According to U of I Extension Educator Duane Friend, when we receive rain, a lot of it falls on surfaces that cannot soak up water. Roofs and driveways create large amounts of runoff—much of which ends up in storm drains. It is estimated that water from these areas can increase stream flow by up to five times! Instead of allowing all of this water to uselessly drain away, one can create a place that will allow the water to drain back into the ground, away from the house. In addition, by planting the site to native perennial plants, it can add an aesthetically pleasing landscape to the yard. This is the idea behind a rain garden.
Friend says that a typical rain garden is an area that is 4 to 8 inches deep, with a flat bottom. The size of the garden will depend on soil type and the amount of surface runoff going into the garden, but for most yards it would need to be around 75 to 300 square feet in size. The shape will be influenced by such things as surrounding slope, and how it will retain water. A berm is built on the down slope end and sides to help keep water from running out of the garden. Rain gardens are designed to drain in an average of two days; so standing water, along with mosquito concerns, should not be a problem.
There are many native wildflowers that will work well in a rain garden setting. Native perennials do not need fertilizers and pesticides to thrive and, therefore, will not increase water quality problems. These plants have extensive root systems which will also take in large amounts of water as it percolates through the soil. It is usually best to start the garden with plugs instead of seeds.
Rural homes can also benefit from having a rain garden in the landscape. If designed properly, the garden can enhance the beauty of yards and neighborhoods, along with providing habitat for birds and butterflies.
For more information on rain gardens is available at https://extension.purdue.edu/rainscaping/.
To learn more, University of Illinois Extension horticulture educators Andrew Holsinger and Chris Enroth introduce the concepts and construction techniques of a successful rain garden, and what plants work best in rain gardens. The taped presentation is available on YouTube at https://www.youtube.com/channel/UCEYBGqFXZS6Sn37n1mVcY1g