Design

Here are some resources to aid gardeners building a rain garden in their backyard. 

Rain Garden Homeowner’s handbook. How-to instructions.

The Master Rain Gardener online video course. In-person classes also available.

Master Rain Gardener Facebook Group - to post plans, and see other people’s solutions.

Set up a one-on-one personal rain garden consultation with our staff. 

List of Certified Rain Garden Contractors - these folks know how to build rain gardens. If you need help digging, or planting.

Rain Garden plant list - vetted by local gardeners. These plants will thrive in your rain garden!

Where to get native plants for rain gardens in Washtenaw County.

"The Washtenaw County Water Resources people were great... For me, it was an easy choice... an opportunity to experiment with a new way of gardening and help the environment."
- Fran Alexander, avid gardener and Allen Creekshed resident

Save Money on your Stormwater Bill

If you live in Ann Arbor, you can receive a credit on your stormwater bill if you build a rain garden. Check out how to get your rain garden credit here.

There are other ways to get a credit - by doing these simple environmental practices. Become a RiverSafe home. Install a rain barrel. Install a drywell or cistern. Install a rain garden. Check out all the ways to get a credit here. 

Tips and Tricks

You may know generally how a rain garden works. It is a bowl shaped depression in the ground shaped to puddle rainwater. 

First, the rain garden should be downhill from the water source. The water source is often a downspout, but it could also be some paved area like a driveway or sidewalk. Next, decide how the water will get to the rain garden. Will it be underground in a pipe you install? Or run over the ground downhill to the spot where the rain garden will be? Here is a handy calculator to figure out the slope of a pipe.  Decide where the rain garden will be.

The rain garden is dug to pool water at 6” deep. Make sure the bottom of the garden is flat so that water can infiltrate evenly throughout the garden. Then you’ll want to add in 2” of compost and till it into the existing soil. It is important to till in your compost so the two soil layers don’t remain separate. You can get a perched water table if you don’t till in the compost, and the plant roots won’t go down past the compost layer. Spread shredded hardwood mulch to keep plant roots moist and healthy. Those plant roots are really what is doing all the hard work of infiltrating storm water into the ground and out of your yard. 

 You generally don’t need gravel or rocks under the garden. By relying on the plants, the garden will work better and better as the roots become more developed. We also add 2” of mulch to reduce the amount of weeds. The mulch won’t take up any water storage capacity. 

The dirt that you dig out of your site can be used to level the bottom of the rain garden and to make a berm on the downslope side of your garden. So starting at the uphill side of the garden, you’ll dig down and start moving dirt to the downslope side, to create a flat ‘terrace’. Then you’ll create a berm so there is a lip holding the water from spilling over your terrace. For flat sites, you’ll need to move the dirt away from your rain garden so think about low spots in your yard that you would like to fill or other areas where you could put the dirt. It is likely that the dirt will need to be stabilized with grass or mulch. 

 You’ll need to create an overflow point in the berm. In a larger rain event, the rain garden will overflow, so you’ll want to make a notch, or a lowered part of your berm where you want to direct the water. So if you have a berm completely around the rain garden, lower one section of that berm to direct water away from your house or sidewalk. That lowered portion of the berm is really what is controlling the water level, so make sure that is 6” above the bottom of your rain garden. Make sure your rain garden isn’t located in the very bottom of your ‘bowl’ – otherwise the garden won’t be able to drain after a big storm, which can drown the plants. 

In terms of placement of your rain garden, the most important rule is that it needs to be at least 10ft away from any structure with a basement. It is also best to place the rain gardens outside of any existing tree line, but depending on the tree type, that rule can be bent. I often try to place rain gardens in a spot that is out of the way (so you can still use your yard for whatever you enjoy) but still visible so you can enjoy it! For your yard, it sounds like extending the existing garden bed to incorporate the wet area could be a simple solution. 

Below are a few plant recommendations that would work for your site. These are all neater plants that do well in part sun.    

Top 10 Rain Garden Plant List 

  • Blue Flag Iris- Spring| very reliable plant for wet sites 

  • Palm Sedge and Brown Fox Sedge- no bloom | these are bunched, low growing grass-like plant. I would plant a lot of these, and mix in the forbs in patches 

  • Canada Anenome- Spring and sometimes again in September | has little white flowers and is low growing. It spreads rapidly but the leaves will turn brown in July if they aren’t watered. They will always come back, even without water. It will hold up to being run over by dogs!  

  • Wild Strawberry- Spring | this is a low groundcover that I would plant all along the edge of your rain garden, the runners will start to creep a little into the grass and is fine getting stepped on.  

  • Nodding Wild Onion – Fall | neat bunching plant that has a delicate flower 

  • Black Eyed Susan – Summer-Fall | looks floppy when done blooming so best to dead head, spreads rapidly.