All You Need to Know About Rain Gardens

Capture and utilize rainfall in your garden before it disappears down the storm sewers with these intriguing landscape features.

By Glenda Taylor | Updated Mar 14, 2018 2:00 PM

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All You Need to Know About Rain Gardens

Photo: via Wisconsin Department of Natural Resources

A rain garden is an excavated depression, surrounded on one or more sides by an earthen berm for water retention, and then filled with porous soil and native plants that thrive solely on rainwater runoff. The concept behind these brilliant beauties was a desire to conserve water, add a natural element to the landscape, and reduce the runoff that infiltrates municipal drain-water systems. The rainfall that hits a typical neighborhood’s roofs, patios, and driveways is diverted into storm sewers—and wasted. But by directing runoff from your roof gutters and drain spouts, as well as paved areas, into an earth basin, you can grow a gorgeous garden that’s also an oasis for songbirds, turtles, and a host of other creatures right after a rain. Find out how here, and you’ll never begrudge a rainy day again!

Test Soil Drainage Requirements
Immediately after a rain, a rain garden resembles a natural wetland—but within a day or two, the water should recede as the ground beneath absorbs the excess. This absorption prevents long-standing water that might otherwise stagnate and lead to mosquito breeding. Rain gardens are suitable for most types of soil except heavy clay, which doesn’t offer adequate drainage. In order to test your soil’s draining potential, dig a hole 1 foot deep and 1 foot in diameter. Fill it with water and, once it drains, fill it again. If the second filling drains completely within 24 hours or less, your soil will make a fine host for a rain garden. Don’t despair if the spot proves unsuitable; soil content can vary within a yard so test other areas.

Find the Right Location
Rain gardens are naturally suited to the lower areas in your yard. So to find the perfect spot, the next time it rains, go outside and watch the way the water travels. Does most of the runoff come from your home’s downspouts? Where does it go from there? How much runs off your driveway and yard?

Logically, you’d want to locate a rain garden in a natural drainage path, but depending on the contour of your yard, this may not be possible. The answer is to then divert runoff to the rain garden, via swales (shallow grassy trenches that serve as ditches to carry runoff) or buried pipes that transport runoff from downspouts or other areas to the rain garden.

Account for Overflow
The successful rain garden will have an inlet where runoff flows into the basin and an overflow outlet for excess water to escape. The outlet, which can be a pipe or even a notch dug out of the side of the berm, will ensure that the plants are not subjected to flooding conditions.

All You Need to Know About Rain Gardens

Photo: via Carron Brown

Size It Right
Because every yard is different—some being relatively flat while others slope steeply—no two rain gardens will be the same size or shape. The contour of your rain garden is up to you but give some consideration to how the finished rain garden will fit into the landscape. Think of your yard as an artist’s canvas; a large rain garden can visually overwhelm a tiny yard, while a tiny one might seem like an afterthought in a large expanse. If you’re creative and have enough yard space, you can even install a series of rain gardens so overflowing water from one basin fills the next basin.

Pick Plants and Materials
The best plants for your rain garden are those that grow well in your area and can tolerate drought as well as occasional flooding conditions. It’s better to fill rain gardens with growing plants, rather than seeds that can wash away if a heavy rain washes out the spot before seeds have a chance to sprout and establish root systems. Think of plants found alongside rivers and seasonal creek beds in your area.

Good choices include, but are not limited to, ornamental grasses, berries, and cattails. Arrange the plants so the ones most tolerant of standing water are in the lowest areas of the rain garden. To visually enjoy the garden as a whole, it’s a good idea to put taller plants toward the back where they will not block the view of smaller plants. Feel free to place large stones, petrified logs, and other natural elements in your rain garden to give it a woodsy look.

Build It Wisely
The first step in constructing rain gardens is to call Dig Safe at (811), a free service from local utility companies. Reps will come out and mark your lawn to indicate the location of buried lines so you won’t disrupt them when you dig. Excavate the rain garden basin and the drainage system that will direct water to the basin. It’s quicker, and easier on your back, to rent a skid steer (from a construction rental store) if you’re installing a sizeable rain garden, but a regular garden shovel will also work. Depending on your design, the ditches can conceal buried pipes, or they can be simple swales, which divert runoff to your rain garden. Use excavated soil to form berms around the basin, if needed, to help retain water on the low edges, and position the inlet and the overflow outlet.

Fill the basin with amended soil. Pre-mixed soil mixtures, labeled “rain garden soil” are available in some regions, but you can also create an optimal DIY mixture by combining 50 percent sand, 25 percent compost, and 25 percent topsoil. Add the plants you selected and apply a couple of inches of good shredded hardwood mulch, which is heavier than softwood mulch and less likely to float away, to discourage weeds and help retain moisture during dry spells. For the first year, water the new plants to help them develop root systems.

Enjoy Low Maintenance!
Once established, your rain garden will be a sustainable, low-maintenance landscaping element that requires only occasional weeding or refreshing the mulch by adding of a few inches of new mulch once a year or so.