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Installing a rain garden

The four steps of installing a rain garden:

  1. Site selection
  2. Design
  3. Construction
  4. Maintenance

Site Selection

If you're interested in a rain garden, chances are you probably have a site picked out in the back of your mind. 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.

 

 

 

Design

rain garden design drawingThere 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'd strongly recomend using the more technical approach--Remember, a poorly planned rain garden could lead to a wet basement!

 

 

rain garden planting

We avoided the risk of water damage to the building's foundation grading this by "buffer-style" rain garden in a way 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.

 

 

 

There are scores of resources out there for you if you're interested in getting a more in-depth overview of rain garden design.

 

Washtenaw County has a well established rain gardening website with great tips and examples.

 

 

 

Michigan LID manual, Chapter 7The chapter on bioretention from Michigan's Low Impact Development Manual is a thorough and fairly technical guide to implementing rain gardens and other types of bio-retention projects.

 

 

Wisconsin DNR Rain Garden ManualThe Rain Gardens manual from the Wisconsin Department of Natural Resources is a more simplied guide on installing rain gardens, and itincludes some nice design drawings to help stimulate your creativity!

 

 

Sizing:

To retain the volume of water associated with mostrain storms, 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).

wet rain 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

Remember: you can still install undersized rain gardens if you account for the flow of water through and out of the garden.

Site preparation, construction, and planting

Removing sod

Sod removalOnce 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 spade/shovel by digging through the grass's shalow root system and rolling it up, or you can get rent a sod cutter (better for large areas) and make quick work of the grass.

Not dealing with sod?

The nice thing about putting in a rain garden in place of lawn is that as you remove the sod, a lot of the weed seed goes with it. If you're 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! And "flushing" the seed bank a few times will ensure that you don't find yourself overwhelmed with pesky weeds after you plant up your rain garden.

Plant selection

Check out some sample rain gardens at Washtenaw County's Rain Garden Page:

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.

Maintenance:

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 raingardens 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.