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Rain gardens filter runoff, keep pollutants out of streams

Tuesday, April 29, 2014
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Mike and Jane Banefield of Williamsburg, Va., work on a rain garden on a slope that required a build-up on the downhill side. They are digging out and leveling the basin for the rain garden within the built-up area; two extended drainage pipes from the roof are directed into the rain garden for the water inflow into the rain garden. (Carol Fryer/Newport News Daily Press)
Mike and Jane Banefield of Williamsburg, Va., work on a rain garden on a slope that required a build-up on the downhill side. They are digging out and leveling the basin for the rain garden within the built-up area; two extended drainage pipes from the roof are directed into the rain garden for the water inflow into the rain garden. (Carol Fryer/Newport News Daily Press)

Rain is a natural resource for your yard.

Think of it as pennies from heaven — free moisture that nourishes your plants and nixes high water bills.

Ask a master gardener how best to access that rich resource and you are likely to hear “rain garden.” A rain garden is also a fuss-free way to help clean up our environment.

When it rains, water falls on roofs, driveways, lawns, between houses, over parking lots and through storm drains. As stormwater travels over these surfaces, it collects pollutants, pesticides, herbicides, sediments and pet wastes. In undisturbed landscapes, such as woods and open field, there is very little stormwater runoff because rainwater filters through soil or evaporates into the atmosphere.

“Seventy percent of pollutants in our streams, rivers and lakes are carried there by stormwater,” says Carol Fyrer, a master gardener in Williamsburg, Va. She and other master gardeners are using their skills to help homeowners develop rain gardens in places where erosion, water conservation and pollution control are concerns.

“Most people do not know that about half of the pollutants are caused by what we do in our gardens and yards. Planting a rain garden might seem like a small part of stormwater management, but if you calculate the amount of rain that runs off you roof, you might be very surprised. Water running off a house roof can be channeled into a rain garden, rather than heading into the street to a storm drain carrying pollutants with it.”

Rain garden tips

-- Check your property and note where rain runs off during a rainstorm.

-- Do a soil test to determine the make-up of your soil.

-- Do an infiltration test at garden site to see how quickly water seeps into soil.

-- To determine garden size, calculate how much rain flows to the area from impervious surfaces — roof, driveway, sidewalk — and pervious surfaces, such as lawn and other plant beds. Formulas are available online, at Rainscaping (www.rainscaping.org/index.cfm/fuseaction/home.sizecalculator/index.htm) and the Rain Garden Alliance (raingardenalliance.org/right/calculator)

-- Before you dig, lay out a water hose to the dimension and shape desired of your rain garden to get a sense of what it will look like, and adjust the shape until it is pleasing to you.

-- Research native plants that might work for you, and locate nurseries where they are available.

Learn more about rain gardens through the Rain Garden Network at www.raingardennetwork.com.

A rain garden is an attractive landscape feature designed to capture, filter and infiltrate stormwater back into the soil — rather than rain running off your property or causing erosion, according to Carol.

“They are built as shallow depressions — basins — in the ground that are filled with good draining soil mix and beautiful plants that can tolerate wet soil and periods of drought,” she says.

Natural filters

As water collects in the rain garden, it is filtered and slowly absorbed by soil and plants. Soil and plant roots of the trees, shrubs and perennials planted in the rain garden filter pollutants, pesticides and herbicides from the rainwater. Well-designed rain gardens will hold water for no longer than 24-48 hours.

Rain gardens have several advantages, according to Darl Fletcher, assistant horticulture curator at the Virginia Living Museum — www.thevlm.org — in Newport News, Va. The museum’s rain garden is in front of the green roof of the Goodson Living Green House, and is planted with witch hazel, sweet pepperbush, strawberry bush, Virginia sweetspire and copper iris — all native species.

“Rain gardens help reduce and filter stormwater runoff, which reduces stormwater pollution as well as increases groundwater replenishment,“ says Fletcher. “They provide habitat for wildlife, are attractive, are low maintenance — do not require mowing, fertilization or watering once established — and can increase property values with their use of creative landscape design.“

A rain garden should be at least 10 feet from a house so water soaking into the soil does not seep into the foundation. Do not place the rain garden directly over a septic system, or underground utilities.

A wet area of your land may not be a good spot since the infiltration is poor there. An area closer to the runoff source — roof or driveway — to intercept the water is a better choice, according to Carol.

If your water table is high, less than 2 feet deep from the surface, a rain garden will not work since infiltration is an issue, she adds.

Locate a rain garden in sun or partial sun, not directly under a big tree.

Placing a rain garden in a flatter part of a yard makes digging much easier.

A slope of less than 12 percent grade work is best since the base of the rain garden must be level, and less incline requires less filling in of the downward side of a slope.

 
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