How to Build a Rain Garden

Too much rain can undermine a home, but a rain garden will easily solve the problem. The rain garden is planted with special deep rooted species of plants that help the water rapidly seep into the soil. The rainwater flows from the downspout and is directed away from the house and out of the lawn via a swale/stone channel. The garden bed captures the water and drains into the soil quickly.

An added advantage is mosquitoes won’t have time to breed, because the water drains within a day. This also reduces the load on the sewer system, and the amount of lawn chemicals and pet wastes that would otherwise have drained into the sewer system making its way to rivers and lakes.

Design and Build a Rain Garden

In order for water to flow into the rain garden, there must be a minimum slope of 1 inch in 4-1/2 ft. (2 percent). If the slope doesn’t exist, major landscaping will have to be done to create the slope and improve drainage.

The first step is to find a location for the plant pond. The rainwater must flow into it from downspouts, driveways or low points in the yard. Next, lay river rock for the swale. The rock should be at least 1-1/2 inches in diameter. Larger rocks may be used if desired.

PVC pipe may also be used. If the garden is more than 30 ft. from a downspout, PVC is the best choice.

Place the rain garden at least 10 ft. away from the house so water doesn’t saturate the soil close to the foundation or back up against it. If water is already pooling close to the house, channel it with underground PVC pipe.

Create an overflow for the garden. This is an area on one side slightly lower than the garden that will channel the water away when the garden fills. Be sure to locate it away from the house and the neighbors’ house as well.

Be careful not to locate the garden over the septic tank or underground utility lines.

Depth of Garden

The garden should capture only enough water to drain through the soil in 24 hours after a storm. Sandy soil will drain very quickly. Clay soil drains much slower. To test the porosity of the soil, dig a hole in the garden area about the size of a large coffee can and fill it with water. Ideally, the water should drop 1/2 inch in one hour which means or an inch in two hours. At that rate, the soil will handle12 inches of water in a 24-hour period. This makes the ideal depth of the garden 12 inches.

Plants for the Rain Garden

The best plants for the rain garden are indigenous, because they will thrive in that zone. Native grasses, wildflowers and shrubs have deep root systems. Plus they cast off their roots annually and grow new roots thereby providing more aeration and pathways for water to flow. With that said, plants for this type of garden are fairly standard:

• Aster
• Daylily
• Iris
• Sedum
• Coneflower
• Artemisia
• Sedge

The last thing a homeowner wants is a problem with a wet foundation or basement. The rain garden offers a solution. The first year the rain garden is built it’s important to mulch with shredded hardwood mulch. Other mulches will float away. Don’t forget to weed regularly. Also, during the first year, dig a notch into the berm on the low side of the garden to let about half of the water flow out. Young plants can’t tolerate a large volume of water. Add large decorative rocks at the garden’s entrance to keep heavy rain from washing out young plants. Water about an inch per week during dry spells. After that, sit back and enjoy the garden without giving a wet foundation a second thought.

Resources

Ultimate Lawn Guide, Editor and Chief Ken Collier