These small depressions planted with perennials, wildflowers, grasses and small shrubs look much like any other garden. The difference lies in how they’re irrigated: Rain gardens are designed to capture and hold rainwater runoff from roofs, driveways, patios and lawns.
In many places, water can overwhelm storm drains and wastewater systems during extreme rains, instead of soaking into the soil. That can cause floods in communities that have more impervious surfaces (think parking lots, sidewalks and driveways) than open space, says Yiwei Huang, an assistant professor of landscape architecture at Purdue University.
“A rain garden works like a catch pond and even small ones, if there are enough of them, can help with flood mitigation,” Huang says. “These types of gardens are a way for all of us to critically think about how we treat water and make use of it versus making it the enemy. They can solve an urban problem in a sustainable way.”
Even in places that don’t typically flood, rainwater often carries pollutants from roofs, streets and the like, dumping them in rivers and streams. The plants and soil in a rain garden can serve as a filter, helping to improve the water quality.
And of course, at a time when water is a precious commodity, an established rain garden can be self-sustaining, decreasing water use. “Think of it as greater-good gardening,” says Jeffrey Longhenry, a landscape architect in New York City.
Here’s what a rain garden is not: It is not designed to retain standing water and become a breeding ground for mosquitoes. It is not a lily pond. It is not a water feature. Water is retained for a day or two at most, then absorbed into the ground.
Building a rain garden of your own is fairly simple and inexpensive. The only costs are any new plants you need and the initial sweat equity of creating the plant bed. Here are some tips on how to get started.
Find a location in your yard where water naturally pools, says Kiers. You want to be about 10 feet — and downstream — from your home to avoid water damage to your foundation. If you have a septic tank, try to place the rain garden at least 50 feet away. Ideally, you have a downspout pointed in that direction to channel water there, but it could just be a low point in your yard. That’s your starting point. Even if your yard seems perfectly flat, that’s not the case. “Water has to go somewhere. Every home has a bit of grade so water can fall away from it,” said Longhenry.
Several variables factor into the size of a rain garden — roof size, rainfall, downspouts, yard slope and soil makeup (sandy soil drains faster than clay). The Rain Garden Alliance has a calculator on its website where you can plug in each factor and generate the approximate square footage for your ideal garden.
The next step is to dig out the lawn, creating a shallow bowl. Gradually slope the sides to about six to eight inches deep in the middle. Kiers says to think of it as creating more of a saucer than a teacup. Once you’ve dug it out, remove weeds, add mulch and start planting.
Choosing what to plant is all about balance. “You can’t use just any plant in a rain garden, but what you can use can be beautiful — an explosion of colors, wildflowers, grasses, small shrubs and wetland plants,” Longhenry said.
Look for a mix that includes varieties adaptable to both dry and occasionally wet conditions. Plants at the garden’s bottom or “wet zone” must be able to survive in standing water for a day or two, but also in low water conditions during drier times, Huang says. The middle zone, along the slope, will receive water but drains quickly, so choose accordingly. And the transition zone at the top is adjacent to a non-garden area and typically is the best spot for native perennials as it receives water during heavy rains and drains the fastest.
To find the plants that will work best in your area, search online for “plants for rain gardens in [location].” Most local nurseries and garden centers can suggest plants and answer questions, Longhenry says. You may also want to check with your local university or county extension office for rain garden plant lists.
Typically, your roof’s downspouts can be directed away from your home and toward a rain garden. Some gardeners also create rock-lined shallow ditches or swales from the downspout or other runoff spots to the rain garden, allowing water pressure and gravity to move the runoff. Or you can install a flexible underground pipe to carry the water from a downspout to the garden.
Initially, you may need to use a hose or drip system to nourish the plants while you wait for them to develop healthy root systems. But timing also helps. Kiers suggests planting in the spring along the East Coast to take advantage of summer rains. On the West Coast, a fall planting will allow you to benefit from winter rains. Once the plants take root, they should receive enough natural precipitation to thrive.
