By Polly Keary, Editor
Stormwater runoff is the single largest source of pollution affecting the Puget Sound, and 70 percent of that runoff comes from non-point sources; that is, sources not traceable to a single business or area.
Most of that water comes from residential and commercial areas.
So in an effort to clean water before it gets to the ocean, the WSU Extension of Snohomish County and Stewardship Partners are working together on a project called “12,000 Rain Gardens by 2016.”
That means that, if you want to install a beautiful rain garden on your property, you can get free help to do it.
A rain garden is a depression on your property that is positioned and planted in such a way that it collects rainwater and cleans it before it runs off your land.
“It is designed to filter stormwater runoff pollution, recharge groundwater and provide wildlife habitat,” said Philomena Kedziorski, Rain Garden Program Coordinator at the WSU Extension office in Bothell.
There is a science to creating a rain garden, and to guide gardeners through the process, WSU offers a handbook either in PDF form available at www.snohomishcd.org or in person at the WSU office, located at 600 128th St. S.E., Everett, just north of Mill Creek.
This is the perfect time of year to build a rain garden, as the soil is too wet to dig in winter, and the ground is too dry to plant in summer.
To begin, make note of where all the impermeable surfaces on your grounds drain. A good site will be at a low point that could serve as a collector for those surfaces. It must be at least 10 feet from building foundations, and it won’t work well if the slope above it is steeper than 15 percent.
Plan to make the garden about 10-20 percent of the area of the impermeable areas that will drain into it. So if you have a large driveway of 600 square feet and a roof of 800 square feet, you might want a 140-280 square-foot garden.
To make sure your soil can adequately drain stormwater, dig a hole two feet deep and fill it with water, then stand a ruler in it. It should drain at least half an inch an hour.
If the soil is good, then you can proceed. Rain gardens should be about 18-24 inches deep, with sloped sides.
The garden is planted in three zones, Zone 3 being the bottom, Zone 2 the sides and Zone 1 the edges.
“At the bottom of the rain garden you plant emergents, plants that will tolerate periods of standing water and short droughts,” said Kedziorski. Included should be evergreen shrubs to hold weeds down.
Sedges are also a good choice, as are shrubs like red-twig dogwood.
On the sides in Zone 2, a wider variety of plants can be used, as long as they can handle a little drought now and again.
And Zone 1 plants should be drought-resistant.
Unless you are experienced with the various plants appropriate for the zones and have a good sense of design, you would do well to contact the Master Gardener Program or the Snohomish County Conservation District for free assistance.
“We have rain garden mentors,” said Kedziorski. “Master Gardeners will help with site assessments, choosing plants, and they’ll advise on maintenance of plants and problems you may have with your plants.”
To arrange a consultation with the Conservation District, call (425) 335-5634, ext.102. To reach the Master Gardeners, call Philomena Kedziorski at (425) 357-6037.
Local landscapers who are well-versed in rain garden installation include Harmsen & Associates, Inc. (360) 794-7811 and Falling Water Designs in Monroe. Visit http://fallingwatergardens.com/.
Woods Creek Nursery in Monroe is also expert in plant selection for rain gardens. Call (360) 794-6823.