What is a Rain Garden?
A rain garden is a garden with a shallow depression that captures runoff from impervious surfaces, such as rooftops, patios, driveways, and parking lots, before it enters the storm water system. Rain gardens can be customized and are limited only by the resources and time you want to put into them. They use natural processes to improve water quality by filtering pollutants and reducing the amount of storm water runoff. The water easily infiltrates into the soil because of the deep roots of the native plants and recharges the groundwater supply.
The Five Steps to Creating a Rain Garden
- Determine the placement, area, and depth of your rain garden. It can either capture runoff from your yard or downspouts and should be placed in between the water source and storm drain. Make sure it is at least 10 feet from your house and preferably in a sunny area. The area of your rain garden will depend on the area from which it is collecting runoff, either the size of your yard or roof. The exact equations for calculation can be found in the Rain Garden Manual. But if you would prefer to estimate, your garden should be about 8’ x 10’ if collecting from one downspout and 12’ x 26’ if collecting from the entire yard. To determine an exact depth, conduct a percolation test (details in the manual). Different types of soil drain at varying rates. Your garden should contain the water from a 1 inch rainfall event for 1-2 days. If you wish to skip the percolation test, a depth of 8 inches should suffice for most Lexington soil types.
- Outline the perimeter of the garden and prepare the site. The garden should be about twice as long as it is wide, and the longest side should be upslope to catch as much water as possible. Outline the perimeter using spray paint or a garden hose.
- Choose the plants and planting layout. Pick an assortment of native plants that bloom at different times and are varying heights. Plants that can tolerate wetter conditions should be placed in the middle of the basin and plants that like drier conditions should be placed on the outsides.
- Dig, level, and till. It is important that the bottom of the garden is level so that the water spreads out evenly. You can check this by laying down boards and using a carpenter’s level. Once level, till up to a foot of soil adding solid amendments if needed. Create a berm on the downslope side of the garden using the excavated soil to hold the water in. Add a spillway to allow the water to drain in the event of excess.
- Add in your plants along with 2 inches of soil, and enjoy your rain garden! For more details on each step and rain garden specifics check out the Rain Garden Manual.