Rain garden and attractive way to handle stormwater
Managing stormwater is a difficult and expensive challenge, particularly in the built environment of urban areas such as Greater Columbus, where so much of the environment is covered with impervious surfaces such as streets and driveways, buildings and other structures, parking lots and other hard surfaces that prevent heavy rains from infiltrating the soil and recharging groundwater.
A changing climate that produces storms with a greater intensity of rainfall only adds to this challenge.
Homeowners can install small rain gardens in their yards to reduce stormwater runoff from paved areas such as driveways, sidewalks, patios or from downspouts, which overflow and cause erosion during heavy rainfall events.
What is a rain garden?
A rain garden is built into a shallow depression in the ground, which traps stormwater from rainfall or snowmelt and allows the water to infiltrate the soil and recharge groundwater supplies. Rain gardens are typically planted with flowering herbaceous perennials, shrubs, grasses and even trees that thrive in moist soils and do not require frequent maintenance. Plants suitable for rain gardens typically have deep root systems, which helps water to infiltrate through the soil and allows the plant to thrive in periods of low soil moisture.
Benefits of rain gardens
Rain gardens provide a natural way to utilize heavy rainfall as a resource rather than a waste product that enters the local stormwater sewer system. They are designed to keep stormwater and its pollutants out of creeks, streams and rivers by providing a location to
hold excess water until it infiltrates into the soil.
Rain gardens can absorb 30% more water than the same area planted with lawn grasses and can remove or degrade contaminants in stormwater through microbial processes, and uptake and absorption by plants in the rain garden.
Rain gardens can also help recharge local groundwater supplies by temporarily holding stormwater until it moves through the soil profile, thus preventing excess water from entering already swollen surface waters via stormwater sewer systems. Plants in rain gardens can provide habitat for small wildlife and a food source for pollinators, butterflies and beneficial insects that support
songbird populations. And rain gardens can be a beautiful addition to any home landscape, providing seasonlong color from a variety of plants that flower at different times of the year.
Designing a backyard rain garden
Rain gardens should be located close to the source of water runoff and at least 20 feet away from the foundation of any structure. Rain gardens are most easily constructed on level ground, as sloped land and a steep grade will require excavation to create a level basin for the garden. The specif
ic soil characteristics of your site, which determine how quickly soil drains, will determine the proper depth for a rain garden.
To determine the depth, dig a test hole 8 inches deep in the location where the garden will be located. Fill this hole with water and let it drain. After the water has drained, fill the hole with water again. After 24 hours, measure the depth to which the water has drained. This depth in inches is the depth to which the rain garden should be dug from the surface of the soil.
To determine the proper size for your rain garden, measure the drainage area of the impervious surface that will supply the water for your garden. This might be the roof of your house or a paved patio, or even the driveway. Then divide the total square footage of your drainage area by the drainage depth of your test hole to determine the number of square feet that should be in a rain garden for your site. A typical backyard rain garden will be between 100 and 400 square feet.
Choose native plants
Consider using native plants in your rain garden as these plants are bestsuited to local conditions and support native insects, pollinators and wildlife. Many native plants have deep root systems that help channel water deep into the soil and also require little maintenance or supplemental watering.
When choosing flowering perennials, be sure to include a variety of plants that flower at different times of the season for maximum color. The yearly flower show in our rain garden on the Ohio State University campus starts with the stately blue flag iris in May and closes with brilliant New England asters that flower in September and October. A fullcolor Guide to Native Plants for Rain Gardens is available at go.osu.edu/nativeraingardenplants.
Sources of assistance
Technical and financial assistance for the design and implementation of rain gardens is available from the Franklin Soil and Water Conservation District (SWCD), which operated the Central Ohio Rain Garden Initiative and will offer a Master Rain Gardener training program for landowners this fall. For more information, contact Franklin SWCD at 614-486-9613. A free rain garden handbook is available from Ohio State University Extension at go.osu.edu/raingardenhandbook.
Mike Hogan is an associate professor at Ohio State University and an educator at the OSU Extension.
hogan.1@osu.edu