Sustainable Landscape News Distributed 05/01/09
By LSU AgCenter sustainable landscape experts Dan Gill, Rod Hendrick, Allen Owings and John Young
A rain garden is a depression in the landscape that catches runoff from rain and contains water-tolerant plants.
The depression may be a natural low spot, or it may be constructed. In either case, it holds runoff until the water can soak into the ground. Such a system also helps remove organic matter, nutrients, soil and other pollutants before the water reaches storm sewers, lakes and streams.
If you have a low area that you’d like to convert to a rain garden, the procedure is simple. Dig out the area and put a layer of gravel or coarse sand in the depression. On top of that, place a mixture of pine bark and compost. Finally, add the plants. This design allows plants that are adapted to wet areas to thrive where they otherwise might not because of saturated soil.
If you are building or redoing your landscape, you can design and slope it to provide sites for one or more rain gardens.
Rain gardens may be wet or dry. A wet rain garden stays wet or damp for an extended period of time, whereas a dry rain garden collects rainwater but dries out after a few hours. Plants are available for either type. You might want to construct both types to show off a variety of specimens in your yard. In any case, you are helping to reduce flooding and keeping nearby lakes and streams cleaner.
Flooding and pollution from runoff have been increasing as streets, driveways, houses and lawns replace natural areas. The more we develop an area, the greater the total runoff becomes.
Runoff from urban neighborhoods can contain as much as 21 pounds of nitrogen per acre per year. High levels of phosphorous, high loads of solids and very high bacteria counts also pose a problem.
Nitrogen and phosphorous are nutrients that promote algae growth in streams and lakes that can lead to fish kills. Solids like soil, leaves and grass clippings can fill in stream beds, reducing volume and increasing flooding. Bacteria that cause sickness can close waters to swimming, fishing and oyster harvesting.
Rain gardens can divert some of this water by letting it soak into the soil or delaying its entry into the ditches and storm sewers where it contributes to flooding.
Details on building rain gardens and suitable plants for both wet and dry rain gardens can be found on the LSU AgCentor’s Web site by typing rain gardens in the search box. A list of plants that thrive in wet conditions in Louisiana is also available.
Both wet and dry rain gardens can be seen in the landscape at LaHouse located near the intersection of Burbank Drive and Nicholson Drive (La. Highway 30) in Baton Rouge across the street from the new LSU baseball stadium. Go online to Louisiana Yards and Neighborhoods for additional information.
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Editor: Mark Claesgens