How to Build a Rain Garden: Capture Runoff, Protect Waterways, and Create a Beautiful Habitat

There's a new garden in town: easy to install, looks good year-round, and positively impacts the environment. It's a rain garden.

A rain garden is a shallow depression designed to collect stormwater runoff from roofs, driveways, or other impervious surfaces. Instead of rushing into storm sewers or waterways, rainwater collects in the depression, planted with native grasses and wildflowers selected for their ability to gradually absorb and filter stormwater.

Rain gardens significantly improve community water quality. Studies show up to 70% of stream, river, and lake pollution is carried by stormwater. By managing rainwater on your own property, you protect rivers, streams, and lakes from pollution. Bonus: a rain garden provides food and shelter for wildlife, and gives you a hardy, low-maintenance, naturally beautiful garden!

Siting the Garden

Locate at least 10 ft from the house. Ideal spot: a natural low area that collects water after heavy rain. Full sun preferred, but minimum half-day sun. Need a natural slope (at least 1% grade) from water collection area (roof/driveway) to rain garden. A relatively level spot minimizes digging.

Remove sod, dig a shallow depression ~6″ deep. Slope sides gradually from outer edge to deepest area. Use excavated soil to build a slightly raised berm on the lowest side to contain stormwater and allow slow percolation.

At ~6″ deep, stormwater usually absorbs within 1–7 days. Mosquitoes need 7–10 days to lay and hatch eggs, so this avoids mosquito issues. For standing water habitat (fish, amphibians), make one part deeper (up to 18″). Depending on soil (sand, clay, loam), line that area with plastic to retain a small pool.

Typical residential rain garden: 100–300 sq ft, but any size works. Most size to available space. Calculate ideal size based on roof area, soil type, and distance from house. (See links at article end for details.)

Direct downspout or sump pump outlet toward the depression via natural slope, shallow swale, or buried 4″ plastic drain tile.

Time to plant! Native plants are best—they withstand tough conditions and need little care. Consider height, bloom time, color. Plant in clumps of 3–7 of the same variety for better look than patchwork singles. Mix native ornamental grasses and sedges with perennial wildflowers for strong root mass that resists erosion and inhibits weeds.

Water new plants every other day for first 2 weeks. Once established, garden thrives without additional watering. No fertilizers needed; minimal weeding after first summer.

Most rain gardeners cut back prior year's growth in early spring. Leaving seed heads and spent foliage through winter provides visual interest, cover, and food for wildlife. Spring burning is best to knock back weeds and stimulate growth. If burning isn't an option, mow or cut back with scythe/pruners.

Applied Ecological Services, Inc. has installed rain gardens for 20+ years. Their website has excellent rain garden info, and their Taylor Creek Restoration Nursery offers a wide variety of garden plants.