written by Melissa Dalton | illustration by Edwin Ouellette
A rain garden is designed to, just as the name suggests, soak up the rainwater runoff from a roof, driveway or patio. It’s typically created by digging a shallow depression and then filling it with dirt and native shrubs, perennials and grasses. All of this works to collect rainwater and filter out the pollutants—things like fertilizer, oil and chemicals—before that water enters storm drains and ends up in our waterways. The rain garden process also replenishes groundwater and acts as habitat for local species.
Here are our tips for building your own rain garden at home:
» Note: Sometimes, the water company will offer a discount on your utility bill if you install a rain garden on your property. Check with yours! Also, always research local rules and code before starting a project like this.
① ASSESS THE SITE
First, check with local officials to make sure any potential rain garden area is free of underground utilities. Then observe where the water flows on the property to choose a spot that will best intercept it, such as at downspouts or on the edge of a paved area. Make sure the water is always flowing away from the house, and avoid any place that already puddles, as that may indicate the soil doesn’t drain well. Avoid placing the garden under trees, so as to protect their root system. Choose a relatively flat area to prevent erosion and keep existing soil stable.
② DO SOME MATH
Calculate the roof’s runoff area to understand how much water will be flowing into the garden, and size it accordingly. The garden will be roughly 10 to 15 percent of the size of the impervious surface that drains into it. When drawing the parameters, makes sure the outer edge is the proper distance from the house’s foundation. (This distance may vary depending on the jurisdiction.)
③ CHOOSE A SHAPE
The shape of the garden can be anything you want! Mimicking the organic kidney shape of a body of water is popular, even though this is not a water garden and will not collect water or breed mosquitoes.
④ ONE MORE TEST
In the center of the proposed garden area, conduct a soil infiltration test to check whether it can safely absorb the water.
⑤ START DIGGING
Outline the area with a shovel, or stakes and string. Dig out the garden area to be about 6 to 12 inches deep; this can be deeper in soil with more clay in it. Keep the bottom of the garden flat, with gently sloping sides.
⑥ ADD DIRT AND PLANTS
Depending on what’s needed, add soil, sand or compost at the bottom of the depression. Plant an assortment of natives that will be happy in that sun exposure. Then add a layer of mulch. Weed when needed. Most of all, enjoy your new garden!
