How to Make a Rain Garden in Your Yard—and Why You Should

Rain can be great for your garden. However, large storms can be a problem. Heavy downpours can run off roofs and driveways, collecting pollutants like oils and fertilizers, along with garbage, and then enter storm drains and flow directly into nearby streams and ponds.

Fortunately, there's an elegant solution to keeping that water out of the storm system: a rain garden. These shallow, planted depressions capture and absorb stormwater runoff, filtering it through soil and plant roots before returning it safely to the ground. In doing so, they ease pressure on municipal storm systems, limit localized flooding, improve local water quality, and create habitats for birds, butterflies, and other pollinators. Here's how to build one. 

Scout a Location

Before choosing a location for your rain garden, it helps to understand the goal. "Think about what you're asking this landscape intervention to do," says Kelly Norris, an ecological horticulturist and landscape designer. "Plants in a rain garden act as green sponges, putting stormwater to use as it soaks into the ground.”

Start by identifying where the water already flows on your property. The ideal location is typically downhill from a roof downspout or another area that collects runoff. While you might be inclined to place the garden in a spot where water already pools, those areas often indicate poor drainage and slow infiltration, making them less suitable for a rain garden, says Benjamin Vogt, author of A New Garden Ethic.  

The garden should be at least 10 feet from your home's foundation, 8 feet from any well, 5 feet from a septic system, and at least 1 foot above bedrock or the seasonal high groundwater level. Avoid buried utilities or heavily trafficked areas.

Determine the Size and Shape

Most residential rain gardens are between 100 and 300 square feet and 3 to 8 inches deep. Before choosing a size, check the slope of your yard. Rain gardens work best on gentle slopes and should generally be about one-fifth the size of the roof or paved surface draining into them. The basin should be deep enough to hold about 3 inches of water during a storm. 

Dig the Basin

Begin by removing any existing grass. Once dead, cut and remove the sod with a sod cutter.

Next, mark the garden's outline with string or marking paint. Start digging from the uphill side of the site, excavating the garden to your desired depth—typically 3 to 8 inches. The goal is to create a shallow basin with a level bottom so water spreads evenly throughout the garden. On steeper sites, you may need to move soil from the upper edge to the lower side to create an even planting area. 

Use the excavated soil to build a berm, or raised mound. This helps hold water in place while it slowly soaks into the ground. 

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Determine Soil Type

Soil type plays a major role in how well a rain garden functions. Sandy soils absorb water quickly, while clay soils drain more slowly and may require a larger basin.

That doesn't mean clay soil is a dealbreaker. "Clay soils here aren't a bad thing, although you want to be mindful of how long water is ponding," Norris says. "The idea is to simply slow it down, but keep it moving."

To determine your soil type, dig down 4 to 6 inches and collect a handful of soil. Add a few drops of water and squeeze it in your hand. If it crumbles apart, it's sandy. If it forms a short ribbon before breaking, it's silty or clay. If it forms a ribbon longer than 2 inches, then you may need to amend the soil before proceeding.

Choose the Right Plants

Native plants are often the best choice for rain gardens because they are adapted to local conditions and typically develop deep root systems that help absorb and filter stormwater.

When selecting species, Norris recommends looking to naturally wet habitats. Because these plants evolved in places where water levels fluctuate, they are often well-equipped to handle both temporary flooding and dry spells.

The other secret to a successful rain garden? “Plants, plants, and more plants,” says Claudia West, principal of Phyto Studio, a landscape architecture and horticultural consulting firm. While mulch can help young plants become established, she says it is the vegetation itself that does most of the work. Deep roots create channels that allow water to move into the soil, while leaves help return moisture to the atmosphere via evapotranspiration.

A full planting not only improves the garden's ability to manage water but also helps suppress weeds, stabilize soil, and reduce maintenance over time. Dense planting doesn't have to look wild or unkempt, West notes. Thoughtful combinations of flowering perennials, grasses, and foliage plants can create a garden that is both visually appealing and highly functional. “The result is a garden that is beautiful, hardworking, and durable—a landscape that manages water naturally and fits into our busy lifestyles,” West says.

Vogt also recommends paying attention to how water moves through the site. “If we identify a lower area in the landscape where water collects or even runs through, we'll use species that are adapted to periods of more moisture,” he says. “In the case of a place where water flows through and we want to slow it or absorb it, we plant with fibrous roots that can drink more, while also opening the soil more.”