Create a Rain Garden, Utilize Rain Run-off from Roofs, Driveways

Last Updated on July 30, 2020 by Kimberly Crawford

Rain gardens use run-off from roofs, driveways, other impervious surfaces. Rainwater is used by native plants rather than running to the storm sewer or ditch.

A rain garden is just that – a garden that utilizes the rain. It can be a personal contribution to cleaner water and an improved environment in a backyard and neighborhood.

It is a garden with a shallow depression to receive roof, yard, parking lot or street rain run-off. Rain gardens are being established in yards, boulevards, surrounding parking lots and more in urban and rural America. Many urban communities are working together to establish rain gardens in public and private areas.

Rain gardens increase the amount of water filtering into the ground to recharge the groundwater. They help reduce the amount of pollutants washing off imperious surfaces (roofs, sidewalks, pavement, street, parking lots) into lakes and streams via stormwater drains and ditches.

They are a beautiful way to showcase native plants, attracting birds and butterflies. Some shrubs are used, but the focus is on native perennial flower species.

A rain garden is not a pond. It is a depression that allows rapid infiltration into the soil, so there is not standing water for long periods of time. Therefore, they are not a breeding ground for mosquitoes. Mosquitoes need 7 to 12 days of standing water; it is only standing in the rain garden depression for a few hours at the most.

In this article

Why Plant a Rain Garden

Rain gardens help prevent flooding and drainage problems.
Rain gardens protect streams and lakes from contaminants, manage the amount of water reaching surface waters, and help reduce erosion of streambanks and lake shores.
Rain gardens reduce the load on municipal storm water treatment structures.
Rain gardens provide habitat for birds, butterflies and beneficial insects while enhancing the beauty of the area.

Considerations Before Creating a Rain Garden

Locate the rain garden at least ten feet from the house foundation so infiltrating water will not seep into the foundation.
Do not place over the septic system or a sewer pipe.
Watch how rain drains off the roof; it may be most effective to select the side of the house with the greatest run-off.
Integrate the rain garden into the full landscape of a home as would when considering any new flower bed.
If establishing a rain garden to service a parking lot or boulevard, work with the community authorities before siting the garden.

Design the Rain Garden

Many resources exist to help design and plan a rain garden. Much research has been done by University or Wisconsin Extension Service and the Wisconsin Department of Natural Resources, which have resulted in some excellent resources for rain gardens.

Check with the Cooperative Extension Service, the USDA Natural Resource Conservation Service, county Soil and Water Conservation Service or greenhouses and nurseries for local resources.

Use these resources to accomplish the steps:

Locate a proper site.
Calculate square footage draining to the rain garden from the roof, yard, driveway, parking lot, etc.
Use this information to size the rain garden. Generally, rain gardens are about 10% of the drainage area. For example, if the drainage area is 500 square feet, the rain garden will be roughly 50 square feet, although it can be any shape.
Use information about soil types and the size needed to determine the depth and slope of the depression by evaluating soil compaction, soil type and texture, rate of water infiltration into the soil. In heavier soils, a deeper depression is often dug and sand is added to facilitate drainage.
Add the appropriate spaces for surrounding upland (drier) plants to complement the plants in the depression.
Use rope to mark the shape and size of the rain garden. The resources indicated above include some basic design plans as a good starting point.
Many people have the resources to construct their own rain garden; others need to hire a landscape contractor.
The first step is to dig the basin or depression, then create the berms, and prepare the entire bed for planting. Finally, the garden is planted with bedding plants (seeds may be used in the upland areas), mulch is added.
A rain garden needs to be watered until it is established. If appropriate native plants have been used, additional water should only be needed in times of drought. Fertilizers should be used to get the garden established, and every spring thereafter.

Rain Garden Plant Selection

Begin plant selection with native species of perennial flowers, grasses, shrubs or small trees that fit the USDA Hardiness Plant Zone for the location.
Consider plants with deep root systems to encourage infiltration of run-off water.
Native species are adapted to local conditions, so are more resistant to diseases and better adapted to the local climate.
Consider the soil types in the rain garden and the amount of sunlight received each day.
A diversity of plant types, colors, shapes and textures will provide interest and attract a variety of wildlife.
The resources listed above contain sample plant lists; check catalogs and local plant nurseries for ideas.

Maintain the Rain Garden

Once the rain garden is established, very little additional water or weeding is needed. Rain gardens can be cared for similar to other perennial flower beds featuring native species.