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Plant a rain garden to keep the rivers clean

by: PHOTO COURTESY OF OREGON DEPARTMENT OF FORESTRY  - Bleeding heart is a fine choice for a rain garden. Anyone who has lived through a few winters in the Pacific Northwest is familiar with the after-effects of significant rainfall. Roads get slick, streets can become flooded and clogged drains and roof gutters can become a nuisance.

What many don't stop to realize is that the rain or melting snow that runs off our roofs, driveways and lawns is untreated, and carries with it pollutants like fertilizer, pet waste, pesticides and oil. The cumulative effect of you and your neighbors’ pollutants moving untreated into local rivers is a scary thought, indeed.

In a natural forested landscape there’s not much storm water runoff, because most rainwater filters down through soil or evaporates back into the atmosphere. Paved surfaces and even seemingly porous areas like lawns (and their pesticides, fertilizers, and pet waste) in our cities and towns create a different scenario.

How can we help re-create the natural water cycle and reduce water quality problems? One way is by planting a rain garden. A rain garden is a shallow depression planted with deep-rooted native plants and grasses that can capture the urban runoff from rooftops and paved surfaces and prevent it from entering the community's water system.

The quantity of pollutants coming from your household can easily be handled by a rain garden. During a storm or shower, your rain garden will soak up water runoff from the roof, driveway and other paved surfaces, and that water slowly seeps into the ground instead of heading for the nearest storm drain. In short, rain gardens are a simple way to make a difference.

Most rain gardens percolate incoming water through a series of soil or gravel layers, and are usually located near a gutter downspout or a swale that can direct runoff to the rain garden.  Plants selected should tolerate both dry and saturated soil, so using native plants is highly recommended. Not only will your garden require less maintenance, it also will contribute to urban habitat for local butterflies, birds and beneficial insects.

by: PHOTO COURTESY OF OREGON DEPARTMENT OF FORESTRY - Yarrow makes a good addition to a rain garden. What to avoid

"One of the biggest mistakes people make is trying to get a ‘rocky creek bed’ look," says Maria Cahill, sustainable site specialist with Green Girl Land Development Solutions. “Not only is this hard to maintain, the runoff doesn't really get treated this way, either," Cahill says.

Another problem, she says, is that "a lot of parts of the Portland area have slower draining clay soils. In Portland communities your rain garden might fill up pretty fast, so make sure water has someplace to overflow."

An overflow structure allows water to exit your rain garden. A grass-lined swale or area of lawn down slope usually works well. Always extend the downspout from your house, keeping in mind your site should be at least 10 feet away from the house — farther, if the slope of the overflow lawn area heads towards a house or other important structure that can't be flooded.

Tips

• Locate rain gardens outside of a tree's drip line to avoid cutting into the tree’s roots.

• Don't place the rain garden near or over a septic system.

• Don't locate it in a spot where water pools after a storm, or is constantly wet through the winter.

Just how big should your new rain garden be? A small one won't capture as much storm water and will overflow more frequently, but will still benefit water quality. A general rule of thumb for most homeowners is 100 to 300 square feet or 10 percent of the area draining to it.

If your soil has a high clay content, adding wood chips or compost will help permeability. If you have an impermeable surface area you're not ready to tackle quite yet, you can also install a container garden. Native plants are a good choice. Also, avoid the use of potting soils, which often contain fertilizers.

Good native plant choices for shaded rain gardens include coastal strawberry, False Solomon's Seal, Fringecup, Salal, Sword Fern, Wood Sorrel and Western Bleeding Heart.

For sunny locations, try Common Camas, Douglas Aster, Oregon Iris, Western Columbine, Huckleberry or Thimbleberry (both sun or part-shade), and Yarrow. For additional plant choices try hopping on the Internet or pay a visit to your favorite native plant nursery.

Lastly, installing a rain garden is one positive step we can take to make a difference in the environment and in your local community — but planting one does take effort. Don't be afraid to enlist help from family, neighbors and friends. You'll have fun putting it in and maybe even start a trend in the neighborhood.

If you're uncertain about your soil type or how water will drain given the landscape, look for a landscape business that advertises rain garden know-how.

For more information:

• Oregon Rain Garden Guide

>seagrant.oregonstate.edu/sgpubs/onlinepubs/h10001.pdf

• Choose the Right Rain Garden

>extension.oregonstate.edu/stormwater/choose-right-rain-garden-0

Cynthia Orlando has a degree in forest management and is a certified arborist with the Oregon Department of Forestry.