Rain gardens 101

  • Article by: LYNN UNDERWOOD
  • August 26, 2009 - 7:47 AM

Rain gardens are taking root among eco-conscious gardeners. By planting a garden that captures rainwater runoff, you can help improve the water quality of lakes and streams, and in the Twin Cities, the almighty Mississippi River.

"A rain garden is the latest `think globally, act locally' way to have clean water," said Lorrie Stromme, a University of Minnesota Extension horticulturist. "Even a rain garden as small as a queen-size blanket can help."

Rain gardens large and small do more than benefit the Earth: the plants can be prolific bloomers as well as butterfly magnets. Plus, the mix of deep-rooted, hardy wildflowers and prairie plants, many native to Minnesota, don't need much TLC once established.

"People are looking for a way they can help the environment and have something that is attractive for them and for birds and butterflies," said Roy Robison, owner of Landscape Alternatives, a native plant nursery in Shafer, Minn.

And all you need is a shovel and a patch of earth.


A rain garden is a shallow depression (natural or manmade) into which runoff from roofs, driveways, sidewalks and lawns is routed. Rain gardens are usually planted with native species that capture and filter water, reducing the pollution that enters storm sewers and, eventually, lakes and streams.


Choose a location: Make sure it's at least 10 feet from the foundation of your home. If possible, place the garden near downspouts and surfaces that produce runoff, such as alleys, sidewalks and driveways, or choose an existing low area in your yard. Before you dig, locate underground utility lines.

Test the soil for drainage: Dig a hole about 1 foot by 1 foot and pour water into it. Observe how long it takes to soak in and drain away. The most promising sites drain within 24 hours. If the soil doesn't drain well, dig deeper and till in compost and topsoil, then perform the test again. Clay should not exceed 10 percent of soil composition.

Dig in: Dig the garden 4 to 8 inches deep in a bowl shape with a flat bottom. The sides of the garden should gently slope up toward the lawn.

Plant picks: Select a mix of deep-rooted perennials that can tolerate extreme dry and wet conditions. Many of the prairie plants and wildflowers native to Minnesota will work. Place moisture-loving plants in the center and those that favor dry conditions along the edges of your garden. Spread a layer of shredded wood mulch around the plants.

Care: Make sure plants get at least 1 inch of water each week for the first three months. Once they are established, most rain gardens are low-maintenance. However, like all gardens, they need routine weeding, pruning, watering and mulching.



One of the more elegant rain garden plants, this moisture-loving iris, right, features striking violet-blue flowers from May into June. Although the exotic-looking blossoms are short-lived, its lush foliage lasts all season.

Plant: In the moist center of the garden.

Size: 2 to 3 feet tall.

Best in: Full sun to part shade.


This taller, bushier cousin of the common black-eyed Susan, above, is a long-lived wildflower that boasts fragrant lemon-hued flowers in late summer .

Plant: On the garden's edge.

Size: 3 to 5 feet tall.

Best in: Full sun to partial shade.


This crowd-pleaser produces masses of purple and pink flowers that bloom around State Fair time and encourage visits from bees and butterflies. The sturdy, erect stems won't flop.

Plant: Edge or center.

Size: 3 to 5 feet tall.

Best in: Full sun to light shade.


A must-have if you want butterflies in your rain garden. It's a food source and host plant for monarch butterflies. The rose-pink flowers bloom from June to August, then create attractive seed heads.

Plant: In the center.

Size: 2 to 4 feet tall.

Best in: Full sun.


Butterflies and hummingbirds flit around the dense spikes of showy lavender flowers. These late-summer bloomers look as good in the garden as they do in a vase.

Plant: On the edge.

Size: 2 to 4 feet tall.

Best in: Full sun.


This upright, clump-forming prairie grass morphs into a blazing orange -red in the fall. It also provides cover and feeding sites for ground-nesting birds.

Plant: On the edge.

Size: 1 to 3 feet tall.

Best in: Full sun to partial shade.


Popular with hummingbirds, this flower is named for its scarlet spires that bloom in mid- to late summer. Only a handful of native perennials bear red flowers. The plant is short-lived, lasting only about four years.

Plant: Edge or center.

Size: 2 to 3 feet tall.

Best in: Full sun to partial shade.

Sources: Roy Robison, owner of Landscape Alternatives; Lorrie Stromme, University of Minnesota Extension horticulturist; Sherri Buss, landscape architect at Bonestroo and Associates, who designed the city of Maplewood rain garden plans; Douglas Owens-Pike, owner of Energyscapes.

This story originally ran May, 17, 2006

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