A rain garden is a shallow depression that is planted with deep-rooted native plants and grasses. Rain gardens are designed to absorb runoff from impervious surfaces such as roofs and driveways. They are an attractive and effective way to reduce flooding, recharge groundwater, and improve water quality.
Building a rain garden is a great weekend project that the whole family can help with. Here are some easy steps to get you started.
1. Select a location for your rain garden
A rain garden should be located at least 10 feet away from your home or other buildings. It should also be located in an area where runoff from rainfall can drain naturally. Avoid low spots where water would pond, and avoid areas where drainage already exists.
The size of your rain garden will depend on the amount of runoff from rainfall and the available space in your yard. A good rule of thumb is to make your rain garden about 30% the size of the impervious surface that drains into it. For example, if you have 1,000 square feet of roof area, your rain garden should be about 300 square feet in size.
2. Clear the area of debris and grass
Once you have selected a location for your rain garden, use a shovel to clear the area of debris such as rocks and sticks. Next, use a spade or sod cutter to remove the grass from the area. Be sure to stockpile the sod so that you can use it to patch any bare spots in your lawn after you have finished building your rain garden.
3. Dig a shallow depression
Use a shovel or spade to dig a depression that is 6 to 12 inches deep in the center and slopes gently outward towards the edges. The sides of the depression should have a slope of no more than 3:1 (three inches horizontal for every one inch vertical). This will ensure that rainfall does not erode the sides of your rain garden.
The depressed area should hold water for at least 24 hours after a heavy rainfall but drain within 48 hours so that mosquito breeding is avoided. If necessary, amend the soil with organic matter such as compost or peat moss to improve its infiltration rate.
4. Choose plants for your rain garden
Rain gardens are typically planted with deep-rooted native plants and grasses that can tolerate both wet and dry conditions. Some good choices include: blue flag iris, buttonbush, cardinal flower, cattail, sedges, swamp milkweed, wood aster, and yellow loosestrife.
Be sure to select plants that are appropriate for the amount of sun or shade present in your chosen location as well as for the soil type (sandy, loamy, or clay). Most native plants can be purchased from local nurseries or online retailers specializing in native plants.
5. Install plants and mulch
After planting, spread 2 to 3 inches of organic mulch over the soil surface to help suppress weeds and maintain moisture levels during dry periods. Be sure not to pile mulch up against plant stems as this can cause rot problems.
Water your new rain garden deeply once per week during its first growing season Thereafter, supplemental watering will only be necessary during prolonged periods without rainfall (4 weeks or more).
Rain gardens are attractive features that serve an important function in the landscape by reducing flooding, recharging groundwater aquifers, and improving water quality by filtering pollutants from stormwater runoff before it enters our lakes and streams.