A rain garden sits between a downspout and the street to prevent rainwater from reaching the storm sewer. Excavated, backfilled with free-draining soil and landscaped with a range of plants that can cope with periodic flooding, the rain garden holds water for a day or two until it can percolate into the soil. The plants also drink up some of the water.
The draining quality prevents a breeding ground for mosquitoes — the insects need a week of standing water to develop — and the rain garden also reduces the amount of metered tap water or precious well water used to keep a garden going.
The District and Montgomery County offer homeowners technical assistance and grants to install rain gardens, and other area jurisdictions are likely to follow suit as these gardens catch on.
“Homeowners are just embracing the concept,” said Leah Lemoine of the District Department of the Environment. “They love the idea of using rain gardens to help the environment.”
In the past two years, the department has used its RiverSmart program to help residents install 139 rain gardens, 176 related plantings called conservation landscapes and 1,112 rain barrels.
We visited three area homes whose owners have markedly reduced the amount of rainwater leaving their properties.
The front yard of Jamal Kadri’s rowhouse on Independence Avenue in Southeast is just 18 feet from sidewalk to front door, and his rain garden occupies about half of it. The downspout, which once tied into the city storm sewer, is now connected to a drainpipe that feeds the new garden. With family and friends, Kadri spent a day digging out the old clay soil until he had excavated 50 loads in a five-gallon bucket. He used most of the fill to form a berm next to the house to keep the water from seeping into his basement.
Kadri then backfilled the garden with sand and topsoil and a bit of rotted horse manure to populate the new garden with beneficial microbes. Two years later, the native plants in the bed are vigorous from the moisture, and include the shrubs arrowwood and sweetspire, switch grasses and the native pond iris called blue flag.
Kadri designed the garden to take two inches of rain, all but the worst storm. Only in an extreme deluge will water seep over the sidewalk, he said. In his back yard, he has diverted the rear downspout to a 130-gallon rain barrel that sits on a platform of recycled bricks. In a heavy rainfall, the excess overflows into soil beneath.
He said he spent about $300 for the plants in the front rain garden, and paid a contractor $200 to disconnect the old downspout in the rear and install a new pipe to feed the barrel.
He loves the front garden’s utility and beauty. “It used to be a gray funnel, and now it’s a green sponge. It’s pretty much soaking up everything that’s coming into it,” he said.
In Chevy Chase, Cathy Pickar wanted to take advantage of having a contractor on-site — she and her husband were adding to their house — to create a rain garden that now forms a major landscape feature on the right side of their lot.
The garden is not fed by downspouts but captures the storm water that gathers from the roofs and yards of neighbors uphill in the town of Somerset. Heavy storms, she said, would create “a river” through the grassy yard. The water is now largely contained by the 300-square-foot garden that ties in to existing beds. Moisture-loving plants soak up the rain, including a sweetbay magnolia, sweetspire, beautyberry, creeping sumac and winterberry, as well as ferns and Siberian irises.
The garden was designed as part of a larger landscape installation by Laura Will, of Willow Landscape Design. Pickar said she had seen other rain gardens that look dry and unattractive and wanted the bed to look as handsome as any other part of the garden.
Montgomery County’s rain gardens expert, Ann English, had suggested placing the garden on the side of the yard where the storm water enters, not where it leaves. This frees more of the land from flooding.
Pickar said the contractor used a backhoe to excavate the bed down to about six feet. This is considerably deeper than the standard 18 to 40 inches. The depth is driven by how much rainwater you want to capture, your soil type and other conditions. English said it would make no sense to dig so deep a garden in a location with a high water table — it would simply fill from below ground. Shallow beds can be used as rain gardens, but you need a greater area to do the same work, and they stay wetter longer, further reducing the range of plants that can be used.
At a minimum, she said, the gardens should capture half an inch of rain, preferably an inch, which would handle about 90 percent of the storms we get in Washington.
Eileen Straughan owns an environmental consulting firm in Columbia, so she decided she needed “to walk the walk” at her home in Colesville, an 11-year-old infill development on formerly wooded land. If the community were built today, she said, the developer would have to meet modern storm-water management requirements. But until she reworked her landscape, rainwater coursed along a swale from her neighbor’s uphill and dumped into a storm drain on the other side of her back yard.
Two years ago, she hired a contractor to install two related features. Her rain garden is a kidney-shaped bed approximately 20 feet long and eight feet wide that was excavated to three feet before backfilling and planting with grasses, milkweed, winterberry and redbud. The swale below it has been converted into a broad, meandering feature called a conservation landscape — a low bed planted with swamp plants without the amount of preparatory digging found in a rain garden. Straughan’s version, however, contains three dry wells — 10-square-foot holes dug to 30 inches and filled with decorative gravel. The bed is the entire width of the yard, about 100 feet, and 20 feet deep, and features native lowland plants arranged aesthetically. They include the shrubs clethra, sweetbay magnolia and buttonbush, and herbaceous plants such as hardy hibiscus, switch grass and northern sea oats.
Straughan also has diverted downspouts into two rain barrels, a handsome whiskey barrel on her rear deck and a recycled plastic keg on the side of the house. The white keg works fine for washing the car, though she offers this advice: “Paint it. Enough light gets through for algae to grow inside.”
To find plants suited to rain garden conditions, check out these Web sites:
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