Tip Sheet for Creating a Rain Garden
Critsite is an official supplier of native plants for Kansas City's "10,000 Rain Gardens" project.
Rain Gardens are a hot topic among avid gardeners. But what is a rain garden? Rain gardens are just another way of describing the long-used concept of a bioremediation swale, an area designed, excavated and planted to wildflowers and other native vegetation that soak up rain water, mainly from the roof of a house or other building.
A properly constructed and planted rain garden fills with a few inches of water after a rain and then, because of its ability to hold the water, will slowly filter the water into the ground rather than allow it to run off to a storm drain. Compared to a conventional patch of turf, a rain garden allows about 30% more water to soak into the ground.
So, why are rain gardens important and why should you consider adding one?
As cities and suburbs grow, our natural landscape is replaced with more hard surfaces and with landscapes that shed water faster than it can be absorbed. The increased stormwater runoff from developed areas increases flooding and also carries pollutants from streets, parking lots and even lawns into local streams and lakes. These results lead to costly municipal improvements in stormwater treatment structures. Conversely, if we reduce stormwater runoff through rain gardens and other effective measures, we can reverse these trends. An individual rain garden may seem like a small thing, but collectively they produce substantial neighborhood and community environmental benefits.
Rain gardens work for us to:
- increase the amount of water that filters into the ground to recharge local and regional aquifers;
- help protect communities from flooding and drainage problems;
- help protect streams and lakes from pollutants carried by urban stormwater;
- enhance the beauty of yards and neighborhoods;
- provide valuable habitat for birds, butterflies and many beneficial insects.
A few hints for choosing a spot:
Move away from the building. Locate your rain garden at least 10 feet away from your foundation to avoid foundation pressure, and build it on the down slope, if possible. Also, steer clear of the drain field of an existing septic system.
Call before you dig. Avoid excavating or planting near underground utilities and rights-of-way. Contact a local service like Dig-Rite and have the area flagged.
Be direct. You can install piping underground or send the rain along a constructed channel or swale to insure that your rain garden captures all the stormwater it can. You can also incorporate a rain barrel into the feature and save your rain water for other uses.
Protect your trees. Don't excavate an extensive rain garden under large trees. The excavation of shallow feeder roots can weaken or kill a tree. And if the tree is not a species that prefers moisture, the additional ground water may also damage it.
To calculate the most useful size of a smaller garden:
- Figure out what kind of soil you have.
- Estimate the area of hard surface from which your rain garden will get runoff. Include roof areas, driveways, and even areas of lawn.
- Determine the type soil you have to help establish the absorption rate. For sandy soil, your rain garden should be 20-30% of the drain area. For clay soil, your rain garden should be about 60% of the drain. Soils with a pH of 5.5 to 6.5 are best for the biochemical reactions that convert pollutants to harmless substances.
- If you improve your soil drainage and replace your soil with rain garden mix (50-60% sand, 20-30% topsoil, 20-30% compost), your rain garden should generally be about 20-30% of the square footage of your drain area.
- Mulching your new rain garden after planting with bark or wood chips or small gravel will help reduce weed invasion.
Rain gardens for single-family homes will typically range from 150 to 400 square feet. But remember, any rain garden is better than no rain garden. Even a small one will still be a great contribution to restoring clean water in your neighborhood, your city, and your region.
And also remember that good looks are important!
While rain gardens help protect water quality, they are also gardens and should be designed, constructed and maintained as an attractive part of your yard and neighborhood. Think of the rain garden in the context of your home and neighborhood's overall landscape design and style. This can be especially challenging when incorporating new-to-you native plants.
Here are a few tips for creating a beautiful rain garden:
Variety: Consider the height of each plant, bloom time and color, and its overall texture. Use plants that bloom at different times to create a long flowering season. Remember that rain gardens have higher and lower areas and therefore different moisture zones. The upper zone nearest the source of the runoff will be driest and can be planted with native shrubs, trees and perennials. The middle zone will be moist but may have dry times so choose plants that like moderate moisture like Rose Mallow, Cardinal Flower and Black-eyed Susan. The lowest part, or basin, of your rain garden will have the moistest soil and will occasionally be inundated. Choose plants that are naturally found on moist to wet soil such as Marsh Milkweed, sedges, rushes, and New England Aster. If the rain garden will have standing water for lengthy periods, you can add native plants like Blue Flag, Pickerel Weed and Arrowhead. Critsite's website "Plant Search" feature can help you select the right plants to give your garden depth and dimension through every season. Or consult the rain garden list found among "Plant Use List" under the site's "Native Plant" drop down menu.
Bold color: Randomly clump individual species in groups of 3 to 7 plants to provide splashes of color. Create repetition and cohesion by duplicating these patterns in the planting. More repetition and less species variety will produce a more formal appearance while increased diversity of species will create a more natural garden. Incorporate a diverse mixture of sedges, rushes, and grasses with your flowering species to develop necessary root competition and balance in your garden.
Make a statement: Enhance your rain garden by with local or existing stone, ornamental fences, trails, garden benches, or additional wildflower plantings. This will help give the new garden an intentional and cohesive look and provide a feeling of neatness that your neighbors will appreciate.