When it rains, it pours. How can a rain garden help?
We've spoken about rain gardens many times over the years but people always have questions about what their primary function is and how much they cost. Now that rainy season is approaching, it's a good time for a refresher course!
What is a rain garden exactly? It's a depression designed to temporarily store rainwater runoff from impervious surfaces like roofs, driveways and walkways. A rain garden is normally lower than the surrounding ground level and the bottom layer is usually filled with stone, to allow runoff to collect within it. During a rainstorm, they catch water, filter it and then allow it to slowly absorb into the ground. This approach improves the quality of the water and takes pressure off of nearby waterways where excess rainwater is directed. Our rain gardens use native perennials, grasses and shrubs that love the change from dry to oversaturated conditions.
Before we talk about cost, let's talk about the benefits of having a rain garden. Though there are lots of good reasons to put one in your yard, the number one thing rain gardens are designed to do is manage stormwater. With the right placement in a yard and with the right design, a rain garden can turn a soggy backyard into a paradise or transform a boring spot into a eco-wonderland. Rain gardens are a form of green infrastructure, and are ideal for residential homes. They couple beautifully with other green infrastructure techniques (i.e. green roofs, rain water harvesting, bioswales, etc.) to make your rainwater work best for your space. Additionally, rain gardens create micro-habitats, improve the health of pollinators, look incredible, naturally fight mosquitoes, and the list goes on.
Image from the Philadelphia Water Department Website.
We love to use flowers such as Lobelia cardinalis, Iris versicolor and Juncus effusus at the lowest points because they both do very well in super moist spots. Places that are less saturated would have plants like Liatris spicata, Mountain mint, coneflowers, aster, bee balm, etc. Rain gardens look best when there’s a base of grasses that act as a sea of green and then have flowers installed in clumps or as individuals to add seasonal color.
If you build the rain garden correctly, you can manage nearly all of the rainwater coming off your roof or driveway. This means hundreds, if not thousands, of gallons of runoff will be dealt with in a more natural way and you'll be doing your part to help the environment.
Of course, rain gardens do need to be maintained. Weeding and plant replacement will be a yearly activity, and for the first two years, you may need to use sprinklers to get the plants to root. The work is worth the benefit though. You’ll be amazed as the garden matures. You might even forget that it’s a piece of infrastructure, because you’re too busy admiring its beauty.
The costs associated with a rain garden installation are generally slightly higher than those of installing a typical landscaping treatment. The increased costs are due to the increased number of plantings, the need for additional soil excavation and backfill material and the use of underdrains in some cases.
The cost of a rain garden can vary and is based on several factors including:
The area of the rain garden
The depth of the rain garden
Plant choice
Whether or not the soils on site can be reused, etc.
The typical range for a professionally installed rain garden is about $30-45 per square foot.