Reduce Runoff With Rain Gardens

Rain gardens are shallow, vegetated basins that collect rainwater from roofs, driveways, and streets and allows it to soak into the soil instead of becoming runoff on impervious concrete. Most rain gardens are 100-300 square feet. They are typically planted with grasses and flowering perennials. The rainwater waters the plants in the garden, and the pollutants in the rainwater are filtered out by the soil. It does this by evaporating and transpiring stormwater, mimicking natural filtering processes. Rain gardens can also serve as a source of food and shelter for birds, butterflies, and other wildlife. 

In some areas, stormwater is such a serious issue that creating a rain garden may qualify for tax credit! Here’s how you can build one at your home, school, or community!

Step 1: Test your soil

Not all soil types are suitable for rain gardens. After it rains and the soil where you want your garden to be is saturated, dig a hole six inches deep with a six-inch diameter. Fill it with water, let it drain, and then refill it. Wait 24 hours and see if the water is gone. If it is, then a rain garden can be built there!

Step 2: Consider a location

• Keep the garden 10-15 feet away from your home so water won’t seep into the foundation

• Don’t put the garden over septic systems or underground utility lines. To determine the location of these, call 811 before you dig out your garden. They will send someone out to mark them for you.

• Don’t position the garden in an area that is always wet, as the water absorption rate there will be too slow.

• Try to position the garden so that it collects stormwater before it reaches streets and sewer drains.

Step 3: Prepare the area

• As a general rule, the depression you dig should be twice as long as it is wide. If you need help deciding the dimensions, ask your local extension service agent for advice.

• If your soil contains a lot of clay, you will need a larger rain garden. If you have sandy or loamy soil that absorbs water quickly, make your depression 8-10 inches deep.

• Position the garden in a natural low spot that fills with water after a storm and gets half to a full day of sun. Place it so the long side faces uphill.

• Avoid putting the garden under a tree so that you don’t damage tree roots while digging.

• Remove grass and weeds from the site before digging.
   

Step 4: Making the garden

Get ready to dig! Most rain gardens are six to eight inches deep, with the deepest part in the center.

• Angle the sides of the depression so that they slope towards the center. The depression should be shaped like a saucer.

• If you would like to add compost, add it at this point. First, dig deeper to accommodate for the compost, then add it. For instance, if you would like a rain garden six inches deep but want to add two inches of compost, then make the depression eight inches deep to accommodate.

• Use removed soil to make berms, or low walls, on the downhill side of the depression. If desired, make berms on the other sides of the depression as well. The berms will prevent water from spilling out until it can be absorbed by the soil. Make the berms six to eight inches above ground level. Then, pack the berms down. You can also use landscape fabric to hold the berms in place.

• Mulch around the plants and berms or cover them with rocks or stones to control erosion. Don’t mulch with pine bark or wood chips, which will float away.

• Use decorative rocks or stones to line the sides of any trenches to direct the water to the rain garden.

Step 6: What to Plant in Your Rain Garden

Grow plants adapted to your area, like wildflowers and other native, low-maintenance plants. Native ornamental grasses and sedges are a good choice to hold soil in place with their strong root systems.

• Start with plants that have well-developed roots, since seeds will be washed away by stormwater.

• Put plants that like wet conditions in the deepest areas of the depression.

• If there’s not enough rain, give the plants an inch of water a week until they’re established. 

Sources: US EPA 2021, USGS 2021, Home Depot 2021

Photo from Unsplash