Regional Gardening Reports :: National Gardening Association

In the Garden:
New England
August, 2012
Regional Report

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Low growing Hummingbird summersweet is covered with spires of white flowers that attract butterflies from midsummer on.

Planting a Rain Garden

While our region may not be suffering from the deep drought that is affecting so much of the rest of the country, Vermont, Massachusetts, Rhode Island, Connecticut, and southern New Hampshire are experiencing abnormally dry conditions or even moderate drought. And when rain has arrived, it's tended to come down in thunderstorms that drop lots of water in a short amount of time, rather than in long, soaking rains.

Which brings me to the topic of rain gardens. These are gardens shaped like shallow bowls that are designed to capture rain water (and snow melt at other times of the year) and hold it until the ground absorbs it. When a thunderstorm unleashes a torrent of rain, all that water landing on impervious surfaces, like roofs, driveways, and walkways, often runs off into the nearest storm drain and from there eventually to local waterways, or it goes directly into nearby streams, rivers, and lakes. Even when the rain lands on lawns, gardens, or other vegetated surfaces, so much comes down so quickly in a thunderstorm that much of the needed water runs off rather than soaking into the ground.

The problem with runoff is that it can pick up and carry all sorts of pollutants as it makes its way into the watershed, from nutrients like nitrogen and phosphorous that fuel algal blooms to pesticides, herbicides, oil, grease, heavy metals, and harmful bacteria. Equally important, water that runs off is water that is not available in the soil for thirsty plants to take up.

By capturing a sudden deluge of water before it becomes runoff and letting it soak into the ground, a properly sited rain garden helps protect the environment and recharge the groundwater. And it can be an attractive addition to your landscape as well. Many of the plants that are suited to a rain garden are natives that attract beneficial and pollinating insects, butterflies, and birds. It's win win for all!

In deciding where to put a rain garden in your landscape, it's important to remember what a rain garden is not. It's not a bog or a swamp, it's a temporary water holding basin. So it doesn't belong in a spot that is naturally wet or where water stands for long periods. A low spot that is fairly flat with soil that allows any standing water to drain within a day after a storm is best. Locate it where downspouts or swales can direct water from roofs, driveways, and other impervious surfaces, but place it at least 10 feet away from the foundation of your house and away from septic tanks, leach fields, and water wells.

Similarly, the plants that are appropriate for a rain garden are not wetland plants that need constantly wet soil. Instead, choose plants that can tolerate both temporarily saturated soil and drier soil. (And because a rain garden is filled with water for only brief periods, you don't have to worry about it becoming a "mosquito garden.") Fortunately, there are a number of good online publications with information on designing, installing, and maintaining a rain garden in our region, including lists of suitable plants for a variety of settings. (See the Resource section of this report for links to these sources.)

Recently, I helped design and oversee the installation of a rain garden in Vermont Garden Park, where National Gardening's headquarters are located. A team of ambitious volunteers from Green Mountain Coffee Roasters stripped sod, excavated soil, planted plants, and spread mulch in a spot that will collect water from a wide area of the park, intercepting it after a storm before it can run off down the road. I selected both woody and herbaceous plants that provide a changing display of seasonal interest. Most are natives (or cultivars of natives) of areas of the eastern U.S. and all will weather periods of saturated soil.

Goatsbeard (Aruncus dioicus 'Kneiffii') begins the floral show in June with arching sprays of ivory-white flowers. Later, spires of fragrant white flowers adorn dwarf summersweet (Clethra alnifolia 'Hummingbird') from midsummer on, attracting butterflies and bees, while purple coneflower (Echinacea purpurea 'Magnus' and E.p. 'Green Eyes') and turtlehead (Chelone lyonii 'Hot Lips') add bright notes of color in mid to late summer. Variegated dogwood (Cornus alba 'Elegantissima') provides year-round interest with its green and white variegated leaves in summer, red stems in winter, and white berries that attract birds. Inkberry (Ilex glabra 'Shamrock') with its narrow, glossy evergreen leaves provides a nice textural contrast to the lady ferns (Athyrium felix-femina) that fill in the shadier side of the garden.

This new garden is now a lovely spot that will help the environment, wildlife, and the water table. And other people did all the work of putting it in. How great is that?

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