How to Design and Plant a Rain Garden
A "rain garden" is somewhat like a dry creek -- it is a depression into which water flows during wet periods. And the runoff sinks into the ground to prevent stormwater runoff that carries pollutants into the street...into the gutters...and into surface water bodies such as streams, lakes and the ocean.
Here is a way to plan and plant your rain garden, with general garden size and runoff strategy provided by John Kuchinski PE, of OEST Associates in South Portland, Maine.
Calculate Rain Garden Size
Measure the Local Drainage Area and Water Volume
Find the area draining to the rain garden and measure the area of impervious (pavement, walks, roof, etc) and multiply by one inch of rainfall. Take the landscaped/lawn areas and multiply by ½ inch of rain. This will give a volume of water in cubic feet.
| ELEMENT | Measurement |
| Impervious area | Square Feet |
| ...multiply | x 1" of rainfall |
| Landscaped/Lawn area | Square Feet |
| ...multiply | x .5" rainfall |
| RESULT | Volume of Water in cubic feet |
Size the Rain Garden
Size the rain garden to contain the volume of runoff to a maximum depth of 6". To determine the depth take the average area, add the area at the top of the slope into the rain garden and bottom of the rain garden and divide by 2.
| ADD Average Area | Square Feet |
| ADD Top of Slope | Square Feet |
| ADD Bottom of Rain Garden | Square Feet |
| .......... | Divide by 2 |
| RESULT | Square Feet of Garden |
The area of the rain garden should be approximately 5 to 10 percent of the area draining to it.
Plant the garden with native or drought tolerant plants that can also tolerate occasional immersion in water.
Recommended Plants for Rain Gardens
The Brooklyn Botanic Garden provides a list of some native plants suitable for rain gardens, listed by region. They are also attractive to butterflies, birds, and other wildlife. Be sure to choose species appropriate for the degree of sun or shade on the site.
Categories of plants include Wildflowers, Ferns, Grasses, and Sedges,
Trees and Shrubs.
California
California Wildflowers, Ferns, Grasses, and Sedges
- Aquilegia formosa, Columbine
- Aralia californica, Elk clover
- Aristolochia californica, Pipevine
- Darmera peltata, Umbrella plant
- Delphinium glaucum, Tower delphinium
- Dicentra formosa, Pacific bleeding heart
- Epipactis gigantea, Stream orchid
- Lilium pardalinum, Leopard lily
- Mimulus cardinalis, Scarlet Monkeyflower
- Mimulus primuloides, Primrose monkeyflower
- Rudbeckia californica, Coneflower
- Polypodium californicum, California polypody
- Carex nudata, California black-flowering sedge
- Juncus patens, California gray rush
California Trees and Shrubs
- Calycanthus occidentalis, Western spicebush
- Corylus cornuta var. californica, Hazelnut
- Myrica californica, Wax myrtle
- hysocarpus capitatus, Ninebark
- Populus fremontii, Freemont cottonwood
- Salix lucida ssp. lasiandra, Yellow tree willow
- Ribes sanguineum, Red-flowering currant
- Rubus spectabilis, Salmonberry
- Vaccinium ovatum, California huckleberry
- Washingtonia filifera, California fan palm
N.C. Cooperative Extension has an outstanding Web site that is dedicated to all aspects of building rain gardens.
Be sure to check the The Brooklyn Botanic Garden's regional lists to find plants well suited for not only the weather patterns, but native wildlife.
Regions that benefit from specially selected plants include:
- Northeast and Middle Atlantic states and southeast Canada
- Southeast and Deep South
- South Florida
- Midwest and Great Plains states and south central Canada
- Western Mountains and Pacific Northwest
- California
- Desert Southwest
Nature's diversity is wondrous...and deserves our respect for the interdependent species that have developed adaptive colonies.
Have fun!
Edited by Carolyn Allen, owner/publisher of Solutions For Green
Publication Date:
6/27/2009
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