Absorb Thisby Valerie Easton
Seattle Times, January 6, 2008
Why all the buzz about rain gardens? In this soggiest of months, isn't every garden a rainy one? And that's just the problem. We tend to think of water management in terms of conservation, soaker hoses and drought-tolerant plants, but that's only half the equation.
This time of year we're faced with the abundance nature pours down on us. All that liquid falling from the sky is laced with pollutants that run off roofs and pavement into streams, rivers and ultimately Puget Sound. Our gardens are an ideal venue for mitigating the onslaught. A good rain garden collects, absorbs and filters water in much the same way forests used to do.
No matter how elaborate or simple, rain gardens add up to a big environmental plus. British authors Nigel Dunnett and Andy Clayden in their book "Rain Gardens" (Timber Press, $34.95) describe the concept as a linked chain, starting with water collected off the roof of a house, shed or garage and ending with the lowest geographical point on the property. All of the garden's features and plantings are tied into the design and management of stormwater runoff. This sounds a little daunting, but think of it this way: Every feature of your property has the potential to improve the ecology instead of detract from it.
Here's how: Rain gardens help filter oil and grease from driveways, as well as herbicides, pesticides and fertilizers. We can protect salmon by percolating these nasty residues through the soil before they flow through storm drains into waterways and wetlands.
Rain gardens help prevent sewer overflow and urban flooding, as we've had destructive and even tragic examples of here in recent years. When planted in Northwest natives, they provide habitat for beneficial insects and birds. Rain barrels and cisterns collect water off roofs to use in the garden when and where it's needed. Permeability is a key word here. Gravel or mulch slows water passage down, while rain sheets off concrete or asphalt right into the storm drains. There's even the option of permeable paving where you need a solid surface.
It's not hard to get started. The city of Seattle has a couple of pilot projects going and hopes to start a residential rain-garden program within the year. In the meantime, you can begin by simply noticing where water naturally puddles on your property and taking advantage of that. There are formulas for figuring out soil drainage (see the book mentioned above). The point is for water to be held for a bit in the soil, and many gardens already have low-lying, boggy areas that do just that. If not, you can create one by digging 4 to 8 inches into a basin shape that collects rain. Just be sure to locate your rain garden at least 10 feet away from foundations of buildings. Avoid septic tanks and drain fields, and don't dig near the edge of steep slopes. For maximum impact, you can direct water flowing off a roof or driveway through a swale or pipe to your rain garden.
Amending the soil with compost and topping off with mulch makes all the difference in slowing down water's passage. To learn more, see www.soilsforsalmon.org, a site rich with information on soil-building practices. Finally, once the soil is ready, it's time for the plants. We have plenty of attractive natives that thrive in damp conditions, like red twig dogwood, rushes, sedges, salmonberry and twinberry. Ornamentals that put up with wet feet, such as royal ferns, big-leaved ligularias or various primroses, add seasonal interest and color. Plant your rain garden generously, and no one would ever guess that this water-filtration system and nature habitat is anything more than a lush, beautiful landscape feature.
Visit www.pierce.wsu.edu/water_quality/LID for a detailed, downloadable pamphlet called "Rain Garden Handbook for Western Washington Homeowners" or call the Natural Lawn and Garden Hotline at 206-633-0224 to order a hard copy.
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