Rain Gardens: The silver BB

Photo courtesy of Justin Eibenholz

Photo courtesy of Justin Eibenholz

By Lisa Peterson-de la Cueva
TC Daily Planet
April 06, 2008

“Rain Gardens aren’t the silver bullet,” Rusty Schmidt said while playing with his daughter at the park. “But they’re the silver BB.” Schmidt, who planted fifty-six rain gardens last year, is a Natural Resource Specialist for Washington Conservation District. Bullet or BB, he was talking about long term solutions to storm water quality.

The old way of thinking about rain on our property went like this: Rain falls off your roof and onto your pavement or lawn, which we fertilize with chemicals. Some of the rain seeps into our garden while the rest of it flows into the street and down our storm sewers, which in turn dump the polluted water into rivers and lakes. It’s out of sight, out of mind.

Rain gardens negate the “out of sight, out of mind” rainwater mentality. A rain garden is basically a collection of Minnesota native plants with a depression, called a swale, in the middle of the garden. Instead of excess rainwater running into the street and picking up pollutants, the water seeps into the ground under the garden.

The thinking goes, if you use fertilizer or forget to fix that pesky oil leak from your car, that’s your choice. But then it stays in your yard and it’s your problem—or the next tenant’s.

Backyard rain garden captures run-off from roof and from impermeable surfaces. Photo courtesy of Justin Eibenholzl.

This brings up a knee-jerk reaction. Won’t all these contaminants just pollute your own property? Fair question. Native plants have particularly long roots, which help cleanse the rainwater as soaks into the soil. The gunk, like heavy metals and oils, stays on the top few inches of the garden. So yes, there will still be some long-term residue, but by the time the water gets through the roots it’s much cleaner than it would be with some other natural cleansing methods, like the use of pond algae.

This means that at some point down the line we’ll have to clean our own rain gardens. Rusty Schmidt said, “The theory is that in 50 years we’ll have to scrape off the top four inches of soil, put the plants back, and then let them do their thing again.”

Hence the BB, not the bullet.

Rain garden plants

Meg Arnosti and Rusty Schmidt listed their favorite rain garden plants. This list of their picks can help get you started with your own rain garden.

Flowering Perennials

Astilbe
Coneflower
Cranesbill Geranium
Daylily
Siberian Iris
Black-eyed Susan
Sunflower

Clay soil only
Blue Flag Iris
Blazing Stars
Sky Blue Aster
Spider Worts

Sandy soil only
Butterfly weed
Aromatic Aster
Rose or white turtlehead

Grasses

For the outer edges
Feather Reed Grass
Heavy Metal Switch Grass
Ice Dance Sedge
Hakonechloa
Soft Rush Grass

For the middle of garden

Carl Forester’s Grass
Fox, tussock, hop, or caterpillar sedge
Tall Feather Reed Grass

Clay soil only
Indian grass

Sandy soil only
Little Blue Stem
Prairie Dropseed
Blue or Side Oats Grama

Rain gardens work best in groups.

“You really need a whole bunch of them in a given location to do a lot of good,” Schmidt said. “If you had a city block with about half the houses with rain gardens, that would have an impact.”

A 2006 study of rain gardens in Burnsville showed promising results when rain gardens are planted en mass. The study by Barr Engineering Company compared the watershed runoff from residential homes in a concentrated area, one control group and the other with 17 rain gardens. On one day alone, with less than an inch of rainfall, the control group produced 35,107 gallons of runoff water. The homes with rain gardens, by contrast, produced only 994 gallons. The results show that if installed properly rain gardens “reduced the runoff volumes by approximately 90 percent.”

Schmidt says that Minneapolis is ahead of most cities in the nation, but it’s unclear just how the Twin Cities is doing. Metro Blooms, a non-profit that provides rain garden workshops, has documented over 450 rain gardens installed by its participants since 2005. The city of Maplewood, generally considered to be ahead of the curve on rain gardens, has planted at least 450. However, there is no centralized data to measure how many rain gardens have been planted in the metro area.

What’s in it for me?

Most people who install rain gardens are doing it because they have a stake in environmental issues. Joyce Vincent, Board Chair of Metro Blooms, said, “It’s about participants’ awareness and caring about the environment, not necessarily about their income level.” Vincent did admit, however, that it takes a certain amount of financial stability to install a rain garden.

Getting people think green about their lawns, and getting them to actually implement rain gardens is a different story. There are currently few monetary incentives for individuals to install rain gardens.

The city of Minneapolis has been promoting the Metro Blooms program, which has had over 2,500 participants in their rain garden workshops since their program began in 2005. The city also offers a stormwater credit to residents and businesses that install rain gardens. The credit helps residents a few dollars a month on their water bill. The pay off can be higher for businesses that install large-scale rain gardens and water management infrastructure.

Karl Westermeyer, a Stormwater Utility Administrator at the City of Minneapolis said, “The program is as an educational and motivational tool, but in reality it’s not a big financial incentive.” Getting people interested in rain gardens is the first step, Westermeyer said, and a small financial incentive is the hook. It’s turns out it’s not hooking too many people, though; the city has processed under 200 commercial and residential applications since the program began in August of 2005.

The plan—install a rain garden and pay less on your water bill—fell through with Justin Eibenholzl, who installed four rain gardens in his Southwest Minneapolis home. Eibenholz got into squabble with the city when his bill actually went up by 60 dollars a year. The city had never actually measured his plot, so after Eibenholz sent in his application for the stormwater credit the city found out he should have been paying more in the first place.

Eibenholz’s case is atypical and most people do save a little money. But Eibenholz also has a professional interest in rain gardens; he works for the Southeast Como Improvement Association in Minneapolis and is trying to promote their use in Como. “We have to reevaluate what we’re doing here in Como,” Eibenholz said. “We were going to go out and promote the financial incentive, but if there’s not really one then we have to think of something else.”

Besides keeping our scum out of rivers and lakes, that is.

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