How to Design a Rain Garden, a Beautiful Way to Manage Stormwater Runoff

Whether you live in a place that experiences a lot of rainfall or very little, having a place to channel excess water is a must. But if your landscape has impermeable structures, rain water often travels into storm drains, carrying unwanted pollutants with it. An aesthetically pleasing solution you can try? A rain garden. The system pushes rain water into a location where it can successfully drain. In this area, gardeners can plant beautiful, moisture-tolerant plants that give the space charming character. We asked experts to share tips on how to design a rain garden that fits into your landscape.

What Is a Rain Garden? 

A rain garden is a landscape feature designed to capture and absorb rain and moisture that would otherwise be lost to runoff and travel down your storm drain. “In managing runoff, this gives you control of where water accumulates,” says Justin Hancock, a horticulturist at Costa Farms. “It also helps reduce some potential pollutants.” If designed thoughtfully, rain gardens provide a habitat for wildlife and can add beauty to your landscape.

Will a Rain Garden Work for Your Landscape?

First, determine if there is a lot of water hitting impermeable surfaces of your landscape. "This includes roof space—such as over your home and garage—sidewalks, walkways, driveways, or even large patio spaces," says Hancock. "If there is a lot of water hitting these surfaces, you’ll need to ensure there’s a sensible place to send that water." Building a rain garden that’s lower than the surrounding landscape makes it easier to funnel the water there.

Before you get started, however, you'll need to make a few phone calls: Be sure to check with your local municipality and homeowners association to get approval for building a rain garden. 

Factors to Consider When Choosing a Location for a Rain Garden

As you decide where to place your rain garden, look for an area that is sized appropriately for the amount of rainfall it will capture—and be mindful of the rain garden's proximity to your foundation. "Be sure they don’t create additional drainage issues with foundations or basements," says Joe Raboine, director of residential hardscapes at Belgard. As a general rule, rain gardens should be relatively far from the home’s foundation and situated on a downward slope. 

Sunlight

A rain garden can exist in a sunny or shaded area. “You would simply adjust the plant palette you use based on lighting conditions,” says Hancock. If there’s only one area in your yard where a rain garden is suitable and the location happens to receive full sun, then you should opt for plants that can withstand at least six hours of sunlight. 

 Soil

Rain gardens can be built in any type of soil, but well-draining soil is ideal. “If your yard has a particularly high amount of clay, digging your rain garden extra-deep so you can backfill with a better-draining soil can be especially helpful,” says Hancock. 

Water

How much water your plants need when it’s not raining depends on the varieties you choose to grow. “If you want to use a lot of plants that like and need evenly moist soil, then you may want to irrigate your rain garden during dry periods to keep it looking its best,” says Hancock. “If you select plants that can tolerate a bit of drying out, then additional irrigation may not be necessary, except for in times of drought.”

Designing a Rain Garden

While there is no hard and fast rule for what a rain garden should look like, the more runoff your yard has, the larger this plot should be. "One general rule you’ll see designers talk about is that your rain garden should be about 10 to 15 percent the size of the surface area that generates the runoff,” says Hancock. “If you’re in an area that frequently experiences very heavy rains, you might want to make it a little larger (or deeper) so it can accommodate most or all of the runoff without overflowing into the rest of your landscape." If you live in a drought-prone area, opting for a smaller rain garden should be fine.

Prepare the Soil

Start by removing all existing vegetation, including grass. This can be done with a rototiller, sheet mulching, a shovel, sod cutter, or other methods. Once the vegetation is gone, you can begin digging. There are three main factors that determine how deep your garden should be. First, if you're starting on a low spot where water naturally collects, you may not need to dig so deep.

The second factor is how big or small your rain garden is. "The smaller the rain garden (compared to the amount of impermeable surface), the deeper it will need to be so it doesn’t regularly flood the rest of your yard," says Hancock.

Finally, soil type also plays a role. If you’re not sure what type of soil you have, try digging a 1 x 1 x 1 foot hole in your yard; water the surrounding area well and fill it with water. "If it takes more than an hour or so for the water level in your hole to go down 1 inch, than you may want dig at least 4 to 6 inches deep," says Hancock.

Select Your Plants

Now it's time for the fun part—choosing your plants. "Start with plants that don’t mind having wet feet and that match your site’s sun, shade, and USDA hardiness zone conditions," says Hancock. "Your rain garden may have trees, shrubs, annuals, perennials, or even vines." Many people opt for native plants, as they don't typically require supplemental irrigation beyond rainfall, but this isn't a requirement.

Add Your Plants

When you're ready, add the plants to your garden. This is best done by working in layers. "Aim to have the most water-loving plants closest to the deepest part of your rain garden—especially if you receive a lot of rain and have clay soils that don’t drain well," says Raboine. Create a few planting zones based on how much and how long the soil stays moist, then plant according to how well your plant's can handle that moisture.