How to design and build your rain garden

1. Lecture Notes
How to Design and Build Your Rain Garden
1. Storm Water Run Off Evaluation
o Sketch the property
o Wait for rain
 not at the beginning of a storm
 not during the first storm after a dry spell
o Walk the property
 record run off observations
 note high and low spots
 downspouts, impervious surfaces, steep terrain, etc.
2. Determine a location
o What do you want to do?
 roof run off
 lawn run off
 driveway, walkway or patio run off
o Do you wan the garden in a different location?
 underground pipes
 swales
o Other factors to consider
 10 feet down hill of the building
 beyond the drip line of a tree
 away from septic systems and utilities
 avoid steep slopes
 avoid areas that don’t drain
 soil type‐ sand, silt, clay
o The garden MUST drain.
o Infiltration test
 test hole 6‐12 inches wide and 12 inches deep
 add water
 refill if dry season
 look for complete drainage in 24‐48 hours
 amending the soil
 add organic matter such as compost, humus, well rotted
manure
 sand‐ use only coarse builders’ sand not fine play sand
3. Size the garden
o Storm water calculation
 1 inch of rain on a 1000 square foot roof yields 623 gallons of
water
 multiply the footprint of your roof by .623 to find run off in
gallons for a 1 inch rain storm
 calculate average annual run off by multiplying the above
number by 42 which is the average yearly rainfall in this region
o Size must make sense in your landscape!

2.
4. Shape the garden
o Bowl shaped bottom
o Flat bottom
5. Site preparation and garden installation
o Pennsylvania One Call System 8‐1‐1 or 1‐800‐242‐1776
 It’s free and quick
o Mark your design
o Remove the turf
o Dig out the garden
o Amend the soil if necessary
o Create the berm using the removed soil
o Berm will be higher on the down slope side of the garden
o Cover the berm to prevent erosion
o Lay out the plants
o Plant
o Water the plants
o Apply 2‐3 inches of mulch
o Line any swales with rocks or stones
6. Plant selection
o Multiple zones
 wet zone‐ deepest, wettest area
 middle zone‐ holds water but drains sooner
 transition zone‐ upper zone, closest to rest of yard
 berm‐ dry
o Refer to PennState Extension plant list at
http://extension.psu.edu/gardening/maescapes/rain‐
gardens/plants‐rain‐gardens
o Match cultural requirements
 sun/shade
 moisture
 size at maturity
o Four season interest such as berries, fruits, pods, etc.
o Use native plants
 beauty
 ease of maintenance
 wildlife habitat and food source
 deep root zones
7. Maintenance
o Moisture to help establish the garden
o 1, 3, 5 Rule until the garden is established
o Check the berm for stabilization
o Check the mulch for flotation movement
o Weed as necessary