Rain Garden Design 101

What Is the Purpose of a Rain Garden?

Cost effective, eco-friendly, and aesthetically pleasing, rain gardens reduce runoff that would otherwise saturate your property, help eliminate contaminants from seeping into surrounding areas and also serve as healthy dwellings for butterflies and birds. Rain gardens allow water to pool during a downpour, then slowly percolate into the soil. The shallow catch basin is a flower-bed destination for water rather than a travel route, like a swale. A fast-draining soil mix encourages water to sink in and promotes lush plant growth. Runoff may flow into a rain garden from a swale or pipe, or may simply run in from a sloping yard. Rain gardens are appropriate drainage spots for steeper slopes than swales can handle, but where the surface drops more than 3 feet over a 15-foot horizontal distance, you should get professional design help. Although a low spot in the yard might seem an ideal placement, if it stays soggy, it’s already saturated. Instead, pick an area that dries out quickly.

Calculations and Design

Designing a rain garden to handle all the runoff from a roof or driveway entails careful calculations. But you can also learn by experimenting: Build one, watch what happens after a storm, and then enlarge it as needed. Locate a rain garden at least 10 feet from your house and at least four times that far from a septic system or steep slope.

How Do You Build a Rain Garden?

Though you can excavate a small (say, 5-by-10-foot) rain garden yourself, a landscaper with an earth-moving machine will get it done faster. Make sure machinery stays along the edge of the bed so it doesn’t compact the soil as it digs a wide ­depression about 2 feet deep with gently sloping sides. Mix in compost and sand, as needed, using the same proportions as for a swale. The result should be a shallow basin with about 6 inches of “ponding depth,” or space for water to pool while it drains through 1 to 2 feet of amended soil.

Steps:

What Are the Best Plants for a Rain Garden?

Plant the center of the area with species that tolerate wet conditions, such as native sedges and lady fern. Around these, put plants suited to occasional standing water, like red twig dogwood. At the furthermost edges, add plants that prefer ­drier soil, such as native evergreen and deciduous shrubs.

What Materials Do You Need to Build a Rain Garden?

Mulch Berm or stones Perennial plants Pointed shovel Pickaxe Wheelbarrow Metal rake Hand claw

Anatomy of a Rain Garden

A: Water flows in from slope, paved area, or pipe

Best Ways to Deal with Storm Water How to Manage Storm Drainage with a Swale Use Pervious Paving Materials as a Draining Solution

B: Wide, shallow basin with flat, level bottom and gently sloped sides C: 12 to 24 inches of fast-draining D: 2 inches of mulch E: 6 inches of ponding depth F: Berm or stones to stem or slow down overflow G: Perennial plants