While rain gardens are a pretty simple idea, there are a few things that should be carefully considered and planned if you decide to build one.
Choosing a site that is at least 10 feet from your home, not near any steep slopes or bluffs, or a septic system is key. You will need a minimum of 100 square feet of available space, maybe larger.
Rain gardens work best on well draining (or sandy) soils. Once you have a location in mind, be sure to test your soils to know how quickly the rain garden will drain, and help determine how big it should be.
Next you’ll need to consider how to get the water from your downspout, driveway or other area to the garden. There are many ways to do this, whether you bury a pipe or create a landscaped swale or channel to carry the water. Also, in case a big storm, or slow draining soils overwhelm your garden, make sure you have a safe place to send any overflow (across a lawn or vegetated area, out a pipe, etc.)
After you have carefully outlined the the shape and appropriate size, you can get dirty. The garden should be at least 18”- 36” deep. The bottom should be level and flat with sloping sides, like a bowl or a bathtub. Re-fill the hole with “rain garden soil mix” (mostly sand and compost), leaving 6” of ponding.
Choose your plants carefully. There are a lot of great plants for rain gardens, but some get to be very large, and others tend to spread. Take your time to select plants with the long-term look and feel you want to enjoy in your garden.
After your plants are in, add a thick mulch layer (3-4 inches thick) to help keep weeds down, and hold moisture in the soil. You will need to water the garden the first summer or two to help the plants get established, and make sure the weeds don’t outcompete any small plants. A year or two later you’ll have a low maintenance garden brimming with wildlife.
For a more in depth description of these steps, download the Rain Garden Handbook or talk to the Community Conservation Team, and invite them out to your property to help design your project.