Rain Gardens: Helping Improve Water Quality One Backyard at a Time
Photo from Wisconsin Department of Natural Resources
As cities and municipalities grow and replace agricultural land and forests, increased storm water runoff from these developed areas ends up in storm drains. The water that runs off impervious surfaces such as parking lots, sidewalks, and rooftops carries with it pollutants like fertilizers, pesticides, grass clippings, road and sidewalk salt, and animal waste. Each homeowner can mitigate that runoff by installing a simple rain garden and reduce the runoff by about twenty five percent on their property.
Rain gardens are just that: gardens. They are not prairies, but are well planned out flower gardens, although some grasses might be employed. The first year, it may be necessary to keep weeds at bay until the plants mature and crowd out the undesirables. In subsequent years the garden is lower maintenance, but it will be necessary to thin out the population of some plants to allow others to thrive.
Rain gardens have many benefits, not the least of which is increasing the amount of water that filters into the ground and stays out of the water treatment plants. In addition, they help protect streams and lakes from pollutants, are aesthetically pleasing, provide superior habitat for pollinators and beneficial insects, and help protect communities from flooding and drainage problems. Each homeowner can make a small impact, leading to a substantial community and regional impact.
A rain garden must be carefully and thoughtfully planned and installed. Look for low, flat areas with a maximum 10-12 percent slope. Choose a location that gets runoff from a roof, sidewalk, or other impervious surface. Make sure it is at least 10 feet from a foundation, at least 5 feet from a septic system, and at least 5 feet from a well. Avoid underground lines, tree roots, and high traffic areas. Ideally, incorporate it into existing and future landscaping, taking into consideration views from inside any dwelling, the street, and recreational areas.
Do not choose a location that is frequently waterlogged. A rain garden is not a pond. The water should drain from the site in less than 24 hours, preferably in 2-4 hours. This feature will prevent the fear of mosquitoes breeding. (This pest needs 7-12 days to lay eggs and hatch.)
The size of your garden is determined by how much runoff you are collecting. Typical residential rain gardens are 100-300 square feet. A simple calculation would be to multiply the length and width of your home and divide by six. This will be a ballpark figure of a garden that will hold an inch of water at six inches deep.
Outline the shape of the garden, remove the turf, dig to the desired depth (typically 4-8 inches), keeping the bottom flat. Choose native plants that are suited to the soil type, sunlight, and location requirements of the garden. Put the most moisture tolerant plants in the center with ones that will tolerate drier conditions along the edges. Select varying bloom times, height, and colors for maximum wildlife benefit.
For more complete instructions on building the garden and plant selection, please refer to the Wisconsin DNR bulletin Rain Gardens a Guide for Homeowners and Landscapers ( https://widnr.widen.net/s/7zpg7qgpl8/raingardenmanual_hd )
Installing a rain garden takes some work initially, but the long-term benefits are well worth the effort. Gather some friends and make it a fun adventure.
Happy Gardening.
Carol Shirk
Certified Master Gardener