Everyone benefits when you build a rain garden

Think of a rain garden as a sponge — a pretty, environmentally friendly sponge.

Rain gardens are groupings of plants designed to soak up runoff from roofs, driveways and lawns.

Why is that important? As storm water runs over lawns, streets and other man-made surfaces, it picks up pollutants — phosphorous and nitrogen from fertilizers, bacteria from pet waste and road salt, to name a few — and carries them into local streams and lakes.

When homeowners help water to flow into a rain garden, the plants help absorb that runoff water to keep pollution from washing into local watersheds and to help prevent flash flooding.

Compared with a normal lawn, rain gardens allow about 30 percent more water to soak into the ground.

"They're just fun," said Amy Samuels, a natural resources team coordinator with Cornell University Cooperative Extension in upstate New York. "You're making this thing that can help prevent pollution. You get to choose neat plants and make your garden look beautiful."

Here's how to get started building a rain garden:

Find a location. The best sites are those with partial to full sun. Rain gardens should be at least 10 feet away from a home to prevent leaks into your basement.

Water can be directed to gardens that sit far away from a home with plastic piping. But make sure you don't build your garden over a septic system or pipes. Before you break out a shovel, have utility workers come to your home and mark the location of underground lines.

Choose your plants. Use a variety of heights, shapes and textures, and pick plants that bloom at different times during the season. Try incorporating native species. "We like to recommend native plants because they frequently have wildlife benefits," Samuels said.

Dig. A rain garden is usually 4 to 8 inches deep with the cross-section of a pie tin: the bottom should be flat, with angled sides. Residential rain gardens usually span between 100 and 300 square feet and are built in a kidney or tear-drop shape.

Use dug-up soil to create a berm, or low wall, around three sides of the garden to hold in water during storms. Add compost to increase drainage.

Plant, water and mulch. Your rain garden will need water, especially when it's first installed and during dry spells. Like any garden, rain gardens also need to be weeded, mulched and, eventually, thinned.

"A lot of these plants will take regular garden conditions, too, so you can plant them elsewhere," Samuels said. "Then one garden becomes the source of another garden."