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POSTED: Saturday, Aug. 30, 2008

Build a rain garden to manage wet areas

A rain garden basically copies the function of a wetland or native forest by collecting runoff moisture and absorbing, filtering and recharging the aquifer. It is an ornamental way to cope with increasing amounts of impermeable surfaces such as roads, driveways, rooftops and parking areas.

A rain garden is also a good way to manage a wet area of the garden.

If you are interested in building a rain garden, the first step is to identify the natural drainage areas of your yard. This may be an obvious low area in the yard or an area where you want runoff water to collect. There is some excavation involved because you want to dig below the subsoil for water to pond and infiltrate as well as create a natural drop in grade of usually 6 inches.

Organic soils are best for rain gardens, so once the area has been dug out, you want to mix in generous amounts of compost. Use some of the excavated soil to build a swale or slight berm and create an entry to funnel water to the rain garden.

A wide selection of native plants are suited for landscaping a rain garden. Dogwood, spirea, snowberry and evergreen huckleberry will give year-round interest and provide habitat for birds. You can also use ornamental grasses and perennials around the edge of the rain garden. Try gaura, coreopsis, echinacea and liatris.

Washington State University Extension has published a wonderful handbook on rain gardens. It details step by step the design, construction and management for optimum benefit. Rain gardens are an important design tool in protecting water quality.