Rain gardens, designed to slow and trap storm water, are good for the garden and the environment.
A downspout descends from the side of the brick Colonial house of Andy and Shizumi Manale in Silver Spring, Md., but instead of emptying into the foundation bed, it stops about eight feet above the ground, where it moves over the path, like an arch, to empty into a bed of shrubs and perennials on the property line.
For the hostas and azaleas, it's bathtime.
Shizumi Manale disappears as her husband explains that he hates to waste bath water. She has gone upstairs to pull the plug on the tub (actually, to turn on a pump), and after a few seconds, water comes gushing out of the downspout, down a Japanese-style rain chain attached to it and into the growing beds. Andy Manale offers a proud grin, but the recycled bath water is just one way that he irrigates his lush garden. In virtually every garden area around the house, the land brims with rainwater from the roofs and from three sump pumps.
The Manales live in a typical Washington neighborhood of sticky clay, high water tables and water seeping into the street. But even in a year of excessive rain, "very little water actually leaves my property," he said.
They are among a pioneering class of gardeners who have turned to rain gardens, designed to slow and trap storm water in a way that's good for the garden and the environment. The plants love it, and the Manales have done their bit to prevent runoff from polluting local waterways and, ultimately, the Chesapeake Bay.
Before urbanization, the marshland and forests held rainwater, filtered it and allowed it to seep slowly into aquifers and streams. In our modern world of roofs, parking lots, roads and lawns, fast-moving water carries pollutants to the bay and, through its sheer energy, erodes and silts the ailing estuary and its tributaries.
Although the pre-settlement swamps of Washington have gone, "we can mimic what the wetlands used to do," said Andy Manale, a policy analyst and biochemist at the Environmental Protection Agency.
Rain gardens have become an increasingly popular component of eco-gardening in an age of global warming and weather extremes. Some local jurisdictions give grants to defray their cost.
But to create one, you have to dig. The water is arrested by working the earth: removing compacted clay soil and backfilling the excavated area with a permeable soil mix containing lots of gravel or sharp sand. Buried perforated pipes take the water away to distant parts of the yard. About 10 minutes after the bathtub demonstration, Shizumi Manale called from about 30 feet away to point out a plant border in the lower lawn. "I see the flowing water," she said.
The Manales have positioned large steppingstones in these water courses and planted them with perennials, shrubs and trees that can take brief periods of wet soil. Choices include azaleas, hostas, pulmonarias — plants that like moist soil but can take dry conditions once they have become established and develop deep roots. Because these gardens are free-draining, they remain saturated for hours, not days, and thus allow a fairly broad palette of plants.
The Manales began building their rain gardens soon after moving to their home 21 years ago, and the features can be found on all four sides of the house. More are planned, and existing ones will be refined. "It's about observing what's happening on the land," Andy Manale said. "Where do I have runoff, where do I want to slow it down, where do I plant trees to take advantage of the water?"
To create theirs, the Manales excavated as deeply as three feet or more, a depth that would require knowing the exact location of buried utility pipes and wires, not to mention a strong back. He used much of the surplus clay to form a berm behind a fish pond.
Ann English, a landscape architect who designs rain gardens, said gardeners in Seattle have created effective versions by excavating as little as six inches. In an online manual she has written for homeowners, she suggests beds be excavated between eight inches and three feet. The less the depth of amended soil, the wetter the site, and the greater the need to select flood-tolerant flora.
English, a member of an environmental organization in Beltsville, Md., named the Low Impact Design Center, suggests a soil mix of 50 percent coarse sand, 30 percent low clay topsoil, 15 percent shredded hardwood mulch and 5 percent peat moss. The Virginia Department of Forestry suggests 50 percent sand, 25 percent topsoil and 25 percent compost or leaf litter.
English has also designed plans of plant combinations that can be used in given situations: for example, a 450-square-foot rain garden to attract and sustain birds, a 900-square-foot hedgerow for partial shade, and a 150-square-foot corner bed in full sun. (You can find them at www.lowimpactdevelopment.org.)
An actual rain garden is at Brookside Gardens in Wheaton, Md., where English worked with others to design the public garden's large-scale demonstration rain garden near the conservatories.
Formerly a series of cascading ponds, the hillside garden was routinely washed out in storms as water sheeted down a broad pathway and poured off a sloping field. It was so bad that staff had to drain the ponds before anticipated deluges, and even then gardeners would routinely have to retrieve and replant perennials and bulbs that had washed into the parking lot.
Completed with grants and donated labor and materials from a contractor, J&G Landscape Design, the $80,000 rain garden features an upper shade garden covering 175 square feet, where water seeps and drains into the lower garden of 550 square feet in full sun. The garden is framed by paths made from permeable pavers laid on an 18-inch bed of gravel. In its first really wet spring, it has performed admirably, said Lisa Tayerle, its gardener. "In March the garden had six to eight inches of rain, and two hours afterward, two-thirds was gone," she said. "It's working really well."
One of the key features of the upper basin, said Brookside's Phil Normandy, is the creation of a lip to form a bowl to hold the water. The depression is planted with wood asters, goatsbeard, lady ferns, two species of wood ferns and wild geranium. The lower garden is a medley of native plants, including two species of amsonia, goldenrod, coneflowers, New England asters, baptisia and great blue lobelia.
Normandy said the concept of a rain garden evolved from the use of storm water management ponds commonly found wrapped in chain-link fencing in shopping malls or townhouse developments, empty, littered and weedy. "These are basically dry ponds full of water when it rains and an eyesore the other 11 1/2 months of the year. The idea was that you can make this permeable space beautiful, and this is a surprise to a lot of people."
"In my mind," English said, "the ideal rain garden is one where you don't walk by and say, 'Aha! a rain garden.' It's just a beautiful garden." Even if it's in your back yard.