Composting

1. Composting ❂ 6
G
ardeners have long made and used compost to
improve garden soil. Today, we also compost plant
and vegetable matter because it is an important way
to reduce the amount of waste that is burned or dumped in
❂ Topics in this chapter
landfills. Yard wastes and kitchen scraps can make up 20 ❂❂ The science of composting
percent or more of household garbage. Composting effec- ❂❂ Managing the decay process
tively recycles that waste.
❂❂ How to make compost
Some people think that composting is not possible in
Alaska because of the cold temperatures and the short ❂❂ Health and safety questions
growing season. Of course, that is not the case. Decom- ❂❂ Using compost
position occurs naturally in Alaska forests with organisms ❂❂ Composting food wastes
adapted to colder temperature. In Alaska, gardeners can ❂❂ Composting and the
speed up the composting process by following the same sci- environment
entific principles that are used in other parts of the country.
Composting is the science of controlling the decomposition
process.
There are two types of composting: aerobic and anaero-
bic. The organisms responsible for aerobic decay require
oxygen or a well-aerated pile. Aerobic decay happens
quickly and generates heat. The temperatures are high
enough to kill weed seeds and pathogens. Many nutrients
are retained in the compost produced. Anaerobic compost-
ing is done by organisms that do not require oxygen to live.
It is a slow process, smells bad and nutrients are lost to
the atmosphere as gas. Thus, the goal of the gardener is to
focus on the aerobic method. By Craig G. Cogger, Extension Soil Scientist,
Washington State University; Dan M. Sullivan,
Extension Soil Scientist, Oregon State University;
and James A. Kropf, Extension Agent, Pierce and
King Counties, Washington State University.
Adapted by Michele Hébert, Extension Faculty,
Agriculture and Horticulture, Cooperative
Extension Service, University of Alaska Fairbanks.

2. 114 • Composting—Chapter 6
It is broken down into carbon dioxide and
The science of composting water and releases nutrients to plants in the
process.
The cycle of growth and decay
Composting carries out part of the earth’s Fast (hot) composting
biological cycle of growth and decay. Plants The decay process can be manipulated or
grow by capturing energy from the sun, controlled to make it proceed quickly. The
See Chapter 3,
Soils and
carbon dioxide from the air, and nutrients key is to balance food, water and air in the
Fertilizers. and water from the soil. When plants, and compost pile to favor the growth of thermo-
animals that eat them die, they become raw philic (heat-loving) microorganisms. These
materials for the composting process. In organisms are the bacteria. The by-product
other words, once dead, organisms decay or of microbial activity is heat. When condi-
decompose. tions are favorable for high-temperature
Microorganisms, fungi, insects, worms, microorganisms, compost piles heat rapidly
mites and other creatures (Figure 1) convert to 120° to 150°F. The high temperature kills
the carbon from dead plants into energy for most weed seeds and pathogens (disease
their own growth, releasing carbon diox- organisms). Once the hot phase is complete,
ide into the air (Figure 2). Similarly, they lower-temperature microorganisms, worms,
recycle nutrients from decaying plants into insects and other invertebrates complete the
their own bodies and eventually back into decay process.
the soil. Other plants and microorganisms
use the carbon and nutrients released by the Slow (cold) composting
composting process, and the cycle begins If you do not maintain ideal conditions
again. for hot composting, microorganisms still
The material that remains from the decay break down wastes. Decay is slower, cooler
process is humus, a form of soil organic and less effective at killing weed seeds and
matter. It holds water and nutrients in the pathogens.
soil and makes the soil more porous and
easier to dig. Once in the soil, humus is fur-
ther decomposed by soil microorganisms. Managing the decay process
You can affect the speed of the compost
process and the quality of finished product
by managing the environmental factors.
These include the raw material or food,
moisture, air and organisms. The compost
pile can be thought of as food and home for
Actinomycetes Fungi Bacteria microbes. The management goal is to make
the conditions in the compost pile ideal for
Figure 1.—Primary groups of microorganisms the growth of microbes.
involved in composting (magnified more than
1,000 times). (Reprinted by permission from On-
Farm Composting Handbook, NRAES-54, Natural
Food (raw materials)
Resource, Agriculture and Engineering Service, For fast composting the initial mix must
Cooperative Extension, 1992: 607-255-7654; www. provide a rich food (energy) source for
nraes.org.)

3. Chapter 6—Composting • 115
Organic matter
(including carbon, Water Heat CO2
chemical energy,
protein, nitrogen)
Minerals (including
nitrogen and other
nutrients) Organic matter
(including carbon,
chemical energy,
Water Compost pile nitrogen, protein, hu-
mus), minerals, water,
microorganisms
Microorganisms
Raw materials Finished compost
O2
Figure 2.—The composting process. The amounts of carbon, chemical energy, protein and water in the
finished compost are less than in the raw materials. The finished compost has more humus. The volume of the
finished compost is 50 percent or less of the volume of raw material. (Reprinted by permission from On-Farm
Composting Handbook, NRAES-54, Natural Resource, Agriculture, and Engineering Service, Cooperative
Extension, 1992:607-255-7654; www.nraes.org.)
the bacteria. Table 1 shows some materi- alfalfa hay and deciduous leaves. These
als commonly used in making compost. materials are handy for ensuring the success
They are separated into energy materials of hot compost piles.
(nitrogen sources), bulking agents (carbon Mixing bulking agents with energy sourc-
sources) and balanced materials. es provides the right balance of moisture, air
Energy materials provide the nitrogen and nutrients for rapid composting. A mix-
and high-energy carbon compounds needed ture of one part energy source with two parts
for fast microbial growth. If piled without bulking agent (by volume) usually gives a
bulking agents, these materials usually are reasonable mix for rapid composting.
too wet and dense to allow much air into
the compost pile. When you open the pile, it Particle size
will have a foul, “rotten egg” smell. The smaller the particles size the more
Bulking agents are dry, porous materials surface area for microbial activity and the
that help aerate the compost pile. They are quicker the raw material will be able to
too low in moisture and nutrients to decay decay. Grinding, cutting, smashing or chop-
quickly on their own. ping raw materials reduces particle size. Hot
Balanced raw materials have both energy composting requires a relatively uniform
and bulking agent properties. These materi- particle size of ⅛ to ½ inch in diameter.
als compost readily without being blended Small particles do limit the amount of
with other ingredients. Examples include air that can be moved into a pile. Bulking
horse manure mixed with bedding, spoiled agents are added to increase air movement.

4. 116 • Composting—Chapter 6
High carbon material such as wood chips squeeze water out of it with your hands. At
can be screened out of finished compost dry times of the year, you may need to add
and be reused several times to increase air water. In rainy winter locations, a pile may
movement. not heat up unless you cover it to keep out
rain.
Mixing
Contrary to popular opinion, layering is Aeration
not the best way to build a pile. If all of the The microorganisms responsible for fast
materials are on hand when you build the decomposition need oxygen. The pile needs
pile, mix them thoroughly throughout the to be porous enough to pull in outside air
pile. If materials accumulate over time, add to replenish oxygen as it is used. Including
new materials to the center of the pile. This bulking agents in the mix creates a porous
practice helps aerate the center of the pile, pile. As the pile decomposes, it will settle,
where anaerobic conditions are likely to reducing aeration. Turning the pile or add-
occur. ing more bulking agents improves aeration.
Pile size Microorganisms
The pile must be big enough to hold heat. Raw materials used to form a compost
A hot pile decays much faster than a cold pile usually contain all the microorganisms
pile. Small piles usually are colder because needed to make compost. You do not need
they have small cores that hold less heat. to add soil or compost starters with special
Small piles also dry out faster. A pile of microorganisms. The best source of micro-
about 1 cubic yard is big enough for com- organisms (if needed) is finished compost.
posting, even in Alaska.
Nutrients
Moisture Just like people, microorganisms need
All materials in the pile must be moist but nutrients (such as nitrogen, phosphorus
not soaking wet. Check moisture when you and sulfur) to grow and reproduce. These
turn the pile. The mixed material should nutrients occur in the raw materials used in
feel moist, but you should not be able to the compost mix. Additional fertilizer from
any source (organic or inorganic) usually is
not needed.
How to make compost
You do not need a bin or other container
to make compost. Piles work well. How-
ever, some people prefer containers because
they look neater, or because it is easier to
shield them from pests. Containers can be
simple or fancy. Make them from materials
such as old pallets, lumber, mesh fencing or
cinder blocks (Figure 3).

5. Chapter 6—Composting • 117
Slow (cold) composting
Employing slow composting is an easy
and convenient way to turn yard wastes into
a useful soil amendment. It often is the best
method for people who do not have the time
to tend a hot compost pile. Simply mix non- Figure 3.—Some people compost in open piles; others prefer using
woody yard wastes into a pile and let them bins.
sit for a year or so. Microorganisms, insects,
earthworms and other decomposers will
slowly break down the wastes. A mixture of One option is to bury vegetable and
energy materials and bulking agents pro- fruit wastes directly in your garden. Dig a
vides the best food source and environment hole or trench about a foot deep, add a few
for decomposition (see Table 1). inches of wastes, mix them with the soil
Add fresh wastes by opening the pile, and refill the trench with soil. Another way
placing the wastes in the center and cover- to avoid pests is to compost fruit and veg-
ing them. This helps aerate the pile and also etable wastes in a worm bin (described later
buries the fresh wastes so they do not attract in this chapter).
pests such as flies, dogs and bears. Slow composting does not produce the
Fruit and vegetable wastes are particu- heat needed to kill many weed seeds. It is
larly appealing to pests, so be sure to bury best to pull and compost weeds before they
these wastes within the pile. If pests are still go to seed. If you put seeds in the compost
a problem, you may need to screen the pile pile, be prepared for more weeding.
or use another method of composting these
wastes. Fast (hot) composting
If you create and maintain a balance of
air, moisture and energy for compost mi-
Table 1.—Compost raw materials.
croorganisms, they produce a hot pile that
Energy materials
(High moisture, low porosity, high nitrogen)
breaks down quickly. The heat kills many
Grass clippings weed seeds and disease organisms. Making
Fresh dairy, chicken or rabbit manure hot compost takes extra effort, but it pro-
Fruit and vegetable waste duces a high-quality product quickly.
Garden trimmings
One method for making hot compost is
Bulking agents described below.
(Low moisture, high porosity, low nitrogen, high
carbon) Building the pile
Wood chips 1. Collect enough material to make a pile
Sawdust
Grass hay at least 1 cubic yard in volume. (An
Wheat straw open pile 5 feet wide at the base by 3
Balanced raw materials
feet high holds about a cubic yard.)
(Low to medium moisture, medium porosity, Use roughly two parts bulking agent to
medium nitrogen and carbon) one part energy material (see Table 1).
Horse manure and bedding Chop, shred, mow or smash coarse ma-
Deciduous leaves
Legume hay
terials so they will break down faster.

6. 118 • Composting—Chapter 6
Health and safety questions
Are there any plant materials to keep out The amount of turning and monitoring re-
of a compost pile? quired is difficult for even the most avid
If you are composting by the slow home composter. The simplest way to
method, keep diseased plants and seed avoid potential pathogen problems is to
heads of weeds out of your compost keep manure out of your compost pile.
pile. For any compost, avoid coarse, If you do use manure, avoid applying
woody materials because they break the compost where you grow high-risk
down slowly and make the pile hard to crops such as lettuce or carrots. Careful
turn. washing or peeling does remove most
Some plants contain compounds that pathogens. Thorough cooking is even
slow microbial decay. Western red cedar, more effective at killing pathogens.
often used for fence posts because of Keep dog, cat and pig manure out of
its resistance to decay, can break down your compost pile and garden. Some of
slowly in compost piles. the parasites found in these manures can
Can a compost pile catch fire? survive even the most thorough compost-
A compost pile will ignite only if it ing process and remain infectious for
has a very hot zone next to a dry zone. people.
Fires do not start in moist or small piles. Are herbicides a problem in compost?
Can I use manure in my compost? Some people are concerned
If you use fresh manure in a slow that herbicides (weed kill-
compost pile or directly in your garden, ers) in compost-amended soil See Chapter 20,
a small risk exists that disease-causing might harm plants. Most her- Weed
pathogens will contaminate garden bicides in home compost piles Management.
vegetables. The risk is greatest come from lawn clippings.
for root crops (such as carrots The warm temperatures in a compost pile
and radishes) or leaf crops (such accelerate herbicide breakdown to non-
as lettuce), since the edible part toxic compounds. Binding with organic
touches the soil and often is not matter in the compost also inactivates
cooked. herbicides. Breakdown and binding
You can’t be assured that reduce the risk of herbicide damage. To
pathogens are killed unless you avoid herbicide problems:
carefully monitor temperatures • Use few (or no) herbicides.
in your compost pile. To ensure • Return treated grass clippings to the
pathogen kill, the pile must lawn rather than composting them.
reach temperatures greater • Use herbicides that break down
than 130°F and must be quickly.
turned often. Turning the pile • Let your compost sit for a year or
moves cooler material from more before using it to allow nearly
the edges into the hot center. complete breakdown of herbicides.

7. Chapter 6—Composting • 119
2. Start the pile by adding energy mate- What if hot compost isn’t hot?
rial and bulking agent. Then mix with a If your pile isn’t hot, do the following:
pitchfork. • If the pile is dry, add more moisture.
3. Squeeze a handful of the mixed material • If the pile is mostly bulking agent, add
to check its moisture level. If you can energy materials or nitrogen fertilizer.
barely squeeze out a drop of water, the • If the pile is too wet, add more bulking
moisture level is ideal. If the pile is too agent. Cover the pile or build a larger
dry, add water and check the moisture pile during the rainy season.
again. If it is too wet, mix in some drier • If the pile has a foul smell, try turning
material. it more often or adding more bulking
4. Continue adding energy material and agent to increase the amount of air.
bulking agent, mixing and checking • If the pile is too small, try building a
moisture until the pile is built. larger pile to hold heat better.
Turning the pile Sometimes you may have several prob-
Use a pitchfork to turn the pile weekly, lems to overcome. If you cannot get the pile
and add water when needed. Turning gets air to heat, all is not lost. The pile eventually
into the center of the pile and speeds decay. will break down by the slow method.
It also mixes material from the outside of the
pile into the hot center. Cover the pile during Using compost
rainy periods so it will not get too wet.
The best part about compost is the ben-
Curing efit it provides your garden. Mix compost
After initial mixing, a regu- with soil to add organic matter, or use it as
larly turned pile usually stays mulch.
hot (120° to 150°F) for several See Chapter 3,
weeks. It will shrink to about Soils and Amending soil
half its original volume by the Fertilizers. Well-decomposed, earthy composts are
end of this time. good soil amendments. They make soil
The pile then needs to sit another 4 to 8 easier to work and create a better medium
weeks to cure. Curing affects the availabil- for plant growth. You can mix 1 to 2 inches
ity of nitrogen and the microbial activity of of compost into your soil before you plant a
the compost. Uncured compost may harm vegetable garden, lawn, flower bed or cover
some plants, especially when compost is crop.
used in potting soil or to start seeds. Curing
is less critical when small amounts of com- Mulching
post are worked into soil. With two compost Composts applied to the soil surface
piles, you can let one batch cure while you help control weeds, conserve water and
start another batch in the second pile. protect soil from erosion. The best time to
Temperatures during curing are 80° to apply compost mulches is in early sum-
110°F. The compost is ready to use when at mer, after plants are established and the
least 8 weeks have passed since initial mix- soil has warmed. Later, the mulch can be
ing, the pile no longer heats when turned dug or tilled into the soil. When mulching
and the material looks dark and crumbly. perennial plantings, choose compost made

8. 120 • Composting—Chapter 6
from woody bulking agents; it decomposes ded in 1-inch-wide strips and mixed with
slowly, resists compaction and slows weed peat moss make excellent bedding. Worms
establishment. need some grit for breaking down their food.
Add a little topsoil for this purpose. Put the
worms in the bedding with their first feeding.
Composting food waste
Moisture
Composting kitchen scraps in an outdoor
In order to survive, worms require 75 to
bin sometimes attracts pests. Some people
90 percent moisture content in both their
prefer using worm composting, as described
bodies and their bedding. To achieve this
below.
percentage, add 3 pounds of water for each
Worm bins pound of dry bedding (a ratio of 3:1). An
easy way to check the moisture content of
Many food wastes can be composted in bedding is to squeeze some in your hand.
worm bins. Examples include fruit (not cit- If a few drops of moisture are released by
rus) and vegetable peels, grains, pasta, baked squeezing, the bedding is sufficiently moist.
goods, coffee grounds and even coffee filters. If five or more drops are produced, the bed-
Do not add meat or dairy products. ding probably is too wet.
Place worm bins where temperature
and moisture can be controlled. An ideal Kinds of worms to use
temperature range for worms is from 55° The red worm used in a box environment
to 77°F. Worms also need a moist envi- is Eisenia foetida. These red worms feed on
ronment. Air circulation is a must in and the surface of organic matter.
around a worm box. Choose a location that Nightcrawlers and other garden earth-
is convenient for maintaining the box. worms are very important for soil improve-
The size depends on how much waste ment, but won’t survive in a worm box.
you generate per week. A box measuring 1 Earthworms live only in furrows in the soil.
foot by 2 feet by 3 feet can handle 6 pounds Number of worms
of kitchen waste per week, which is about The number of worms required depends
average for a family of four to six. on the daily weight of food waste added.
Since worms can eat their own weight in
Starting a worm bin
food in 24 hours, measure worms by weight
Colored rubber containers are popular as
rather than number. Two pounds of worms
worm bins because they are lightweight.
are needed for each pound of kitchen waste
Worms avoid light, so the container should
added per day (a ratio of 2:1). For example,
be dark inside and have a good lid. The lid
if you produce 3½ pounds of kitchen waste
should cover the top but does not need to at-
per week (½ pound per day), use 1 pound of
tach securely to the container. There should
worms. Calculate as follows:
be air holes somewhere on the container —
3½ lb kitchen waste per week
either on the lid or sides. If you use a plastic
÷ 7 days in a week
bin, be sure to add both drainage and aera-
= ½ lb waste per day (average)
tion holes. Never use a container that has
½ lb waste per day x 2 lb of worms for
been used for storing toxic chemicals.
each lb of daily waste
Start by putting bedding in the worm box.
= 1 lb of worms
Corrugated cardboard and newspaper shred-

9. Chapter 6—Composting • 121
Red worm sources for a longer time, make arrangements with
Check with your local Extension office or someone to feed your worms.
the Internet. Changing the bedding
Worm bin management After many weeks, you will notice that
the bedding is disappearing as worms and
Adding waste microorganisms decompose the material.
It is a good practice to vary the location The color of the bedding also becomes
where you bury wastes in the worm box. darker. As these things happen, the favor-
A worm box 2 feet by 2 feet has approxi- able environment for the worms decreases.
mately nine locations where you can bury Large amounts of accumulated castings
kitchen wastes. That gives you nine feed- might become harmful to the worms, since
ings before you have to bury again at the castings of one worm are toxic to other
first location. worms. Decide when to change the bedding
Grinding is not necessary because kitchen based on the condition of the bedding and
wastes break down very quickly. Do pulver- the quantity of worms in the box.
ize egg shells, however.
Population control
Leaving the box untended Worms multiply fast. Avoid overpopula-
If you need to be away from home, just tion. Use extra worms to start a new worm
feed the worms a little extra and leave box or give them to someone else who is
them undisturbed. They can go 3 weeks or starting a worm composting box.
a month without feeding. If you go away
Commonly asked questions about worms
Can a worm see? ingests the food along with a grinding
No, worms don’t have eyes. However, material such as sand, topsoil, or lime-
they are very sensitive to light, and they try stone. Contractions from muscles in the
to hide as soon as they are exposed to light. gizzard compress the particles against
Where is the worm’s mouth?
each other, thus mixing them with fluid
The worm’s mouth is in the first ante- and grinding them into smaller pieces.
rior segment. There is a small protruding Do worms need air?
lip just over the mouth. When the worm Worms need a constant supply of
is foraging, this lip stretches out to sense oxygen from the air. The oxygen diffuses
food. across the moist tissue of their skin, from
Does a worm have teeth?
the region of greater oxygen concentra-
Worms have no teeth for chewing their tion (air) to that of lower concentration
food. They grind food in their gizzard by (inside the worm).
muscle action. How do I use worm compost?
How does a worm grind his food?
Use worm compost like any other
A worm can take only a small particle compost. Sterilizing is not necessary.
of soft, moistened food in its mouth. It

10. 122 • Composting—Chapter 6
Odor and pest control
Control odors by not overloading the box
For more information
with waste, keeping out inappropriate waste
and providing adequate fresh bedding. Do UAF Cooperative Extension
not fill the bin with a lot of food waste until publications
the worm population is established. Never Composting with Worms, HGA-01020.
add cheese or other animal products to any Composting in Coastal Alaska, HGA-
type of composting system. 01021.
Fruit flies are more of a nuisance than The Compost Heap in Alaska, HGA-01022.
a serious problem. Minimize fruit flies in Worms in a Tote, HGA-01025.
a worm bin by completely covering fresh
food waste with several inches of bedding Other publications
and by covering the bedding with a sheet of Rangarajan, A., E.A. Bihn, R.B. Gravani,
newspaper, cardboard or plastic tucked in D.L. Scott and M.P. Pitts. 2000. Food
around the edges. Safety Begins on the Farm: A Grower’s
Guide. Cornell Good Agricultural Prac-
tices Program, Cornell University Col-
Composting and the lege of Agriculture and Life Sciences.
environment
Backyard composting reduces the flow of
wastes to landfills or burn piles and pro-
duces valuable organic matter for the soil at
the same time. The composting process is
fueled by the solar energy captured in plant
tissue. The benefits are the same whether
you compost in carefully tended hot piles
or in neglected slow piles. Backyard com-
posting is a simple, yet important, way to
improve our communities and the environ-
ment.