Rain Garden 101

Photos courtesy Mom’s Design Build

As more homeowners look for ways to increase sustainability in their yards, while introducing more flowers and shrubs to feed the birds and the bees, rain gardens are increasing in popularity. In some cities, residential rain gardens are mandatory as part of stormwater infrastructure. Some cities also provide incentives for homeowners to get on board, with varying requirements.

So what, exactly, is a rain garden? University of Minnesota Extension describes rain gardens as “planted low areas that allow rainwater runoff from hard surfaces (like roofs, driveways, walkways, and parking lots) to soak in.” Rain gardens also “collect stormwater runoff and prevent it from flowing directly into lakes, rivers, and wetlands.”

That’s important, adds Jim Sweeney, founder and senior designer of Mom’s Design Build, because we need to be responsible for helping nature clean the stormwater in our streets, and runoff from our roofs and yards, in order to replenish the watershed without adding phosphates and other chemicals. He goes on to explain, “As the water soaks in, the soil and plants in rain gardens filter out pollutants and keep them from entering the groundwater.”

If you’re interested in the concept, says Sweeney, start by studying the topography of your yard and the grade around your house. “You’ll want to capture water coming from the roof, the gutters, and higher areas of the yard and slow it down to give it a chance to collect in the rain garden,” he says. “Look for a depression or grade change in an area that would allow water to naturally fill up. You might also run downspouts into the area or enhance the water’s run down the slope with drain tile.”

Make sure, says U of M Extension, that your future rain garden is located 10 feet or more away from foundations and basements; 35 feet or more away from the septic system; and 50 feet or more away from drinking water wells and power lines. Next, text the soil’s ability to absorb and retain water: “The soil needs to be porous enough to soak up water within 48 hours to prevent plants from drowning and mosquitoes from breeding. This is also the shortest standard period between two rainstorms.” (More information on testing your soil and sending it to a lab can be found here.)

Once you’ve determined location, soil type, and size, think about plants. “The idea is that the plants can survive both wet and dry conditions,” Sweeney says, because during extended dry periods your rain garden may go dry. “Put in native plants, as they will be able to protect your site from soil erosion, survive in wet and dry conditions, and filter chemicals out of the water.”

For moist to dry soils in a shaded rain garden, Sweeney suggests wild ginger, columbine, Pennsylvania sedge, bloodroot, tall meadow rue, wild geranium and harebell. For moist to dry gardens in the sun, choose colorful (and bee- and bird-attracting) native coneflower, butterfly milkweed, blazing star, and flat-topped aster, supplemental with such native grasses as big and little bluestem.

“We did a neat project on Lake Minnetonka, with a home in a floodplain,” Sweeney says. “We worked with city requirements and water-quality experts to design and plant a rain garden that would take on water from Lake Minnetonka, and do the work of cleaning the water before returning it back to the lake.”

In conclusion, Sweeney says, start with the correct placement of the rain garden. “Find a way to design it well within the context of your yard. If you put in an awkward spot, the rain garden will just create issues over time. If designed gracefully and smartly, however, it can do a lot of good work and be a thing of beauty.”

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