Rain gardens capture, filter rainwater

May 11, 2010|By ANNETTE IPSAN

What is a rain garden? It's a garden that captures and filters rainwater. And it's all the rage among those who want to protect the environment and keep pollution out of the Chesapeake Bay and other waterways.

Rain gardens are sunken gardens planted with native plants. Placed so they collect rainwater from a downspout, these gardens slowly filter the water from your roof, preventing erosion, trapping pollution and restoring natural water flow.

Traditional stormwater management emphasizes moving water away from a home as quickly as possible. It revs off the roof, down gutters, across driveways and lawns, and into the street and storm drains. As water moves across all these hard surfaces, it collects soil, fertilizer, oil and chemicals that pollute our waterways and clog them with sediment.

Rain gardens slow and clean rainwater at ground zero: your home. They intercept the rain from your roof and filter it using plant roots. Native plant roots are especially good filters, stretching deep into the soil. Water pools for an hour to a day, then disappears. That's nature's filter at work. Some U.S. communities mandate rain gardens for natural stormwater management.


Are you ready to make your very own rain garden? First, place it where the rainwater flows, often from a downspout. It should be at least 10 feet away from your home's foundation in a level area. Avoid septic drain fields and areas that are perpetually wet since this indicates poor drainage.

Next, dig a shallow bowl 3 to 6 inches deep. Most rain gardens are oval or kidney shaped. It should be about a third of the size of the area of the roof draining into it. Any size rain garden will help filter some rainwater, but this is ideal.

If one side of the rain garden is slightly lower than the other, you can create a berm, a low mound of soil that will help hold the water while it's being absorbed.

Now you are ready to fill your rain garden with native plants. Native plants are tough broads, as resilient as they are lovely. They've been here since before the European settlers, so they have weathered cold, hot, wet and dry years. They take less water to establish and attract birds, butterflies and beneficial insects. They co-evolved with native wildlife and support a balanced ecosystem. Can you tell I'm a fan?

You already know many native plants - Black-eyed Susan, Joe Pye weed, purple coneflower - and there are hundreds more to choose from. For a rain garden, choose native plants that can handle both wet and dry conditions. Most local nurseries carry a few. Many can special order others.

A good source for information on native plants is the Maryland Native Plant Society's website, Our own Home and Garden Information Center website - - lists native plant nurseries and has a downloadable native plants booklet.

After you've chosen and planted your native plants, water them to get them established (yes, I know that seems ironic given that this is a rain garden you're creating, but all new plantings need water to get going.) Then, enjoy watching your rain garden doing its thing.

We just added a rain garden to our Master Gardener teaching gardens at the Extension offices. And I must say, I do enjoy watching the rain pool and get slurped up by the garden. It works. And it feels good knowing that we are helping to restore groundwater, prevent erosion and pollution and adding a bit of beauty with a wonderful mix of native plants. If your community group would like an educational tour of our rain garden, just contact me by e-mail or phone.

Annette Ipsan is the Extension educator for horticulture and the Master Gardener program in Washington County for the University of Maryland Extension. She can be reached weekdays by telephone at 301-791-1604, or by e-mail at">

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