Our area receives a fair amount of rain in most years, and when it hits the ground, it has to go somewhere. The soil can absorb much of it. However, on impervious surfaces such as pavement and roofs, most of the water flows off the site where it enters water bodies, which increases flooding, water pollution and streambank erosion along creeks and rivers.
Homeowners can take several steps to reduce the runoff, and one way is the installation of rain gardens in the home landscape.
A rain garden is a low area that has been landscaped, allowing for runoff of impervious surfaces to collect in one area to infiltrate and be absorbed into the soil. They are a popular way for homeowners to reduce erosion and protect water bodies while improving the aesthetics of the landscape. Additionally, they can provide food and protection for wildlife.
How does one go about creating a rain garden? Construct it in a low spot near a downspout but at least 10 feet away from the foundation. Use a rope or garden hose to lay out the boundary of the garden in a curved shape. It should not be a square or rectangular, and the longer length needs to be perpendicular to the slope, while the shorter side should face downward.
The rain garden should be located where the berm, which is a small earthen dam not more than a foot high, is on the side facing downhill and is adequate to hold back the necessary amount of water. The top of it should not be higher than the uphill edge of the garden. Make sure the center of the garden is as low as possible. You may have to remove some soil to ensure the garden has the proper depth to hold up to 6 inches of water. To direct the runoff from the downspout or paved surface to the garden, build a swale, or use a corrugated drain pipe, which can be buried or above ground.
The soil should be sandy, organic and loose to allow for maximum water penetration. A general rule of thumb is that the soil should have the ability for the water to soak in at a rate of 1 inch per hour, and the garden should be completely drained within 48 hours. To determine the soil’s ability to absorb water, dig a hole 6 inches wide by 6 inches deep and fill it with water.
If it drains within 12 hours, the soil is adequate for the construction of the garden. If it takes longer, modifications are necessary for the rain garden to function correctly. To improve the infiltration ability of the soil, mix a 2- to 4-inch layer of organic matter into the soil to help improve its ability to absorb the water.
A wide variety of plants can be used in rain gardens, but they need to be tolerant of both wet and dry conditions. On the border along the upper edge of the garden and the berm, establish grass or a groundcover such as a liriope, Asia or Confederate jasmine, ajuga or mondo grass to reduce the velocity of the water entering it. Useful shrubs include Virginia sweetspire, clethra, yaupon hollies, inkberries, Florida anise, spice bush, beautyberries and buttonbush. Herbaceous perennials that thrive in rain gardens include Siberian irises, canna lilies, swamp sunflowers, goldenrod, foamflowers, Joe-pye weed, ironweed and swamp mallows. Cinnamon and royal ferns do well. Avoid plants that are susceptible to root rots, such as coniferous plants, camellias and Indian hawthorns.
Once the plants have been installed, cover the soil with a 3-inch layer of a shredded hardwood mulch, such as pine bark or cypress mulch. Remove weeds and spent flowers, and prune regularly.
Rain gardens are practical and attractive. They promote the infiltration of stormwater into the soil, decrease runoff from impervious sites and filter pollutants before they reach water bodies. Consider installing one in your landscape.
If you are interested in learning more, UGA Extension Gwinnett will hold a class on rain gardens from 6:30 to 7:30 p.m. June 19 at the One Stop Centerville center, located at 3025 Bethany Church Road, Snellville. To register, go to https://tinyurl.com/y2axsk2b, class code EXT34503.