The rain is coming — it's only a matter of when.

The rain is coming — it's only a matter of when.

And when water falls too hard or for too long, it doesn't get absorbed into the soil; it runs off into storm drains or streams, and eventually into rivers and bays. This contributes to pollution by carrying fertilizer, pesticides and roadway contaminants straight to waterways.

It's possible, though, to harness and clean this water.

"Ideally, most if not all of the water that falls on a site should stay on the site," said Zora Lathan, executive director of the Chesapeake Ecology Center in Annapolis, Md. But "we've leveled out the land and paved over paradise."

One solution to cleaning up the waterways, Lathan said, is to put contours back into the land by creating rain gardens. These are gardens that imitate nature and allow rain to infiltrate the soil, be filtered of pollutants and recharge the ground water. "We all contribute to storm-water runoff, and we need to be part of the solution."

The rain garden concept has caught on, and there are initiatives in numerous places to promote them. In Kansas City, Mo., a public-private effort launched in 2005 aims to create 10,000 rain gardens in the metropolitan area. In Atlanta, the Clean Water Campaign seeks to encourage the creation of rain gardens with a detailed how-to brochure.

Lathan said she always points out that rain gardens are simple to install. Some people have become intimidated by information about "bio-retention systems," which are often larger installations than required by home-owners. While rain gardens are a form of bio-retention, they needn't be complex or multi-layered, requiring massive earth moving or heavy labor. They can be fairly ordinary gardens of native plants.

These plants are installed in a shallow depression. "A garden in a saucer" says Lathan.

Homeowners who want to install a rain garden should do some homework first. There are issues of siting and size, and some locales are simply not right for rain gardens. It's important, for instance, that the soil underneath be permeable.

Testing the soil

The first thing a homeowner planning a rain garden should do is check the soil. Schwartz offered two simple tests:

Dig a hole six inches deep, and fill it with water. If it takes more than 24 hours for the water to drain, that's a bad spot for a rain garden. You may have compacted fill or heavy clay. If you have a place in the yard where water typically pools after a storm, that's also not a good place for a rain garden because the soil is less permeable. To check for soil type, take some dirt in your hand, add a couple of drops of water, and work it between your forefinger and thumb into a ribbon until it breaks. If it feels smooth and the ribbon is an inch or longer before it breaks, that indicates high clay content. It's not desirable soil for a rain garden.

If the soil is permeable, the next step is to figure out how big a rain garden you need. You can put in a rain garden of any size, but be aware that a very small one will catch and filter only a small proportion of the water that falls on it. Rather than planting one huge rain garden, it's probably better to plant two or more smaller ones in different areas.

Rain garden tips

Here are some tips to make the best of your rain-garden installation:

If you have poor drainage or high clay content, soil might have to be removed to a depth of 24 to 30 inches and replaced with sand. Rain gardens should be installed at least four feet above your water table. They should be at least 100 feet from a well. The slope into a rain garden should be no steeper than a 20-percent grade. Keep rain gardens two feet from property lines. Make sure that overflow will discharge in a safe direction, into planting beds, away from structures or standing water.