Below you’ll find two step-by-step design manuals for Michigan Rain Gardens. Each takes a different approach. Pick the one that best serves your needs. Look further down below for a brief, basic orientation to help you get started.
Installation tips below adapted from the Washtenaw county Master Rain Gardener program, created by Susan Bryan, Harry Sheehan and Shannan Gibb-Randall.
The goal is to capture the first 1/2″ of runoff from a rooftop or driveway. A rain garden should be about a fifth of the size of the rooftop or paved area draining to it and be deep enough to pool 3″ of water. For instance, if you have 500 square feet of rooftop draining to a downspout, the garden should be 100 square feet (10×10) and 3″ deep.
Rain gardens are intended to infiltrate rain water to the ground, not into your basement. Gardens should be located downhill and at least 10 feet away from your foundation (and your neighbor’s!)
Expect to pay $2/square foot if you do it all yourself, $5-8 if you hire a landscaper to dig, $15 if you hire out the design and construction. Prices vary widely.
The water in your garden should infiltrate into the soil within 24 hours of a rain. To test your soil, dig a hole 18″ deep and fill it with water. Let the hole drain once, and then refill it. As the hole drains for the 2nd time, time how long it takes. If it takes more than 24 hours, hire a landscape contractor.
Chronically wet locations are not well suited for rain gardens since they don’t infiltrate well. Native wetland plants such as ferns, iris, milkweed, and blazing star, will help absorb water in these locations.
Topsoil and compost, if needed. Use your judgment like you would for any perennial garden. Good soil and compost make all plants happy, and improve infiltration in tight soils. Always mulch to reduce weeds and evaporation during dry weather. 2″ of compost and 2″ of mulch make sense for most gardens
If you direct downspout water to the garden via pipe, have it surface above the 3″ pool so water and decaying material don’t clog the pipe. This may mean digging your garden deeper. However, you may have enough slope to have it enter the rain garden on the uphill side, yet still be above the 3 inch pool.
Rain gardens are designed to overflow during heavy rains. Make sure it will spill over to a safe distance from sidewalks, property lines or retaining walls.
Expect to water regularly for the first season to reduce mortality and speed root development. After the first year, native plants need only be watered during very dry weather. Weeding is also most critical in the first season or two. After that, weeds should compete poorly and will likely appear at the edges.
This project has been funded in part through the Michigan Department of Environmental Quality’s (DEQ) Nonpoint Source Program by the United States Environmental Protection Agency (EPA). The contents of the document do not necessarily reflect the views and policies of the EPA or the DEQ, nor does the mention of trade names or commercial products constitute endorsement or recommendation for use.