A rain garden is just what it sounds like—a garden to soak up rain water. It is a recessed
planting bed, shaped like a saucer or shallow bowl, designed to collect runoff from driveways, roofs, and other hard surface or sheet flow of rain from lawns. The collected water
is then infiltrated into the ground instead of running off to the lake.
Rain gardens are planted with hardy, water-loving native perennial plants that have deep
roots, which along with the soil, work to provide a filter system to catch pollutants such
as phosphorus, oil, mercury and other heavy metals in rainwater that run into the garden
area. Rain gardens allow sediments that are carried with runoff to settle so plants can
absorb the nutrients.
During a rainfall, the highest concentration of pollutants is during
the first inch, or first flush of a storm, which is retained in the rain garden.
In general, typical rain garden should be located at least 10 feet from the house and will
range from 100 to 300 square feet in size with a depth of 6 inches to 12 inches. As a
rule of thumb, one garden will handle the runoff from a hard surface that is about 10
times their size. For larger surfaces, more than one rain garden may be needed to handle
the runoff, perhaps locate one rain garden near each down spout. Rain collected will
infiltrate into the ground within a few days, sometimes even hours depending on your
soil type.
To be effective, rain gardens must be properly designed for the right shape and size to
accommodate the amount of roof, driveway, and other hard surfaces on your property as
well as your soil conditions. Plants must be used that are appropriate for your soil type
and will also tolerate standing water for up to 48 hours.
For proper design, it is recommended to consult resources to help you determine the
proper plants and dimensions. Talk with the local extension agent or a landscaping
professional knowledgeable about rain gardens or do an internet search for amazing resources.
