Rain gardens are a special type of planted area that is meant to collect and hold rainwater while letting it slowly soak into the ground. Water from roofs, gutters, driveways, and streets is diverted into a depression in the ground. The purpose of a rain garden is to reduce runoff and keep pollutants from entering our clean water systems. Gardens are filled with perennial flowers and shrubs which help to stabilize the bowl and soak up some water as well as provide food and shelter for wildlife.
The Natural Resource Conservation Service or NRCS provides insight on how to design a garden.
Location – Rain gardens must be located to intercept runoff from impervious areas. They can be placed anywhere good soils with adequate percolation rates exist. It is best to keep rain gardens away from building foundations, utilities, and septic systems.
Size – Rain gardens are typically 7 to 20 percent the size of the impervious surface generating the runoff entering the garden. Measure the square footage of the impervious area (length x width); then multiply this by 0.07 (7 percent). Determine a length and width of the rain garden that best fits the site. For example, a 2,000 sq./ft. roof, when multiplied by 10 percent, would call for a rain garden 200 sq./ft. in size, or 20′ long by 10′ wide.
Garden Depth – A typical rain garden is between six and nine inches deep. It must be level side to side and end to end, and the berm must be level so storm water runoff spreads evenly.
Soil Amendments – To prepare for a rain garden, remove 12 inches of soil to create a depressional area. Add three inches of sand, two inches of compost and one inch of topsoil, and blend uniformly.
Plant Selection – While rain gardens are a highly functional way to help protect water quality, they can also be an attractive part of your yard and neighborhood. Choose native plants based on site considerations for light, moisture, and soil. Vary plant structure, height, and flower color for seasonal appeal and butterfly habitat. Mowed grass borders or hard edging are recommended around the garden. The use of native plants is encouraged. Young plants, or plugs, are best for rain gardens because they are easier to establish and maintain. When laying plants out, randomly clump individual species in groups of 3 to 5 plants to provide bolder color. Be sure to repeat these individual groupings to create repetition and cohesion in a planting. It is a good idea to place plant labels next to each individual grouping. This will help identify the young native plants from weeds as you maintain the garden. It is important to water rain gardens regularly throughout the first season. Once established, they will thrive without additional watering. A two-inch layer of shredded wood mulch is an important part of a rain garden. Mulch helps retain moisture and discourages weed seeds from germinating.
Step By Step- Creating Your Garden
Before: Area where rain garden is needed. Located near a downspout in front yard.
MISS DIG was called to ensure no utilities were located underground.
The water flow was calculated determining the size of the garden. Area was dug creating a bowl.
Landscape fabric was laid to help reduce weeds as well as hold rocks and plants in place when water flows.
Small rocks were placed in the channel to stabilize the ground when water travels from the downspout to the garden.
A rain shower tests the holding capacity. Water should filter and drain quickly. Water from this rain event was gone in 20 minutes. Mulch was added.
More plants will be added to this garden during the fall season. Plants will be well established by spring.
If something like this would benefit your yard but you aren’t sure where to get started, contact the Clinton Conservation District. Our staff has personally constructed rain gardens. They can help you choose a location, calculate your size, and pick out the right plants.
By: Kelcie Sweeney, Executive Director
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