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How and why to build a rain garden

Quick facts

A rain garden is a planted low area that allows rainwater runoff from hard surfaces (like roofs, driveways, walkways and parking lots) to soak in.

Rain gardens:

  • Remove pollutants from water before it enters surface waters.
  • Prevent erosion by holding soil in place with their deep roots.
  • Attract birds and butterflies.
  • Require little watering and maintenance once established.

The benefits of rain gardens

Whether you live in the city or along a lake or river, managing stormwater runoff is important.

Rooftops, roads, driveways and sidewalks are hard surfaces that prevent rainwater and melting snow from reaching the soil and soaking into the ground. These hard surfaces also collect nutrient-rich yard and pet waste, oil and radiator fluid from autos, and other debris and pollutants.

Runoff:

  • Washes debris and pollutants away, often directly into lakes, rivers and wetlands.
  • Erodes soil and carries it into our surface waters.
  • Can affect aquatic life if warm runoff enters lakes and rivers directly. In summer, runoff is often warmed as it flows over hard surfaces. 

Rain gardens:

  • Collect stormwater runoff and prevent it from flowing directly into lakes, rivers and wetlands.
  • Allow runoff to soak into the soil so sediments settle and plants absorb nutrients.
  • Filter out pollutants from water before entering the groundwater.
  • Prevent erosion by holding soil in place with their deep roots.
  • Attract birds and butterflies.
  • Require little watering and maintenance once established.

Design and placement

Rain garden designs can be simple or elaborate, depending on your gardening interest and experience. Before you start digging, it's best to sketch a design. You'll need to consider:

  • Location of the garden. 
  • Size you need.
  • Shape you want.
  • Type of soil you have.
  • Plants you’d like to include.
  • How much runoff you typically have.
    • You may need more than one rain garden to accommodate the runoff.
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Building and planting

Construction can begin once garden size, shape, location and plants have been decided.

  • Lay out a rope or hose in the desired shape to use as a guide for digging.
  • The depth may vary from 4 to 10 inches.
  • For best infiltration, the bottom of the rain garden should be level.
  • If your garden is placed on a slope, use the soil from digging to create a berm on the downhill side of the rain garden.
  • Remove excess soil from the site.

Reviewed in 2018

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