Creating a Rain Garden: How to Get Started and Maintenance Tips

A rain garden is an easy way to save water, stop runoff, and support wildlife.

Rain Gardens at Arlington National Cemetery
Rain Gardens at Arlington National Cemetery.

Arlington National Cemetery / Flickr / Public Domain

Overview
  • Total Time: 4 - 8 hours
  • Skill Level: Beginner
  • Estimated Cost: $3-5 per sq. ft

A rain garden is merely a garden in a low-lying patch of land. If you have a place in your yard where water collects after a rainstorm, you have the perfect spot for a rain garden. Building one takes more time than a traditional garden, but the payoff is that it is nearly maintenance free.

Benefits of a Rain Garden

A low point in a yard where rain collects.
A great candidate for a rain garden.

Puripatch Lokakalin/Getty Images

Sediments, pollutants, and other debris accumulate on surfaces during dry periods and run off during the first rain after a dry spell, especially during the first inch of rain. When placed near roadways or other impermeable surfaces, rain gardens act as filters of those materials, slowing down the dispersal of sediments so that water treatment facilities aren't overwhelmed. That runoff is absorbed into your rain garden's soil, where microbes can break it down. The filtration provided by your rain garden means your groundwater is naturally replenished with clean water. Gravity-driven filtration has a zero carbon footprint, unlike the energy that water treatment plants require.

Rain gardens capture 30-40% more runoff than traditional lawns, according to the U.S. Department of Agriculture. Compared to a single-species lawn, a rain garden's wider variety of plants can provide a healthier home as plants die and create food for the many creatures living in the soil. And with increasing weather disturbances due to climate change, a rain garden is more likely to survive swings between drought and deluges.

What You'll Need

Tools

  • 1 tape measure
  • 1 to 2 shovels
  • 1 to 2 rakes
  • 1 to 2 trowels
  • 1 ball twine or string
  • 2 wood stakes, 3 inches long
  • 1 carpenter's level
  • 1 mallet or hammer

Materials

  • 2 inches of compost per square yard
  • 2 to 4 inches of loam soil per square yard (optional)
  • mix of plants

Instructions

Placement Tips

  • Don't put a rain garden over a septic system.
  • A rain garden set back at least 10 feet from your home can prevent water from flowing into the basement.
  • Consider placing your rain garden in the front of your house. Curb appeal increases the resale value of your house.
  • Determine the lowest-lying area of your property during a heavy rain. Either create your rain garden there, or slope your land from that lowest spot down to your rain garden.
  • Dig safe. Contact your local utility companies to make sure you avoid underground utility lines.
  • Rain gardens work best in full or at least partial sun.
Rain garden

Field Outdoor Spaces / Flickr / CC BY 2.0

Prep Steps: Soil, Size, and Slope

Here is the prep work needed before you build your rain garden. There's a little math and measuring involved, but nothing too complicated.

  1. Determine Drainage

    Determine the drainage area from which runoff will drain into your rain garden. Include any portions of a roof that will drain into your rain garden. Multiply width by depth to determine square footage.

  2. Measure Your Slope

    Measure the slope of your drainage area to see if you have a good site for a rain garden. You can use the old-fashioned method of stakes, string, and a level, or (if your slope is relatively constant) use a phone app like iHandy. The steeper your slope, the deeper your rain garden's lowest point should be.

    For example, a slope of less than 4% will require a garden depth of 3 to 5 inches, while a 10% slope will require one of 8 inches.

  3. Determine Depth

    Test the drainage of your soil to determine how deep the lowest point of your rain garden should be. Dig a hole about 6 inches deep at the lowest point of your proposed rain garden. Fill the hole with water, then mark where the water line is.

    After four hours, mark the water line is again and measure the distance between the two marks. Multiply that distance by six to determine the maximum depth of your rain garden. Your rain garden should be able to drain completely in 24 hours, so, for example, if the distance between the two marks is one inch, your garden will drain 6 inches in 24 hours. Your lowest point should be no more than that.

    Soil Types

    Loam soil, a mix of sand, silt, and clay, is the ideal mixture for growing most plants because it drains easily yet retains the nutrients and microorganisms that make for healthy soil. Sandy soil and loam soil drain quickly, while clay soil drains poorly and plants take longer to establish themselves.

  4. Check Your Measurements

    A typical rain garden is between 4 and 8 inches deep. If there's a mismatch between the slope of the drainage area in step 2 and the drainage rate of your rain garden in step 3, you may need to expand or contract the size of your rain garden, or you may not have an ideal spot for a rain garden at all. A quickly draining rain garden with a low sloping drainage area may end up just being a garden, while a slow-draining rain garden with a steep drainage area may be better off as a water garden.

    Ideally, a rain garden with well-draining soil should be no more than 30% of the total drainage area, while a rain garden with slower-draining clay soil can be up to 60% of the total drainage area. (You can also amend clay soil with compost and sand to improve drainage.)

Building Your Rain Garden

While the drainage area should slope toward the rain garden, the rain garden itself should be level so that water is distributed evenly throughout it. Get some friends to help digging, and the job is completed quickly.

  1. Outline the Garden

    Use string to outline your rain garden.

  2. Kill the Grass

    Kill the grass. Cover it with a black plastic until the grass dies.

  3. Start Digging

    Dig your rain garden an inch deeper than the desired depth, making sure that the depth is consistent throughout the garden.

  4. Add Compost

    Add 2 inches of compost and turn it into the soil with a garden fork. Water it in. It will settle into your desired depth.

  5. Build a Berm

    Build up a well-compacted berm along the outer edge of the rain garden to keep water in the garden. Add stones or other decorative materials along the berm.

  6. Back-Fill With Soil

    Back-fill the rain garden with the soil you removed or (preferably) add new loam soil to the desired depth.

    Optional: Lay down a weed block over the entirety of your rain garden, creating holes where your plants will go.

  7. Add Plants

    Plant your plants, arranged by height, starting from the center. Larger plants require more water, so place them in the middle of a rain garden. Plant deep-rooted plants that can take advantage of the moisture at lower levels of the soil. Place shorter plants along the border of the garden, so that they are visible and also have the opportunity to capture runoff before it makes its way to the lowest points of your rain garden.

    The Right Plants in the Right Place

    Native plants that will work in a traditional garden will also work in a rain garden. Choosing the right plants for the right place depends on how much sun your rain garden gets, how quickly the soil drains, and the climate in your region. The only difference is that your plants will need to be able to withstand variations in water levels. Check with your local greenhouse for suggestions.

  8. Add More Compost

    Top-dress your plants with a compost/mulch to retain soil moisture.

  9. Water

    Water immediately after planting, then one inch of water per week until they are established.

Maintenance

During the first year, watering and weeding are important. But once established after a year, a properly designed rain garden is self-watering, and when using native plants, can be self-maintaining, needing no fertilizers. The only maintenance will be an annual top-dressing of compost and some pruning of dead vegetation or of plants that have outgrown their space. A healthy garden is the best weed prevention, as healthy native species out-compete intruding weeds.

Frequently Asked Questions
  • What's the difference between a bioswale and a rain garden?

    Whereas bioswales are designed to catch rainwater and move it to different parts of a garden, a simple rain garden allows the water to infiltrate the soil beneath it. Sometimes bioswales are used to move water to a rain garden.

  • What are some plants that absorb a lot of water?

    Ferns, daylilies, Indian grass, cattails, and irises thrive in marshy conditions.

  • Don't rain gardens attract mosquitoes?

    Rain gardens don't attract mosquitoes because the water doesn't stand for more than 24 hours. Mosquitos need at least seven days to lay and hatch eggs. In fact, rain gardens do attract dragonflies, which happen to feed on mosquitoes, so you're more likely not to have a mosquito problem with one of these in your yard.

  • How do you determine how deep your rain garden should be?

    If the slope leading to your rain garden is less than 4%, you should aim for a depth of three to five inches; between 5% and 7%, six to seven inches; and 8% to 12%, eight inches. If the land slopes more than 12%, a rain garden is not advisable.

  • How clean do rain gardens get the water?

    The Groundwater Foundation says a rain garden can remove 90% of chemicals and 80% of sediments from runoff.

View Article Sources
  1. "What Is a Rain Garden?" United States Department of Agriculture.

  2. "Rain Gardens: A How-To Manual For Homeowners." Wisconsin Department of Natural Resources.

  3. "All About Rain Gardens." Groundwater Foundation.