How to Make a Rain Garden

Gardens can be more than beautiful—they can provide food, shade your house or your yard, and they can even help draw flooding away from your house. Rain gardens are sunken areas in your landscape, specially created and planted to help contain and handle excess rainfall.

Rain gardens not only help reduce your risk of flooding, but they can help reduce water pollution in your community too. As the water flows through your rain garden, it filters off pollutants and debris that would otherwise go directly into local streams and waterways.

Even in the driest parts of the country, a rain garden can help with the fluctuations in rainfall (and can even help recapture excess rainfall, a boon in areas experiencing drought). The rain garden design just needs to be pegged to the local environment.

"Regardless of location, a well-planned rain garden will take into account the intensity and frequency of precipitation," says Coleman Cosby, project manager at the online landscape design company Yardzen. "Property details, slope, garden size and depth, plant choices, and soil infiltration rates should all be considered to handle the type of rain events likely to occur."

Find the Right Spot

Because your rain garden is gathering runoff, you don't want it close to your house. Look for a spot at least 10 feet away from your house (and from your neighbor's house—you don't want to make flooding worse for them!). The spot should be on a down slope away from your house, but not the lowest point—you want another failsafe spot where water can continue to flow away from the house in the heaviest rainstorms.

Rain gardens are especially suited for spots near hardscaping like patios, driveways, or walkways, where it can help collect the water that runs off of those surfaces. Skip shady areas—you want somewhere with at least some sunlight to allow the area to dry thoroughly so it doesn't become a breeding ground for mosquitoes. And trees tend to be drainage powerhouses all their own, so don't place rain gardens beneath your trees.

If you're having trouble finding a good spot on your land, you can always opt for a mini rain garden, according to the Watershed Institute. A downspout planter siphons water away from your gutter system to water the plantings, then overflow drains out the bottom. (Just make sure that the planter area is set up and sloped so any overflow drains away from your house.)

Make Sure You Won't Hit Utility Wires and Pipes

You definitely don't want to damage your water and sewage pipes or electrical or gas lines when you're digging your rain garden. Call your local utilities to come out and mark line locations so you can steer clear of those areas.

If you have a septic system, you also want to keep the rain garden at least 25 feet away from the system, and higher than the leach field.

Test the Area's Drainage

"The depth of the depression needed for your rain garden will depend on how much runoff you expect and the type of soil you have," Cosby says. "You want your rain garden to absorb a typical rain within 24 hours. If your soil drains quickly, you can go deeper—if it’s poorly draining clay soil, you’ll want a more shallow depression."

Areas that can handle and drain 1.5 inches of water per hour are ideal, according to the state of New Jersey's rain garden manual. The best way to test? Dig a small test hole 12 inches deep and 4 to 6 inches wide, fill it with water once, then fill it again and measure how much it drains each hour for the next four hours.

Decide How Big to Make It

A lot of factors go into the decision of how large to make your rain garden, including the size of your plot, the amount of impermeable areas on your land (like your house, patio, driveway, pool, and sidewalks), the amount of rain you get, and whether the soil drains well.

For most homes, a rain garden 100 feet to 300 feet in width will be sufficient to manage water runoff, but even if you don't have that kind of space, any space helps. "For small properties, reduce the overall area of your rain garden so that it’s a safe distance from foundations and structures," Cosby says. "While you may not capture all rainwater in a smaller garden, you’ll still make an impact."

If your soil drains poorly, you will want to create a larger rain garden to offer more drainage, while you can use a smaller one if you have sandy, well draining soil. An ideal depth for a rain garden is between 3 to 8 inches, with deeper gardens in sandy soils, and shallower in clay soils.

Create Inlets and Outlets

Make it easy for water to drain away from your house by creating inlets that channel water into the rain garden. You can lay a stone swale to help draw water away from the areas with runoff into your rain garden, Cosby says.

Outlets are also helpful when big rainstorms happen—they'll help draw excess water from the rain garden and keep it moving further away from your home.

Placing rocks or berms of earth around the edges of your rain garden can help contain the rainwater and prevent erosion.

Max Out the Drainage With the Right Soil

If you have poorly draining soil in your rain garden spot, you can fix it. Add in a mix of coarse sand, loamy topsoil, and compost to create that perfect, quick draining soil that'll help your rain garden flourish.

Pro tip: Don't put down any weed block fabric in your rain garden, which could mess with your rain garden's drainage.

Choose Rain Garden-Friendly Plants

Obviously, this isn't the place for plants that love to stay dry! "Plants that can tolerate very wet soil conditions and wide fluctuations in soil moisture work best in a rain garden," Cosby says. "The plants in the basin, or lowest point, of the rain garden need to be able to withstand more moisture, and for a longer period of time, than those on the perimeter, which will dry out faster."

For your rain garden, look at native plants, which should thrive in your local climate. "They’re workhorses when it comes to controlling soil erosion, filtering pollutants, and allowing rainwater to return to the ground at a productive pace," Cosby says. Cosby recommends using varieties of Juncus or Sedges in the wettest part of the rain garden.

The National Wildlife Foundation's Native Plant Finder can suggest ideal native flowers, grasses, and shrubs as a great starting point. Choose perennials to minimize the upkeep on your rain garden.

Some common plants that are rain garden friendly include:

• Hostas

• Black-eyed Susans

• Coneflower

• Asters

• Holly

Tend to Your Rain Garden

Like other parts of your garden, your rain garden needs a little TLC to really thrive. Keep an eye on the plants, especially during long dry spells, to see if watering is needed, and weed it regularly to give your chosen plants room to thrive. (This is especially important in the first few years, before the plants really fill out and can help block weeds on their own.)

You'll also want to clear out any debris that could help prevent water flow—especially if you know a heavy rainfall is on its way. That way, nothing will keep your rain garden from fulfilling its duty.