Where to Go with the Overflow (from your rain garden)

 In 2011 we had record rainfall in parts of Northeastern Illinois and our rain gardens have helped infiltrate a portion that would normally run-off into our local storm drains.  By using native plants, you are not only infiltrating more run-off but supporting wildlife too. Due to the excess rain, you might have experienced overflow from your rain garden during the heaviest or most saturating rainfalls or you might not have thought about overflow when planning your rain garden.   Rain garden overflow can lead to several problems such as erosion, slippery walkways, or a missed opportunity to infiltrate more rainwater. There are several ways to handle or reduce rain garden overflow. Here are just a few suggestions.

1. Size your rain garden to handle the amount of water expected. There are several helpful rain garden websites like Wisconsin’s DNR that give equations to calculate the size of your rain garden based on soil, amount of run-off and other factors.
2. Some folks create planted berms around their rain gardens then cut out an overflow channel or trench into the berm to allow overflow into a certain area. You can also locate your rain garden so that any overflow will occur toward the down slope, which is typically away from the house for most folks.  With any rain garden, it’s best to know what direction the water will overflow if it ever fills up.
3. Add multiple rain gardens if your existing rain garden overflows often and you have enough  yard area to do this  Adding another garden in series can capture the overflow of the original rain garden or adding a rain garden higher up from the original rain garden can intercept and absorb some additional moisture.
4. Add a bio-swale (gently sloped channel planted with native plants) to absorb some of the water coming into or overflowing from your rain garden.   Remember to observe your slope and overflow areas before adding a bio-swale and choose plants that will take the moisture conditions of your bios-wale.
5. Try to locate your rain garden in a sunny area or part sun area and use prairie (full sun)  native plants. These deep-rooted plants act like giant sponges underground and aerate the soil deeply. Part sun or shade loving native plants help absorb run-off too,  so don’t worry if you  don’t have enough sun.  Every little bit of infiltration helps.
6. Expand your rain garden, make it bigger.  Normally I suggest that folks observe a rain garden before it is planted a few times during several types of rainfalls. If you see it overflow during an average rainfall, you may want to make your rain garden a little bigger along with any other adjustments (adding amendments, leveling, adding an overflow channel, etc).  Of course, once you add plants, infiltration will certainly improve, but it’s easier to make adjustments to your rain garden when there aren’t any plants.
7. The easiest thing to do is add a garden of native plants surrounding your rain garden or on the down-slope or up-slope of your rain garden. The will absorb even more rain water coming into or overflowing from your rain garden. Remember a rain garden doesn’t necessary have to be an isolated area but can be integrated into your existing garden or a new garden so it blends aesthetically and functionally.

Please feel free to share with us and other readers how you have handled rain garden overflow, so that we can all learn and make improvements to our rain gardens.  If you have a photo or video to share about this subject, please place it on a photo or video sharing website such as Flicker or YouTube, and then include the link to it in your comment along with your comment. Thank you! Denise Sandoval, [email protected]