A rain garden is a depression filled with native plants that protects water quality by retaining and filtering stormwater. Rain gardens look like a normal garden, but they are designed as much for their function as their beauty.
Size: The ideal size of a rain garden is related to the size of the area that drains into the garden. For example, a home downspout often captures one-fourth of the rooftop runoff. If the downspout is directed into the rain garden, the garden must be large enough to capture and process the right amount of water. The ideal size of the garden will depend on the size of the roof. Available space and budget also come into play. Most home rain gardens range from 100 to 300 square feet, but a smaller rain garden can still filter an impressive percentage of runoff.
Location: A rain garden should be located at least 10 feet away from the building’s foundation. The bed of the rain garden must be level to allow the water to pool and soak into the earth, so it will be easiest to dig the bed on flat or gently sloping land. Don’t place the rain garden over a septic system or in areas where water already collects. Do place the rain garden where one can enjoy its colors, scents and visiting birds and butterflies.
Soil: Get to know the dirt. Sand, silt or clay? What is present will affect the preparation of a rain garden. Adding sand, organic matter and sometimes gravel will improve the drainage, especially for clay and densely compacted soil. If there is a lot of clay in the soil, consider a different site.
Plants: Go native. Native species offer a huge variety of blooms and textures, and they are naturally suited to the wet and dry extremes of a local setting. They can also go without fertilizers and pesticides, which add to the water quality problems that a rain garden is designed to address.
Advice is easy to find—browsing through it will help to save time and make smart decisions. The guides listed here include advice on site selection, size and soil, as well as plant lists and garden designs:
- “Rain Gardens: A Landscape Tool to Improve Water Quality,” from the Virginia Department of Forestry at www.dof.virginia.gov/rfb/rain-gardens.shtml or 434-977-6555.
- “Rain Gardens: A How-To Manual for Homeowners,” from the University of Wisconsin Extension at clean-water.uwex.edu/pubs/home.htm#rain
Local environmental agencies and watershed associations may also have a range of resources, such as publications, websites, presentations and even nearby rain gardens to visit.
Developers and planners can find more technical information in resources for bioretention and low-impact development. Useful websites include: