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Environmental Commission
Rain Gardens
Posted: August 14, 2009
Rain gardens were first developed in the early 1990s in Maryland by a developer interested in maintaining the natural land depressions on his construction site and putting them to work for him by capturing and infiltrating the increased amount of storm water runoff generated by constructing homes and roads. Sound complicated? It can really be quite easy and is an effective tool for you the homeowner to enhance water quality and control the storm water coming off your property.Take advantage of what nature has to offer you by capturing the rain and putting it to work on your lawn and garden areas by controlling runoff leaving your property, reducing localized flooding, increasing infiltration and planting native plants that increase biodiversity. Unlike a traditional garden a rain garden is dug down and planted slightly below grade in a basin. This enables the garden to capture and infiltrate precipitation into the ground water. No need to worry about mosquitoes an effective rain garden will infiltrate water in one to two days and won’t allow mosquitoes to breed. Rain gardens are also great in public spaces providing areas of interest while infiltrating runoff from roofs and sidewalks.
Now is a good time of year to begin planning for your rain garden. Take a walk around your lawn. Do you notice any depressions or wet spots? Are the re areas where water is creating soil erosion or ponds and puddles after rainfall events? These are all excellent spots for rain gardens. An important thing to keep in mind - Rain gardens may be located near a drainpipe from a building’s roof (with or without rain barrels) but if there’s a basement, it is important to direct the rainwater to a location at least 30 feet away from the building.
Before you begin construction of your rain garden it is important to have your soil tested by your local agricultural extension agent. To find your agent you can contact Also keep in mind how you will capture the water in your rain garden. The water should spread itself evenly over the entire surface of the rain garden and not pool in areas. During very large storms the water will overflow and should be directed towards grassy areas, wooded areas or existing storm drains. For it to be effective in infiltrating storm water a typical rain garden should range from 100 to 300 square feet. Constructed perpendicular to the slope, a rain garden should be twice as long as it is wide. The depth (or how far you need to dig to - make the base of your rain garden level) should be between four to eight inches deep. Remember that no matter what the depth, it is important to keep the garden level. Also consider the soil particle size. Is your soil sandy silty or clayey? Sand has the fastest infiltration rate and clay has the slowest. Rain gardens in clayey soil must be bigger than those in sandy or silty soil because of clays slow rate of infiltration.
There is a lot of good free information to help you plan your rain garden. An excellent resource is the Rain Garden Manual for New Jersey put out by the Native plant Society of New Jersey. This step by step guide gives you all the information you need to plan and build a rain garden.
Rain Gardens