How to Build a Rain Garden

1. OA Afield
How to Build a Rain Garden
Stormwater runoff is a leading cause of pollution in our drain excess water, you have a rain garden. Think of it as a
streams and lakes. Impervious surfaces all around us— mini wetland. It can fill your backyard or be as small as a
driveways, roads, parking lots—block water from draining baby pool. It can beautify your home and invite birds, but-
into the ground. Lawns are not much better, unless they terflies, and beneficial insects, including those that eat mos-
have a place where the water can go. quitoes. What’s more, it’s a manageable project that can be
Enter the rain garden. Anytime you have a dip in the built in a weekend.
landscape that contains vegetation to help soak up and Here’s how.
1. Pick the location 2. Map out the garden 3. Prepare the pit
Choose a site at least 10 feet from Make the length about twice the Start digging the first section at the
the house, on a gentle slope (less than width of the space; a kidney or uphill side until you’ve reached the
12 percent grade) that can catch water teardrop shape works well. Position it depth you want. A typical depth is 4
from downspouts. Pick a spot with full so that the longer side faces uphill to to 8 inches below the string; a flat-
or partial sun, not under a tree. Don’t catch as much water as possible. ter slope requires less depth. Repeat
place the garden where water pools Use a string to outline the perime- with each section. Once the pit is
already; the drainage needs to be good. ter of the garden.Then, use stakes dug, use a carpenter’s level to make
Silty and sandy soils drain better than and string to divide the garden into sure it’s even.
clay.To test drainage, dig a 6-inch deep sections. Do this by pounding stakes Next, begin filling the pit.You’ll
hole and fill it with water. If it takes more along the perimeter, tying one end of need enough soil to fill it close
than 24 hours for the water to soak in, string to the uphill stake where it enough to the string to leave room
the drainage is not adequate.The average meets the ground, and the other end for the plants. Start by using the soil
size of a rain garden is 100–300 square to the corresponding downhill stake you already dug out. Get extra soil if
feet.The poorer the drainage, the larger so that the string is level. Repeat so you need it. Be sure to save some soil
the garden should be. that the strings create 5-foot-wide for the next step—creating a berm.
strips across the garden.This enables 4. Make a berm 5. Plant your garden
you dig a uniformly level pit.
To keep water from flowing out of Use a variety of native wildflowers, tems. Eventually, the plants should pro-
the rain garden before it can drain, pile grasses, and shrubs. Choose combina- vide a strong underground root matrix.
up soil around the outer edge to create tions with alternating heights, bloom Lay out plants one foot apart with
a berm. Do this on only three sides of times, and textures. Pick plants for the species grouped in clumps. Dig each
the pit; leave the uphill end open to deeper end of the garden that can tol- hole twice as wide as the plant plug.
receive water.The berm should have erate more water. Don’t plant wild- The crown of the plant should be
gently sloping sides and should be tallest flower seeds directly; they don’t do level with the ground. Apply mulch
on the downhill end. Compact the berm well, and weeds tend to come up. over the bed.Water frequently until
so it won’t erode. Plant grass on it or Select plants from nurseries (not from the plants are established. Later on, no
cover it with mulch. the wild) that have established root sys- watering will be necessary.
Stakes and string help you
create a level garden.
berm
Place garden at least 10 feet from downspout. Dig out this part to 4- to 8-inch depth
create a level pit.
original slope
More info?
To learn more about this project, visit www.iwla.org/oa.
ILLUSTRATIONS BY MARIA RABINKY
12 OUTDOOR AMERICA WINTER 2006
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