Rain Gardens

Rain gardens are in bloom
A rain garden is a shallow, constructed depression to catch rainwater. It contains plants that tolerate standing water for several hours. If it is designed properly, all water from a rain event will drain out of the garden within 48 hours.

Rain gardens receive a rush of polluted stormwater from hard surfaces (such as sidewalks, driveways, roofs, and streets), hold the water for a short period of time, and allow it to naturally infiltrate into the ground to remove pollutants and recharge groundwater rather than running off into a storm drain. Compared to a patch of lawn grass, a rain garden allows about 30% more water to soak into the ground. (Rain Garden Network Spring 2009 newsletter, v 4.2)

Why are rain gardens important?
As cities and suburbs are developed and replace forests and agricultural land with impervious surfaces, increased stormwater runoff becomes a problem. Stormwater runoff from developed areas increases flooding; and carries pollutants from streets, parking lots and even lawns into local streams and lakes. While an individual rain garden may seem like a small thing, collectively they can produce cumulative water quality benefits.

How do rain gardens help?
Rain gardens increase the amount of water that filters into the ground, removing pollutants and recharging groundwater. This helps protect lakes and rivers by intercepting urban stormwater that would have run off hard surfaces and picked up pollutants along the way. These pollutants include lawn fertilizers, leaves and grass, sediment, pesticides, oil and other automotive fluids, and bacteria from pet and wildlife waste. Rain gardens also enhance the beauty of yards and neighborhoods and provide valuable habitat for birds, butterflies and many beneficial insects.

Here are a few things you’ll need to consider when building a rain garden:

  1. Location
    A rain garden should be located at least 10 feet away from building foundations and near a spot where the raingarden will receive direct rainwater, such as near gutter downspouts. Try to locate the garden in either sun or partial sun.
    If you have pooling or erosion gullies on your property, position your garden to intercept water before it gets to these non-infiltrating spots.
    Look for a location where a flower bed will fit and allows for shallow digging, and consider where water will flow overflow from the rain garden. Make sure this overflow water is not directed at your house, as this may contribute to a wet basement.
  2. Size
    When determining the size of your garden you’ll typically measure the specific drainage area (in many cases, a portion of the rooftop) and multiply by the number associated with the type of soil you have: for sandy soil multiply by 20%, for loam use 35% and for clay use 60%. These numbers are somewhat inflated but they will ensure the garden holds as much water as possible. CRWD can help with these calculations as part of the Stewardship Grant application process.
  3. Design
    Plan your garden on paper first. The outer edge of the rain garden can be dug in a shape that fits the site and type of plants you’ll be using – you’re not limited to a rectangle. There is a host of plants – Minnesota native plants, shrubs, and garden perennials – that will perform well in your rain garden. See resources below for ideas

        

  4. Safety
    In Minnesota, call GOPHER ONE CALL before digging to avoid placing your garden over buried utilities. Avoid placing your rain garden in the boulevard (the area between the street and the sidewalk) since gardens won’t typically receive enough water in this spot. These areas also often contain multiple buried utilities. Also avoid placement under trees since digging may damage tree roots; over areas of shallow bedrock; and behind retaining walls not structurally designed for drainage.

What’s next?
If you live in the Capitol Region Watershed District, you may qualify for a cost-share grant to help design and fund your rain garden project. Visit our Grants page for details.

For do-it-yourselfers, there are many resources available if you decide to create a rain garden yourself. Applicants to CRWD’s Stewardship Grant Program can receive a free visit from a technician to help site the garden, determine soil type, and create a planting plan.

Other resources include:

The Blue Thumb Partners – a collaborative group of stormwater educators who advocate for native planting to protect water quality.
www.bluethumb.org

Rain Garden Network – rain garden education and consulting group. Free newsletter with year-round maintenance tips
www.raingardennetwork.com/

City of Maplewood, MN Stormwater Management – Design tips and planting plans from a city with more than 450 residential raingardens
www.ci.maplewood.mn.us/index.aspx?nid=456

If you’d like to hire a professional to do the work for you, Blue Thumb Partners website lists landscape and natural resource professionals who have been trained in rain garden design: www.bluethumb.org. Portions of costs paid to a landscape professional are typically considered an applicant’s project share when applying for a CRWD Stewardship Grant.