If you're interested in a rain garden, chances are you probably have a site picked out. If you are not sure yet, here are a few points to consider as you think about location:

• Keep the garden 10–15 feet from foundations
• Don't put it over a septic system
• The best spot in your yard is NOT that soggy low spot—the best rain gardens drain quickly!
• Know your soils and plan accordingly. Sand drains best, and clay drains poorly.

There are two main schools of thought when it comes to rain garden design:

1. The technical: analyze, measure, assess, calculate, predict, prepare, and carefully implement
2. The guess and check: "seems like rainwater will go this way, let's dig a hole and fill it up with plants!"

Both styles have their time and place, and for many rain gardens on a homeowner's property, the "guess and check method" will work just fine. That said, if you're dealing with heavy volumes of rain or you're thinking about using a rain garden for erosion control, then we strongly recommend using the technical approach; a poorly planned rain garden could lead to a wet basement.

Here, we avoided the risk of water damage to the building's foundation through a "buffer-style" rain garden that drained away from the building. We placed rocks around the drain to allow more time for the rain garden to take care of the storm water.

If you are interested in getting a more in-depth overview of rain garden design, here are some more resources:

Washtenaw County

Washtenaw County has a well established rain gardening website including an opportunity to take their Master Rain Gardener Class.

Wisconsin Department of Natural Resources

The Rain Gardens manual from the Wisconsin Department of Natural Resources is a more simplified guide on installing rain gardens, and it includes some nice design drawings to help stimulate your creativity.

Sizing

To retain the volume of water associated with most rainstorms, try to make a rain garden about one fifth (20%) the size of the area it's draining, assuming a depth of 6 to 12 inches. So if your roof is 20 feet by 50 feet (1000 square feet), then your rain garden should be about 200 square feet in area (a 10 by 20 foot rectangle, or a circle with a 16 foot diameter).

Remember: you can still install undersized rain gardens if you account for the flow of water through and out of the garden. Once this rain garden fills up, storm water simply drains past it--on to a storm drain or to the lawn behind the garden.

Removing sod

Once you've got a feel for the location, size, and design of your rain garden, you should feel an overwhelming urge to remove some sod and dig out a basin. You can do this with a shovel by digging through the grass's shallow root system and rolling it up, or you can rent a sod cutter for large areas.

Weeding

If you are removing sod to install your garden, chances are there will be very few weeds. However, if you are installing a rain garden in an area that didn't have lawn, was overgrown, and/or full of weeds, you'll need to remove the weeds (with a careful application of herbicide or by hand pulling) and wait for the seed in your freshly weeded bed to germinate (this is called flushing the seed bank). It may look nice after you weed it initially, but don't be fooled—there are weed seeds in the soil. Flushing the seed bank a few times will ensure that you don't find yourself overwhelmed with pesky weeds after you plant your rain garden.

Plant selection

Michigan native plants have adapted to our conditions while also providing habitat needs for pollinators and birds. Consider using deep rooted native species in your rain gardens to improve absorption of stormwater and enjoy 4 seasons of variety and beauty. Use plants adapted to the conditions of your site: sun/shade, sand/clay, wet/dry. This chart from the Calvin University Ecosystem Preserve may help get you started with the variety of plants to choose from. There are local native plant sales offered several times a year through the Calvin University Bunker Interpretive Center, River City Wild Ones, Kent Soil and Water Conservation District, and through growers with Native Plant Guild. We grow a large variety native plants in our greenhouse as well.

Extras

A few extra items may help the rain garden flourish quickly. Mixing in a small amount of compost with the native soil will give the plants a little boost to get established. Wood chips spread over the soil before planting will help smoother weed seed from sprouting. They are not necessary to re-apply every year as they will suppress native seeds from sprouting too, but along the edges of the garden they will add a more formal look. Finally, optional rocks, fencing, or garden decorations will communicate that this is an intentional garden and not a wild patch of weeds.

Sediment traps

Some rain gardens (especially curb cut rain gardens) may filter lots of sediment and other debris from stormwater. Homeowners will need to keep those sediments cleaned out of their rock channels to keep them draining quickly. There are various models of sediment traps, feel free to download our simple plan here.

Initially, rain gardens will need periodic watering until the plants are established. Keeping an eye on the plants will also help you identify weeds that begin to show up. Becoming familiar with both the native plants and the non-native plants will make the ongoing weeding over the years easier. As the native plants become established they will keep the weed population down to an occasional chore, and watering and fertilizing shouldn’t be needed.

Consider joining our Rain Garden Maintenance Facebook Group to ask questions and post pictures.

Rain Garden Maintenance Workshop presentation is available here for more information including sediment trap instructions.

This Rain Garden Maintenance booklet is prepared for homeowners as part of a grant-funded project to install 60 curb-cut rain gardens in Southeast Grand Rapids. It may be useful to you as well as it walks homeowners through three years worth of maintenance tasks to help the gardens reach maturity and health. The document takes a moment to open, but great things come to those who wait.

Performance Evaluation of Permeable Pavement and a Bioretention Swale (Toronto and Region 2008)

Effectiveness of Retrofitted Roadside Biofilter Swales - County Court Boulevard, Brampton (Sustainable Technology 2018)

Performance Comparison of Surface and Underground Stormwater Infiltration Practices (Toronto and Region Conservation 2015)

PCS Maintenance Guide