What’s a Rain Garden and How to Build One
A rain garden gathers water runoff and allows it to seep into the ground. Being filled with water-loving plants, it can also be a beautiful addition to any landscape.
Why Build a Rain Garden?
There’s a new kind of garden in town. It’s easy to establish, looks good year-round, and has a positive impact on the environment. It’s called a rain garden.
A rain garden is a unique kind of garden, designed to gather stormwater runoff from a roof, driveway, or other impermeable surfaces. Instead of running off into a storm sewer or waterway, the rainwater gathers in a shallow depression on your property.
This area is planted with native grasses and wildflowers that are carefully selected for their ability to steadily absorb and filter stormwater. Rain gardens can also have a major impact on the water quality in our communities. Studies have shown that up to 70% of the pollution in streams, rivers, and lakes has been transferred there by stormwater.
By taking responsibility for the rainwater that falls on our roofs and driveways, we can help protect our rivers, streams, and lakes from runoff and potential pollution. The addition of a rain garden to your yard will also provide habitat and food for wildlife while giving you a new garden that’s hardy, low maintenance, and naturally beautiful!
Check out the Virginia Department of Forestry’s book, Rain Gardens Technical Guide – A Landscape Tool to Improve Water Quality, for a comprehensive guide to establishing your very own rain garden:
What You’ll Need
Equipment / Tools
- Tree/shrub trimming tools
- Cover pump or submersible pump (as needed)
- Broom or pressure washer (as needed)
- Cover removal took or Allen wrench )as needed)
- Tile brush
- Pool brush
- Pool vacuum
- Pool water testing kit
- Tile cleaner or baking soda
- Metal lubricant
Choose the Site
It is important to place your rain garden at least 10 feet away from your home. Low spots in your yard that often collect water after a heavy rain are natural sites to install a new rain garden. Ideally, this area receives full sun, if this not, the area should receive at least a half-day of sunlight. A natural slope (1 percent grade minimum) leading from the water collection area (your roof or driveway) to the rain garden. Choosing a reasonably level spot for the garden will keep digging to a minimum.
Prepare the Soil
Once identifying your new garden’s location, begin removing the sod, and dig a shallow depression roughly 6″ deep. Gradually slope the sides from the outside edge to the deepest area. Build up a raised area on the lowest side of the garden using the soil that you removed. This berm will help hold stormwater and allow it to slowly percolate throughout the rain garden.
If your rain garden isn’t more than 6″ deep, stormwater will often be absorbed within a one to seven-day period. This will help you avoid mosquitoes as they require seven to 10 days to lay and hatch their eggs. You can also make one part of your rain garden deeper, such as 18 inches in the deepest spot if you want to create an area with standing water for fish and amphibians. Lining this area of the garden with plastic to help retain a small pool of water may be necessary depending on the type of soil that you have (sand, clay, loam).
Typically a residential rain garden is 100 to 300 square feet, but any size rain garden is fine. You can also calculate the best size for a rain garden, based upon the surface area of your roof, soil type, and the distance from your home in which the garden resides.
Downspouts from your roof or the sump pump outlet from your basement should be pointed toward your rain garden depression. This can be achieved by a natural slope, digging a shallow swale, or redirecting the runoff directly to the garden through a buried 4″ diameter plastic drain tile.
Choose Native Plants
Withstanding difficult growing conditions and requiring little care, native plants are always the best choice for rain gardens. When selecting the plants, keep in mind their height, bloom time, and color. Clumps of three to seven plants of the same variety will look better than lots of singles.
Mix native ornamental grasses and sedges in with your perennial wildflowers to make sure that the garden has a strong root mass that will counter-act erosion while inhibiting weed growth. New plants should be watered approximately every other day for the first two weeks. Once established, your garden should flourish without additional watering. Fertilizers should not be necessary, and only minimal weeding will be needed after the first summer of growth.