How to make a rain garden

A rain garden is a shallow hollow that captures stormwater runoff. The rain garden is planted with plants, trees and shrubs that allow runoff to soak into the ground. A rain garden can help protect water quality as well as beautify your landscape.

Instructions

1. Choose a location for the rain garden. It should be at least 10 feet from the house, in partial to full sun. Don't place over a septic system or near underground utilities or wells. Don't put it in a spot that tends to catch water already, since water infiltration is slow in existing wet patches. The water in the rain garden should be
   absorbed after several hours.

2. Find the slope of the site to figure out how deep the rain garden should be. Hammer stakes at the downhill and uphill ends of the rain garden site. Tie a string to the bottom of the uphill stake and run it to the downhill stake, checking for level with a string level. Measure the width between the two stakes and the height between the ground and the string on the downhill side. Divide the height by the width. Multiply this number by 100 to find the slope percentage. If the slope is between eight percent and 12 percent, make the rain garden eight inches deep. If it is between five percent and seven percent, make it six to seven inches deep. For slopes less than four percent, make the rain garden three to five inches deep.

3. Identify the lawn's soil type: clay, silty or sandy. Clay soil is sticky and clumpy, silty soil is smooth, and sandy soil is gritty. Clay soils have the slowest filtration, so a rain garden in this type of soil must be slightly bigger than those in other types of soil.

4. Dig the rain garden, placing the soil around the edge to form a berm. For a steep lawn, fill in the lower part of the rain garden with soil from the uphill part and bring in extra soil for the berm. Lay string around the perimeter to mark the edges, and use stakes with strings tied at ground level on the uphill slope. Dig to the correct depth by measuring the distance from the string to the bottom of the hole.

5. Plant trees, shrubs, flowers and other plants. Use native species of plants that have large root structures and are resistant to pooling and dry periods. Use mature plants with developed roots rather than seeds.

6. Determine the size and shape of your rain garden. Rain gardens are typically between 100 and 300 square feet. The length of the rain garden should run perpendicular to the downspout and slope to catch as much water as possible, and wide enough for water to spread evenly. It should be twice as long as it is wide, to a maximum width of 15 feet.

Resources

• A brochure with detailed instructions for building a rain garden can be found at The Wisconsin Department of Natural Resources' website.