Retrofit your yard: Build gardens that treat storm water runoff

Posted: Friday, July 11, 2003

EDITOR'S NOTE Dean Fosdick retired in May 2001 after 23 years with The Associated Press, 15 of those as Alaska bureau chief. He has covered the Exxon Valdez oil spill, volcanoes, galloping glaciers and harvesting Alaska-grown 100-pound-plus cabbages. He can be reached at: deanfosdick(at)

NEW MARKET, Va. (AP) Larry Crawford would like to flush terms like ''gully washer'' and ''mudslide'' from our collective memories, replacing them with ''bio-retention'' or ''rain garden.''

Crawford, associate director for programs and planning with Prince George's County (Md.) Department of Environmental Resources, generally is credited with designing and helping popularize rain gardens. He also helped nudge them from industrial and commercial applications to residential landscape use, where they're gaining favor nationwide.

''My background is biology and chemistry,'' Crawford says. ''I've done a lot of work in the wastewater field. We used soil there to clean wastewater, so I thought I'd like to transfer the idea to the storm-water business.''

First, though, he had to lay some groundwork. That included doing more research, developing new standards and specifications. He also helped design a manual and then began working toward moving rain gardens from factory sites to home sites all about a decade ago.

''Bio-remediation sounded kind of stiff, so we came up with rain garden, because that's what they do. They're little gardens that treat rain.''

Storm-water run-off is the nation's No. 1 source of water pollution, according to the federal Environmental Protection Agency.

Pinpointing polluters is all but impossible because contaminated runoff is caused by many activities occurring on many different kinds of landscapes. Agriculture, grazing, mining, forestry, construction, urban litter, deposits from air pollution and poorly maintained septic systems collectively contribute to polluted runoff.

''Individual actions such as pouring used motor oil down a storm drain or applying chemicals to a suburban lawn cause a further degradation of water quality,'' the EPA says.

That causes algal blooms choking waterways, fish kills, shellfish restrictions, beach closings and an increasing number of waterborne diseases.

One of the best ways to intercept runoff is by building rain gardens near downspouts, curbs, sidewalks, driveways and parking lots. Those surfaces often are the fastest routes for impure water to flow into otherwise clear ponds and streams.

Designers recommend building one or more rain gardens if you frequently see standing water or erosion in your yard, if you're concerned about the amount and quality of water flowing from your property and if you want to attract more wildlife.

''It used to be that landscaping was just a number of planting projects mounded up,'' Crawford says. ''They were disconnected from rain water.''

No more.

''Landscape architects understand that all we're doing is adding a cleansing function, making it work for us to control the natural process that goes on in the soil to clean water.''

Most of the clean-up work is done by the kinds of sediments you have underlying the gardens, the mulch you layer around the top and the root systems of the plants you choose.

Biochemical activity helps the toxins that wash down in the so-called ''first flush'' from a steady rain. The pollutants transform themselves into harmless compounds like phosphorous and nitrogen. The roots take up the nutrients.

Start by testing the soil. That will determine whether it has to be amended to speed the soak rate. Landscapers recommend a blend of 20 percent organic matter, 50 percent sand and 30 percent topsoil. Some clay around 10 percent of the total helps absorb heavy metals, hydrocarbons and other pollutants.

Let water stand too long and your rain garden will serve as just another mosquito breeding pond. Twenty-four hours to two days is a good objective, and you can tinker with the infiltration rate while you build.

Size varies but shape often resembles the saucer your grandfather used for cooling and sipping his coffee. Sink them into low points around your property areas where water naturally flows or collects.

Rain gardens mimic nature. They capture and improve water quality in much the same way wetlands and forests trap and recharge the peak flows produced by snowmelt or heavy rains.

Once you're satisfied with drainage, choose your plants. You'll need varieties effective for filtering runoff from three different planting zones.

The bottom layer should be aquatic; something that can tolerate several days of standing water. Middle layer plants should be able to take a good dunking. Perimeter or upper level plants should be capable of thriving rain or shine.

Rain gardens can be multifunctional, attractive to birds and butterflies while at the same time effective for containing and cleansing runoff.

What kind of plants do you use? Native plants primarily; varieties similar to those you see in forests, fields and wetlands around you. They're more disease resistant and require less maintenance than the exotics.

''Rain gardens are not only hydrologically functional but they're enjoyable to look at,'' Coffman says. ''Nature sells. People will pay more for the added landscaping (in real estate transactions).''

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