Rain gardens invite birds and butterflies while replenishing groundwater
The past couple of rainy springs have revealed a spot in our yard that remains wet much longer than the rest of the yard. Instead of bringing in topsoil to raise the area and encourage water to head toward a drainage ditch, I am considering creating a rain garden.
Rain gardens are small depressions planted with deep-rooted shrubs and perennials that hold rainwater, allowing it to infiltrate into the ground and replenish groundwater instead of running into storm sewers or drainage ditches.
The area where my rain garden would be located is in an ideal spot. First, it is sunny. Many of the plants best suited for rain gardens are sun lovers. Next, it is about 20 feet from the corner of our house. Rain gardens should be kept at least 10 feet away from a home.
And, it has several ways to capture excess rainwater: a downspout directs water this direction; the overflow from our pond heads this way; and the ground slopes toward it. Where a sump pump empties water, driveways and swales are other possible sources of runoff.
Also important, the area has no utility lines near it, and it is not over our septic field. Always call JULIE, an agency that marks the location of underground electrical and gas lines, before digging so a rain garden project doesn't turn into a large repair bill or a trip to the hospital.
A rain garden, itself, should be as level as possible. Rain gardens being constructed on level ground only need to be about 5 inches deep. My area slopes to 8 inches deep, so it is more appropriate. Use the excavated soil to create berms along the garden's edges to direct excess water.
Like most northern Illinois gardens, my soil is clay filled, but it drains at least 6 inches of water in a day. A simple test will ensure the soil is suitable for a rain garden. Dig a hole at least 6 inches deep and wide in the area where the garden will be located and fill it with water. Monitor the drainage. If the water is gone in a day, the location is appropriate. If not, either try another area or plan to dig the garden deeper. Add a layer of coarse gravel on the bottom and amend the soil with organic matter.
Rain gardens that drain properly are not breeding grounds for mosquitoes. The water drains before they can breed and their eggs can hatch.
The size and shape of rain gardens vary depending on the amount of water available and personal taste. The most important design consideration is that the garden fits in with the style of the rest of the landscape, that it looks like it belongs.
Planting the perennials is the fun part! Choose native plants with deep roots that dive as much as 10 to 20 feet into the soil, channeling rainwater deep into the ground and allowing plants to withstand dry periods in summer. Native plants also create a paradise for birds, butterflies, bees and other pollinators.
Site plants in a rain garden according to their moisture requirements. Those that need more water should be planted toward the center in the deepest part; those that prefer less moisture should be positioned on the edges. There are many magnificent tall plants perfect for rain gardens, such as Culver's root, cup plants, ironweed and Joe Pye weed, but shorter options like bee balm, black-eyed Susan, blazing star, coneflowers and swamp milkweed are more suited to the area where my rain garden will be located. In addition to bodacious bloomers, consider including grasses and sedges. They grow beautifully in rain gardens.
Just as in other newly created gardens, the plants in a rain garden require extra attention their first year. Give plants an inch of water each week if rainfall does not supply it. A layer of shredded hardwood mulch will help keep the soil moist.
Rain gardens are not the answer to flooding problems, but they do reduce the amount of rainwater running to sewers or ditches, recharge precious groundwater and invite birds, bees and butterflies to the landscape.
• Diana Stoll is a horticulturist, garden writer and speaker. She blogs at gardenwithdiana.com.