A rain garden (also sometimes called a raingarden or a water garden) is a bioretention garden that is built in a shallow depression on your property and provides a simple yet effect method for controlling stormwater run-off. Strategically placed, rain gardens intercept and collect water that runs off roofs, driveways and yards and allow it to infiltrate the soil rather than to run off into storm sewers. Because this type of garden acts as both a natural biofiltration system and a temporary water reservoir, rain gardens are able to significantly reduce the amount of contaminated storm water that has direct access to our lakes, streams, and rivers.
Rain gardens are built using a variety soil types (from clays to sands) and the size of the garden varies depending on the area drained and available space. They are designed to capture and treat run-off, however what rain gardens are not, are ponds. Although both are designed to collect and hold water, a rain garden is designed to collect and hold water for only about 6 hours after a storm — not longer.
Rain gardens promote sustainable design practices while encouraging environmental stewardship and community pride. Not only do they provide stormwater control, but they are also an aesthetically pleasing landscaping and a natural habitat for butterflies and birds.
When building a rain garden, Jim Hole from EnjoyGardening.com offers some great tips:
Location, location, location
Not surprisingly, a rain garden is typically placed where it will collect the most amount of runoff. For example, it can be located on the downhill side of a paved surface to reduce the amount of water that enters the sewer system or positioned near the discharge end of your downspout. But the most important thing to remember is not to locate a rain garden closer than three metres to your home. Basements make lousy bio filters, and I can guarantee that you won’t give a damn about the environment when you are pumping water out of your house. On that note, rain gardens built in spots too low to drain will also become poorly designed water ponds.
One size fits all
When planning the garden’s construction, the first principle to remember is that any sized rain garden is better than no rain garden at all. However, if you want to take a scientific approach to minimize rooftop runoff, start by calculating the size of your roof. For example, let’s say that your roof is 186 square metres and that rainwater runs to each corner equally. That means that each of the four down spouts drains about 46 square metres of roof. Next (stay with me now!), divide the 46 square metres by 6 (because someone somewhere discovered that was the magic number) to determine the optimum size of garden you need, which in this case is about 8 square metres.
The construction is relatively simple. Choose a location that’s not on too steep of a slope (this will eliminate erosion), dig the garden to a depth of 15 cm and ensure that you have well-drained soil—the sandier, the better. A good way to test your soil for drainage is to dig a 15-cm deep trial ‘pit’ and to fill it with water. If it drains within 24 hours, you’re set. If water remains after 24 hours, either replace the soil or amend it with a mixture of coarse sand and loam. The only step that’s left after that is to plant the entire rain garden (not just the periphery) with suitable plants.
Check out the Canada Mortgage and Housing Corporation (CMHC) website with great step-by-step instructions on how to design and build your own rain garden.
Or download a copy of Rain Gardens: A How-To Guide for Homeowners (.pdf 3.08 MB), a great handbook that walks you through the different stages in designing and building a rain garden.
Native Plants for Rain Gardens
There are plenty of excellent choices of plants to include in a rain garden. For example, astilbe, iris and ferns thrive in rain gardens, as do dogwoods and nannyberries. In fact, the list of suitable plants is much larger than the list of unsuitable ones. We have provided some suggestions for native plants you may want to include. Click the appropriate link below for plants suitable for the wet soils in the center of rain gardens:
Canada Mortgage and Housing Corporation
City of Carter Lake Stormwater Management
Osceola-Lake Conservation District
Wisconsin Department of Natural Resources
Links to More Information About Rain Gardens:
Canada Mortgage and Housing Corporation (CMHC) - Rain Gardens: Improve Stormwater Management in Your Yard
City of Maplewood Minnesota - a great site with lots of information on building your own rain garden; also includes some great designs for different types of rain gardens
Harpeth River Watershed Association - information on rain gardens, including how to design and build one of your own
Plants for Stormwater Design - a publication from the Minnesota Pollution Control Agency that takes an in-depth look at how improve stormwater treatment and management practices by using native plants
Urban Water Quality - here find lots of rain gardening links, provided by the Urban Resources & Borderland Alliance Network