A Perennial Powerhouse
1 Jan, 2008 By: Robert Scheyer LivescapesCan curbside perennial gardens improve water quality? Environmental and community groups, and even City Hall, are adopting a landscaping technique called "rain gardens" to find out.
Rain gardens are curbside perennial plantings that trap what the Environmental Protection Agency calls "non-point source" water pollution. Non-point water pollution is runoff from impermeable surfaces that collect dirt, fertilizers, chemicals, oil and bacteria. It is simply what accumulates in the normal course of property ownership among responsible people. These same property owners are organizing themselves to reduce this source of pollution by having eco-friendly rain gardens installed. It's a win-win proposition for communities and landscapers.
 PERENNIAL PLANTINGS will help filter out any runoff before it reaches the storm drain. |
An Idea is Planted
Rain Gardens were first conceived in 1990 by Larry Coffman who was heading up Maryland's environmental programs. He was investigating cost effective, low maintenance methods for improving water quality in local watersheds. With the help of his staff, they came up with the idea of "bioretention," or capturing storm runoff in plant systems.
"I began to realize that we could use the functions of the upland ecosystem to treat storm water runoff," Coffman says. "One other fact that influenced my thinking was the studies we were getting back on BMP (best management practices) efficacy. They showed there were major problems with cost, maintenance and operations. So, I got the idea of designing the green space in a parking lot to treat the runoff."
 WHEN EXCAVATING a rain garden, be sure to leave a lip of soil on the downhill side of the newly dug swale. |
In 1997, in cooperation with the University of Maryland, Coffman and his staff began testing for the most effective design.
"Since then, we have improved the design and learned about the whole new world of the complex and wonderful plant/soil/microbe ecosystem," Coffman says, "and how to use nature to protect nature and make things prettier too."
 CLOSE-UP of the lip of soil that is key to trapping runoff. |
The term "bioretention gardens" was a little clumsy, so Coffman coined the term "rain gardens."
Proper Placement
Coffman's final design emphasizes location, location, and location.
 TILL IN soil amendments before planting. |
A rain garden must catch and hold water runoff before it gets into a storm drain. So, wherever storm water runoff collects or flows is a prospective site. Likely sites include the bottom of a hill or ravine; or on a slope through which water flows.
Other important considerations are size and shape. A Rain Garden should be about 20% the size of the roof, patio, or pavement area draining into it. In most cases, this will be between 100 and 300 sq. ft. The shape should be both ascetically pleasing and appropriate to catch water runoff. Although, since site selection is the key, even a small garden, when properly placed, has an impact.
 RAIN GARDENS are often installed at the end of a yard, but can also be useful wherever there is a slope. (PHOTOS COURTESY: GARDENSCAPES) |
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