In the Garden:
New England
November, 2005
Regional Report

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A downspout directs water from the roof into a rain garden of native perennials and wildflowers. (Photo courtesy of Prairie Nursery, www.prairienursery.com)

A Rainy Day Garden

While this fall's hurricanes spared our region the extreme devastation of the southern coasts, the endless rains did plenty of damage. Even in areas that escaped severe flooding, the rain took a toll. It dumped debris, excess fertilizer, and other pollutants from streets, yards, and farms into our waterways. It may have flooded your basement, or eroded your driveway (like mine), or created a small pond in your yard. All that excess storm water has to go somewhere.

It turns out that gardeners have an important role to play here. We can reduce the damage from runoff and enhance our landscapes at the same time by building rain gardens.

A rain garden is a mini wetland -- a place that naturally collects water flowing from the roof or driveway, street or yard, so it can gradually percolate through the soil. You can make a rain garden as beautiful as it is functional, choosing your favorite palette of native wildflowers and grasses and perennials that tolerate wet feet.

Like many homeowners, I put up gutters to solve the problem of the deluge of water that comes off my roof from rain and snowmelt. But if your downspout directs water onto a surface it can't penetrate -- like a street or driveway -- it can add to the excessive amount of water that rushes into sewers and waterways during a storm, or causes erosion somewhere on its way downhill. Lawns aren't an ideal place to empty a downspout because grass roots are shallow and can't absorb as much water as a diverse planting of shrubs and perennials in a rain garden.

Siting a Rain Garden
If you have a low spot in your yard, you already have a site for a rain garden. Otherwise you can dig one where it will provide the most benefit. Locate the rain garden at least 10 feet from your house or other buildings to keep the water away from the foundations. But, if possible, locate it close enough for it to handle water from your downspout. You can dig a shallow depression from the downspout to the rain garden or direct the water through buried drainage pipe.

Rain gardens only need to be about 6 inches deep, and the bottom should be sloped gently toward the middle. Create a berm on the downhill side to help keep the storm water contained in the garden so it can slowly percolate through the soil.

A rain garden obviously needs to drain fairly well, so if your soil is predominantly clay, you'll need to loosen it with compost, or at least dig holes through any hard layers so water can escape. As long as the water drains away within a day or so, you won't invite mosquitoes, which need several days to lay eggs and hatch.

Sizing Up the Rain Garden
If you're the type of person who likes precise measurements, there are guidelines you can follow for estimating the ideal size of a rain garden for your particular situation. For example, you'd want to measure the area of your roof that will be draining into the gutter leading to the rain garden, as well as the size of any paved areas that will be contributing to runoff into the garden. If your soil is sandy (which drains quickly), you'd want your rain garden to be about 20 to 30 percent of the area that will be draining into it (roof plus driveway, etc.) If you have clay soil, your ideal rain garden would be 60 percent of the drainage area. But don't let these numbers intimidate you -- any size rain garden is better than none at all.

Planting
The plants in a rain garden need to be tolerant of sitting in water now and then, so native plants and wildflowers are good choices because they're so adaptable. You probably already grow many of them -- ferns, ornamental grasses, sedges, iris, milkweed, asters, and black-eyed Susans, to name a few. The idea is to create a naturalistic planting that's easy to maintain (no fertilizer needed) and welcoming to butterflies and bees and other creatures.

I began collecting ornamental grasses this fall (at bargain prices) for planting in the rain garden I'm creating next spring by redirecting my downspout. It used to send water into my driveway, but after having the driveway regraded and drainage work done, I'm looking forward to solving my runoff problem and enjoying a new mini wildlife habitat at the same time.


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