What is a Rain Garden?
A rain garden captures runoff from your rooftop before it reaches the storm drain network. A rain garden uses native landscaping to soak up rain water directed from your downspout. The middle part of the garden holds several inches of water, allowing it to slowly infiltrate into the ground instead of being delivered to the storm drain all at once.
Why Install a Rain Garden?
A rain garden allows 30% more water to infiltrate into the ground than a conventional lawn. This helps replenish the groundwater supply (important during a drought!), and reduces the amount of pollution that reaches our streams through stormwater runoff. Since studies show that the first inch of rainfall is responsible for the bulk of the pollutants in stormwater, a rain garden is designed to temporarily hold water from a one-inch rainstorm, and slowly filter out many common pollutants like sediment, oil, grease and nutrients. Rain gardens require less watering and fertilizer than conventional lawns, and can provide habitat for bird and butterflies.
Rain Garden Supplies
Can be found at most hardware stores
Rope of string
Shovel or spade
Downspout extension (optional)
Humus or other planting medium (optional)
Instructions: Follow the four steps to install a rain garden in your yard.
Step 1: Size the Rain Garden
Measure the footprint of your house and determine how much of the rooftop area drains to the downspout you will be direction to your rain garden (for gutters with a downspout at each end, assume that half the water goes to each downspout).
Be sure to measure the house footprint only; do not take the roof slope into account. The surface area of your garden should be between 20% and 30% of the roof area that will drain into the rain garden (use 20% for very sandy soils). Locate the garden at least 10 feet away from the house (to prevent soggy basements), and maintain a minimum 1% slope from the lawn down to the rain garden. You can also create a shallow ditch to ensure the water flows from roof to the garden, or use a downspout extension to direct the flow into the garden.
Rain garden sizing example:
30’ x 30’ house area
¼ of this area drains to one downspout
15’ x 15’ = 225 ft2
20% of 225 ft2 = 45 ft2
30% of 225 ft2 = 67.5 ft2
Rain garden area = 45 ft2 to 67.5 ft2 for a 1-inch storm
Step 2 Locate the Rain Garden
Using a measure tape and rope or string, lay out the boundary of the rain garden
Step 3: Dig the Rain Garden
To enable the rain garden to hold several inches of water during a storm, the surface of your rain gardens will have to be 3-4 inches below the surface of your yard. You will have to dig a hole 3-4 inches deep across the entire surface of the garden before planting. If the soil in your yard is not suitable for planting, you can improve it by digging the hold 5-6 inches deep, and adding 2-3 inches of humus or other organic planting material.
Make sure the bottom of the garden is level. Test how the garden will hold water during a storm by letting water flow into the rain garden from a hose placed at the downspout. Based on this test, make any necessary adjustments (e.g., create a berm on the lower side of the garden using the diggings, or use a downspout extension or shallow ditch to direct the water into the garden).
Step 4: Add Plants to the Rain Garden
Choose drought-tolerant plants that will not require much watering, but make sure they can withstand wet soils for up to 24 hours. A list of native plants that meet these criteria is provided below. Also take into account how much sun your garden receives.
It’s often helpful to draw out a planting plan before your start, and mark planting areas within the garden with string. After planting, weeding may be required until the plants become more established. You may also need to periodically prune some of the plants to let others grow. In the winter, leave dead or dormant plants standing and cut back in the spring. Your garden may need a bit more maintenance than a lawn in the beginning, but in the long run it will be easier to care for and provide many added benefits!
Native Plants for Rain Gardens
Canada wild rye
Bottle brush grass
Part sun/Part shade
Blue wood sedge
New England aster
Yellow flag iris
St. John’s wort
Fern – rattlesnake fern
Rain Gardens: A household way to improve water quality in your community University of Wisconsin – Extension and Wisconsin Department of Natural Resources
University of Connecticut – Extension and Natural Resources