It happens every time a heavy downpour occurs – rainwater flows out of your home’s downspouts, sending streams of water across your lawn and driveway, where it collects fertilizer, dirt, debris, and chemicals, and then runs into the storm drain.

Storm water runoff is a huge source of water pollution, so preventing as much of it from reaching the storm drain is encouraged.

There’s a perfect way to lessen storm water runoff, one that adds both beauty and a strong dose of environmental sensitivity to your yard — creating a rain garden.

Rain gardens are landscaping features that are specifically designed to catch water from gutters, filtering out pollutants and allowing it to absorb into the ground instead of running into the street.

rain-garden-diagram

Here are a few key tips on how to build a rain garden:

  • Rain gardens should be located at least 10 feet from any structure, so as not to damage building foundations, and should also not be located above utility lines.
  • The water table should not be too high – test this by digging a hole between six and eight inches deep, then filling it with water. The water should fully drain within 12 hours. If it doesn’t, look for another location.
  • Determine how big and how deep your garden needs to be. This will be determined in part by how much water will be deposited and the type of soil.
  • Dig the garden to its desired depth and make sure the bottom of the basin is level. The basin should be anywhere from three inches to two feet deep, depending on the topography of the area.
  • Build a berm on the downhill edge of the basin to prevent water from pouring out of the garden during heavy downpours.
  • Choosing the right flora for the garden is especially important – pick plants that are tolerant of large quantities of water, and those with strong root systems that can readily absorb moisture.
  • Add a layer of mulch around the plants to further absorb rainwater, prevent overflows, and keep weeds from growing.

If properly cared for during the first two years or so, your rain garden should eventually require little maintenance, and will serve as a lovely and useful addition to your yard!

For more information on backyard conservation practices, including a section on rain gardens, please check out the Hawaii Backyard Conservation booklet.