Rain gardens soak up excess moisture

The launch of the new year was once again wet and dramatic with all the rain and snow. I noticed that my decomposed granite driveway flooded, but my lawn and tree areas did not. These areas acted like a sponge, soaking up excess moisture. What we do in our landscapes can influence storm impacts.

Just recently, I was reading about rain gardens. A rain garden starts with a shallow depression in the ground. It is filled with permeable soil and landscaped with hardy grasses, perennials, shrubs, or trees. Mulch tops off the area. Water from storm-water runoff areas, such as roofs and driveways, is then directed to the rain garden area where it percolates into the ground instead of draining into sewers or waterways.

These rain gardens are also called bioretention facilities. Studies have shown that they actually improve water quality by trapping pollutants in the mulch and plantings. Soil organisms convert many of these pollutants into less harmful compounds.

The storm-water runoff from a roof, parking lot, or other impervious or impenetrable surfaces may not seem like a major threat to water quality. Usually we think pollution comes from a factory or sewage treatment plant and is dumped directly into a river. However, storm-water runoff carries the signature of the urbanized areas through which it flows. It contains nitrogen and phosphorus compounds from atmospheric deposition and fertilizers, as well as metals, oils, and other particulate matter. The volume and velocity of runoff from a heavy rain can overwhelm urban sewer systems. According to the U.S. Environmental Protection Agency, on a typical city block (one with 75 percent or more impervious cover), more than half of the rainwater will leave as runoff - from Michael Dietz, Ph.D., University of Connecticut, http://pubs.acs.org/subscribe/journals/esthag-w/2005/dec/tech/lt_raingarden.html

Commercial areas and large developments are usually required to create bioretention areas to reduce their polluted runoff. It's nice to know that we can do our part to improve water quality by creating rain gardens at home. Besides reducing pollution, rain gardens are attractive and may save our landscapes and grounds from damage caused by excessive runoff in times of heavy rains. Try combining a rain garden with boulders, swales, and landscaped berms throughout your yard in anticipation of nature's downpours.

For more gardening information, contact me, 887-2252 or skellyj@unce.unr.edu, or your local University of Nevada Cooperative Extension office. Check out many useful horticulture publications at www.unce.unr.edu. "Ask a Master Gardener" by e-mailing mastergardeners@unce.unr.edu.

n JoAnne Skelly is the Carson City / Storey County Extension Educator for University of Nevada Cooperative Extension.


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