in or ends. would cost $12,000, in part because use. At the beginning of the next the shipping is the same whether one growing season, the film is remounted These tunnels retail for about half the buys an acre or a fraction of an acre. on the hoops and secured with the cost of traditional, single-bay high rope lacing. tunnels. The minimum Haygrove “There are many subtle differences purchase is a half-acre; however, a that you can’t see in the catalogue,” Haygroves can withstand relatively full trailer load contains two acres and says Rob, explaining his high winds. Each Haygrove leg and the delivery cost is the same whether disappointment at the weaknesses of anchor has an auger welded to it, and the trailer is full or not. the structure he selected. He has had these are drilled 30" into the soil; to modify and reinforce the high cement is not used. This keeps Construction time is faster for these tunnel in order for it to function. Haygrove tunnels from lifting out of multi-bay structures than for Contrasting the two companies, he the soil, something that can happen traditional high tunnels. Typically, characterizes Haygrove as “farmers with single bay tunnels that are not growers report 250 to 300 man-hours turned metal benders” and Brand X as cemented into the ground. During to construct an acre-sized Haygrove “metal benders who happen to make high winds, Haygroves should be left compared to 75 or 100 hours for a 30' products for farmers.” fully vented. This decreases pressure x 96' tunnel (1/12th acre). on the tunnel by allowing some of the Construction involves relatively few While on the tour in England, he wind to move through the tunnel tools and no lumber. Along with watched how quickly the Haygrove while still shielding the crops from its delivery, Haygrove provides on site went up. The Brand X structure took full force. hoop bending and construction much longer to assemble and training for customers. Since these construction was far from smooth. Most growers in temperate climates tunnels follow the natural contours of “There is no comparison,” Rob vent (open) and close their tunnels the land, there is no need for heavy observes. A major difference is that every day for the first six weeks or so equipment to prepare a level site. Haygroves can be constructed out of of the season and then leave them extra-long pieces because they are completely vented for the majority of Inferior Multi-Bay High shipped from the United Kingdom in the growing season. No special Tunnels a container and then delivered as a attention to venting is required during One farmer decided to buy a less unit to the customer. Haygrove the period when severe thunderstorms expensive multi-bay structure to save personnel come and bend the hoops are most likely. Daily venting and money, and regrets his purchase. Rob on the farm. closing is again practiced during the Hastings, the owner-operator of fall. Rivermede Farm in Keene Valley, Brand X’s multi-bay high tunnel New York (in the Adirondacks), may consists of multiple pieces that need be one of the most Northern-most to be bolted or screwed together. For 34 – High Tunnels
  • 8. instance, there are five pieces in each poly cover is secured to the vegetables, cut flowers, greens, and Brand X hoop while a Haygrove hoop framework with the same rope lacing herbs. comes as a single piece. “I had to find system used on Haygrove’s multi-bay a flat surface on the farm to assemble tunnels and therefore provides the hoops so they would not be excellent venting. With a minimum twisted.” Each of these joints presents 10' height at the peak, it has a large air a weak spot, and Rob has experienced volume for its size. Being a single-bay a plethora of failures around these tunnel, the Solo seals well for joints. “I had to double screw every maximum season extension. Like hoop where it joins the Y post,” he other Haygroves, it is sold as a three- says. “It either tore out the tek screw season structure and is not engineered or bent them.” for snowload. Rob has identified various annoying Solos can be erected on hills or design flaws in the Brand X. In a uneven sites and compared to other Haygrove the hoops rest on the Y post single-bay tunnels, much less The size of walk-in tunnels is and no water can get in and freeze. construction time is required. As with variable. They range from 8' to 18' in The Brand X structure allows water to Haygrove’s multi-bay high tunnels, no width and cover two to four beds. enter and freeze. Haygroves have a carpentry or extra materials are Their length may be from 24' to 300' peg at the top of each Y post for tying required. While Solos are single-bay or more, depending on the length of the rope to that keeps the plastic film tunnels, they can be built on double beds they are intended to cover and on. The Brand X lacks the peg and prong anchors (8" between bays) to limits to the sizes of available covers. there is nothing to tie to. cover large areas. The flexible tunnel length enables a grower to construct a walk-in tunnel The Haygrove has an effective way to A Solo package, including the poly virtually anywhere on the farm finish off the end walls ands film cover and 12 mil roll-up doors because it can be sized to fit into a simultaneously provide wind bracing. for both ends, costs about $1 per farm’s existing bed system. The The Brand X structure comes with a square foot, or about half the cost of a tunnels are tall enough to walk in and reinforced plastic end wall which has more conventional high tunnel. are accessed by ducking under the not been satisfactory. “The flopping sides anywhere along their length plastic acts like a gigantic sail tied (hence their name). down with an anchor,” observes Rob. He plans to do some cross bracing to shore up the plastic. Walk-in Tunnels Bows for walk-in tunnels may be made from PVC, electrical conduit, or The lack of technical support is (Caterpillars) galvanized steel hoops. To erect the tunnel, the bows are either slipped another major frustration. “Brand X over ground stakes made of rebar or barely knew I had bought one,” he Walk-in tunnels are inexpensive tubular steel, or the bows are set says. “When I called, I was talking to alternatives to the greenhouse-like directly into the ground about a foot someone who was clueless and who structures that come to mind when deep. Bows are spaced six to ten feet was not a farmer.” Rob recommends thinking about high tunnels. For an apart, depending on the site’s wind other farmers learn from his mistakes equivalent area under cover, they cost exposure. It is best not to construct the and “invest in the best.” “I’m sorry I less than a quarter of the price of a tunnel broadside to the wind, but if didn’t ask questions,” he concludes. more traditional high tunnel. With that is unavoidable, the tunnel will respect to environmental serve as an effective windbreak for modification, they are intermediate Single-Bay Tunnels in the crops planted on its lea side. between traditional high tunnels and Haygrove Style the low tunnels commonly used by Haygrove’s newest product is the A 1/4'' rope tied from hoop to hoop is vegetable growers. (See “Low used to form a ridge purlin. The purlin “Solo” single bay tunnel. It comes in Tunnels” on page 38.) is attached to heavy-duty ground sizes appropriate for the smaller grower. Typical dimensions are 24' x stakes at both gable ends. The Due to their segmented appearance, structure is quite “loose” when 200' and 28' x 200'', though various some growers call these structures uncovered; much of the tunnel’s widths and lengths are available. This “caterpillar tunnels” (see diagram). structural integrity comes from the Quonset-shaped structure is built of They have been used to grow 14 gauge galvanized steel hoops. Its 35 – High Tunnels
  • 9. cover and the way it is secured to the temperatures. During the coldest Farm Tek, “the only source of very ground. periods of the year, sections of the long plastic” of which they are aware. sides (the cover) are propped up with Their other walk-ins are skinned in Walk-in tunnels may be covered with short “Y” shaped props or branches Typar. greenhouse plastics, heavy spun- cut for the purpose. When bonded fabrics such as Typar, or temperatures warm, the sides may be Caterpillars have become important shade cloth. The cover should be rolled up along the entire length of the on Windflower Farm because they are matched to the intended use of the tunnel. Clamps or tall “Y” props can easy to construct and cover, and are structure. The less expensive Typar help hold the rolled up plastic in inexpensive, while providing many of might be the better choice, for place. The sides must be rolled down the benefits of a multi-bay structure example, if the goal is to give a boost when high winds threaten. like a Haygrove. Steel hoops and (or provide insect protection) to cool- plastic film for one of their 16' x 200' season crops such as spring greens. These tunnels are highly portable. tunnels cost them about $1,500, about Greenhouse plastic would be the They may be erected and dismantled one-third the cost of a Haygrove better choice for an early planting of relatively quickly. For example, two multi-bay high tunnel. In addition, air tomatoes. And shade cloth might be 200' long units built to cover three flow in caterpillars is excellent— selected for rooting strawberry tip beds of lettuces were erected by Ted better than in a more expensive, cuttings. and Jan Blomgren and a co-worker conventional high tunnel—as over the course of a morning. caterpillars open fully like a The covering is held fast by 1/4'' ropes Haygrove. (But unlike a Haygrove, that are drawn over the top of the One way to reduce the annual costs of management of high winds in a structure (Canastoga wagon-style) and construction and dismantling is to caterpillar requires closing the sides.) are secured to stakes or earth anchors leave the caterpillar tunnel in place in the ground. These ropes give the from year to year, and to develop a list To get high quality fruit early from structure its segmented, caterpillar- of tunnel crops around which a crop their first planting, Ted and Jan like appearance. The edges of the rotation plan might be developed. transplant zucchinis and cucumbers plastic are left loose, but the covering into walk-in tunnels on May 1. These should be sized so that there are at Walk-ins are highly adaptable tunnels span three beds that are six least two feet of extra material on structures. They may be built over feet on center. Early harvests of both each side. In particularly windy existing crops, or over bare ground for of these vegetables are important in locations, the covering may be a later planting. They may be built in meeting their goal of delivering a secured by placing rocks or small the fall, left uncovered during the diversity of “real vegetables” (as sand bags on the edges of the plastic. winter, and then covered in the spring opposed to salad greens) to their New At the gables ends, the plastic is for an early planting. Or they may be York City-based CSA membership. bunched together using rope, and the used to cover tomatoes during the rope is tied to a secure stake. The spring and summer, and then taken Cucumbers, planted two rows per bed tunnel’s dimensions should be down and reconstructed over an into black plastic (or six rows across a configured to fit commonly available existing fall spinach crop. tunnel), start yielding a substantial greenhouse films or floating row harvest by the end of June. The covers. Caterpillar Tunnels at zucchinis go into bare ground, with Windflower Farm one row running in the middle of each While they have many advantages, Ted and Jan Blomgren have found of the three raised beds. Each row of starting with their cost, walk-in many uses for walk-in tunnels to zucchini is sandwiched between rows tunnels are really three-season produce vegetables and cut flowers. of quick Asian greens. These greens structures. The wide bow spacing that On Windflower Farm in Easton, New will be harvested by the middle of keeps them cost-effective greatly York, they construct some of their June just as the zucchinis are filling reduces their snow load capacity, so caterpillars with metal bows spaced out the space. By the end of the first the covering should be removed 10' apart, and others using PVC bows week of July, the zucchini harvest is before winter. However, walk-in spaced 6' to 8' apart. At any given going strong. tunnels with a bow-to-bow spacing of time in the growing season, the 4' and a width of 10' have reliably Blomgrens may have as many as On May 1, tomato transplants are withstood snow. 9,000 to 12,000 ft2 of walk-in tunnels planted into three beds in walk-in on their farm, with the typical tunnel tunnels for first harvest in July. Using Walk-in tunnels must be ventilated 200' long. Most are covered in 6 mil the hybrid variety ‘Mountain Spring’ manually to avoid excessive greenhouse plastic obtained from as their mainstay, Windflower Farm 36 – High Tunnels
  • 10. gets a high quality fruit that bears well minimum of two people to install a pounds per plant on their 500 plants. over a long period of time. In 2005, plastic cover. (Production varies considerably they harvested from their May 1 among the diverse heirloom varieties planting until late October. They have On walk-in tunnels built for fall grown at this farm.) At $3/lb. for #1 also produced eggplants and bell lettuce and salad mix, they may still fruit, and $2/lb. for seconds, Chris and peppers in walk-in tunnels. use Typar as the cover. Ted and Jan his wife, Tammara Van Ryn, grossed sometimes build tunnels over beds almost $16,000 on this crop, produced The Blomgrens initially experimented where they have already set in one-eighth of an acre of caterpillar with walk-in tunnels to protect China transplants. Using a marking rod, they tunnels. asters from aster yellows, a disease pound in stakes at 10' intervals and transmitted by leafhoppers. The then lower hoops over the stakes. For Chris used 1-1/2" diameter Schedule alfalfa fields that surround an inside cover, they use a midweight 40 PVC pipe, rather than steel, for Windflower Farm are leafhopper fabric, such as 0.9 ounce Covertan, bows. The bows are spaced every 6' habitat. Ted says they skinned these suspended over low wire hoops. They and placed on rebar stakes, with a tunnels with Typar because “We harvest mature lettuce from these rope and another pair of stakes in thought we could get away without unheated tunnels as late as between. His tunnels are 10' wide, rolling up the sides,” something that Thanksgiving. Ted cautions that this which allows just two rows of wouldn’t be possible for plastic- design has no capacity to bear snow. tomatoes per tunnel. covered tunnels which trap heat more effectively. “Now, tarnished plant bug Caterpillar Tunnels at New Ideally, he said, the tunnel would be 2' is our only insect problem,” says Ted. Minglewood Farm wider, with a corresponding increase In 2004, Chris Lincoln grew half his in height to accommodate the Besides preventing aster yellows, the tomato crop at New Minglewood indeterminate varieties that he grows. tunnel environment produced China Farm in walk-in tunnels. Better yields As it is, when the plants fill out, they asters with stems three feet long. and a higher percentage of #1s have are a bit crowded and grow into the Short-stemmed cut flowers are not convinced him to raise his entire sides and roof of the tunnel. The desirable and Ted and Jan realized tomato crop in these tunnels. This actual size is perfect for determinate that the extended stem length was a year, he used four 100' long tunnels to tomatoes, which he does not grow. benefit that tunnels could provide grow 800 row feet of heirloom other cut flowers. The absence of tomatoes for retail sale at a farmers’ Wind is the biggest threat to the walk- wind and reduction of light in the market and to restaurants. in tunnel design, but built properly, walk-in tunnels are two factors they seem to hold up adequately. associated with longer stems. Chris notes higher yields, higher Unlike a more conventional high quality, a longer harvest season, and tunnel, where the plastic is attached Windflower Farm currently grows cleaner fruit as benefits of growing directly to a steel frame, walk-in stock, snapdragons, godetia, larkspur, fresh market tomatoes in these tunnel plastic is held down by ropes Bells of Ireland, and lisianthus in tunnels. He also counts the low cost of secured to the earth by means of rebar walk-in tunnels to achieve much the tunnels and the ease of moving stakes or earth screws. Like the earlier blooms and longer stems. They them to different sites on the farm as Blomgren’s structures, Chris uses have come to prefer walk-in tunnels to advantages to walk-in tunnels when ropes over top of the plastic and regular high tunnels. They are also compared to more permanent, secured to long rebar stakes driven convinced that plastic film is superior stationary high tunnels. deep into the ground. If these ropes as a tunnel cover to Typar except for are not secure, wind can cause mid-summer production. In the Getting earlier tomatoes was not the damage. To prevent wind damage, it summer, they use Typar to protect overriding factor in adopting this is critical that these anchors are long against insects, diffuse the brightness growing environment. New and stout enough to hold the ropes. of the sun, and shelter the flowers Minglewood’s typical tomato from wind. schedule (reported for 2005) is as Chris believes that walk-in tunnels follows: Seed on March 28, transplant have been more time-consuming for Though they are moving away from on May 16, begin picking on July 23, New Minglewood Farm than regular Typar, Ted stresses that it has two last harvest on October 18, first killing hoop houses would be. This is mainly virtues. It costs about half as much as frost on October 21. due to the labor involved with setting plastic, and its light weight makes it up and covering these tunnels before easy to use. “I can cover a 200-foot In 2005, they sold 5,885 pounds of tomato planting and disassembling tunnel myself,” he said. It takes a tomatoes with an average of 11.8 37 – High Tunnels
  • 11. them later in the year after the plants easier field production. The O’Haras that these plants are winter annuals. have been removed. complement their low tunnels with They have no disease and insect pests two small 14' and 16' wide high when we grow them out of season.” Another regular task during the spring tunnels used for seedling production. and fall is opening and closing the The seeding dates for their winter and sides, depending on sun, rain, and The couple markets their mixed spring low tunnel crops are temperature. To vent, Chris rolls up vegetables and maple syrup astonishing late. They continue the plastic and clips it to a rope. Once cooperatively with Bryan’s father. planting through the beginning of the weather warms, the sides stay up Their stand always sells out at the two December and start up again in all summer. Saturday farmers’ markets their February. All these crops—which family attends from early May include lettuces, Asian greens, In 2006, Chris mulched with black through Thanksgiving. The nearby spinach, kales, Claytonia, scallions, landscape fabric. He used a weed Willimantic Food Co-op, which just beets, carrots, dandelions, parsley, and barrier fabric to accelerate tomato tripled its store area, is their other arugula—are direct seeded with an development, suppress weeds, and major outlet and has a standing order Earthway seeder. Normally, harvest prevent soil splash on the plants. He with them. continues until Christmas and then chose a 6' wide fabric and covered the resumes in March. The mild winter of 2' wide space between tunnels as well Several factors, including southern 2005-06 allowed them to harvest at as all the ground inside of the tunnels, exposure and wind protection, help intervals in January and February as enabling him to locate the tomato make low tunnels feasible for well. rows at the intersection of two pieces impressive season extension at of the fabric. This arrangement Tobacco Road Farm. The low tunnels At Tobacco Road Farm, beds are eliminated the need to burn or cut at the farm are situated on a sloping, standardized at 3' wide, separated by plant holes into the fabric. southwest facing field. Conifer 8" wheel tracks. For this bed width, windbreaks mitigate the prevailing the wire hoops must be at least 80" west wind. A third environmental long. The hoops are about 24'' high at advantage to this site is a large center. The minimum hoop size is Low Tunnels: An damned river the size of a small lake located beyond a grove of trees next 3/16" round stock. Either steel or galvanized will do. Wire hoops are Alternative to High to the field. spaced 2' to 2.5' apart. The tunnels are covered with two layers of plastic at Tunnels But this is not a snow-free environment. While most snowfall is frost, usually in early October. In March, the warming sun prompts the In some climates, low tunnels can be light, the O’Haras may receive as removal of the plastic film and its an inexpensive alternative to high much as 8" or 10" of snow at a time. replacement with Agribon. This spun tunnels for cold weather season And though snow usually melts in a polyester row cover breathes and lets extension. Low tunnels are simple, few days, their low tunnels have been water pass through. Both the plastic protective structures consisting of covered by snow for a month, without and the fabric row cover are held wire hoops covered with polyethylene harmful effects on the plants inside. down with up to a dozen 6 ml black or fabric row covers. Though more However, when the tunnels are plastic sand bags. labor intensive, with well-planned covered in snow, harvest is beds, they can be assembled with just impossible. Bryan buys 20' lengths of steel wire at a small investment. a local metal shop and has them chop The O’Haras have been using these it in thirds, precisely the length he On Tobacco Road Farm in Lebanon, inexpensive tunnels for about 10 years needs. Bryan has used the same steel Connecticut (about an hour east of at an annual cost of about 7.5 cents wire for over 10 years. Chafing from Hartford), organic market growers per square foot ($3,000/acre) to surface rust only occasionally causes Bryan and Anita O’Hara have over an extend their growing and harvest rips in the Agribon row cover, while acre of low tunnels for extending fall season. At first, their goal was to push also helping to stick the cover onto the vegetable production and growing a fall production later. Driven by strong hoops. Galvanized steel is much more variety of baby and braising greens customer demand for the good-tasting, expensive. and other vegetables throughout the cold weather-grown greens and their colder months. The low tunnels are need for farm income, they just kept For ease of operation, the beds are removed in late spring to allow for on expanding their off season covered in 40' sections. Wind build up production. Bryan said, “We realized makes longer sections unmanageable, 38 – High Tunnels
  • 12. and with the length of this low tunnel, For several years, Bryan has been • Low tunnels allow farmers to grow two people working together can selecting Asian greens and arugula for without insect and disease uncover a whole field in little time. cold hardiness. This breeding has pressure. Bryan uses two layers of cheap 1.5 yielded quick results, boosting winter • Since low tunnels are closer to the mil construction grade plastic. A 200' survival from 10% to 100% in arugula earth, they provide more heat to the length of this film will suffice for two just by collecting seed from planted plants in the day. Bryan said they 40' sections. To close the ends, 50' of that made it through the winter. For are 3° to 5°F warmer than ambient plastic is needed to skin 40' long low his first breeding experiments, Bryan temperature on cold nights, similar tunnels. The ends are bunched up and seeded three adjacent beds of Mizuna, to their high tunnels. pulled tight to create tension over the Tatsoi, and Miruba. He replanted the • Cold growing conditions enhance top of the hoops. next year from the seed he harvested the taste of the crops. from the Mizuna mother plants which • Low tunnels convert readily for Bryan is an enthusiastic missionary successfully over-wintered. Each year regular summer production, for the environmental control he collects seed from subsequent allowing triple cropping. provided by low tunnels. They generations of plants interbred from • Soil preparation and other tractor prevent excess precipitation from the three cultivars that survive the operations can be carried out in the damaging germination and ruining winter. The hybrid seed selected from field prior to quick installation of crops, and protect crops from wind a large gene pool produces very the low tunnels. and cold. Bryan has measured a 35°F vigorous plants with much greater • As they are easily removable, low gain on sunny days. The low tunnels cold tolerance. He can stagger seed tunnels reduce soil salt build up. should be vented if the outside production by altering when he temperature reaches about 70°F and harvests for salad mix. The O’Haras also recognize that low opened to catch precipitation if tunnels have the following excessively dry. In 2005, Bryan kept Chickweed is the biggest weed disadvantages, some of which are the beds uncovered until the problem in winter low tunnel common to high tunnels as well: extremely late first frost on October production. Before they grew year • The biggest issue is that low 21, a lapse he came to regret since 20" round, the O’Haras used to tolerate tunnels are more labor intensive. of rain that month broke all records. If chickweed in their fields over the To hoe, harvest, or irrigate, the the beds had been covered, the crops winter so now they are grappling with coverings must be removed. would not have been devastated and it a huge seed bank. Seeding crops very • Low tunnels cannot be automated would have been more possible to late in the fall allows late tillage, and require a lot of bending to control chickweed with cultivation. reducing chickweed germination, and manage the cover, causing worker the Asian greens sown on December 2 discomfort. Irrigation is rarely required until later were their cleanest over-wintered • Low tunnels restrict access in winter. The plants seem to like it crop. compared to high tunnels. One drier in winter, Bryan explained, can’t harvest on a cold, windy day. noting two mechanisms that plants use At Tobacco Road Farm low tunnels to withstand cold temperatures: have a variety of advantages: • Cut lettuce grown under plastic film-covered low tunnels (or high desiccation and mineralization of their • Low tunnels are very inexpensive sap to reduce their freezing point. tunnels) is very delicate and wilts and quick to install. Bryan These mechanisms make these crops quickly. This is one reason to estimated that two people could extremely sweet-tasting in the winter. convert to a fabric covering like cover over an acre in two days. Agribon. • In the spring, low tunnels are more In the central Connecticut climate, • Low tunnels provide a perfect easily cooled than high tunnels to snow build up has not been a problem environment for chickweed, the prevent bolting. ultimate winter weed. for the low tunnels. The hoops are • Low tunnels are easily converted pushed down by snow load, but pop • The plastic cover on low tunnels from plastic to cloth covers. must be vented during warm sunny up, pushing off the snow, as soon as • Low tunnels allow farmers to the sun begins melting it. Snow late fall and winter days. manage water, protecting crops and accumulation on the wheel tracks soil from excess rain and wind. A insulates the low tunnels, provides a (An earlier version of this profile slight slope allows water to run off windbreak, and also holds down the appeared in “Growing for Market.”) the tunnels. row cover. 39 – High Tunnels