How does your rain garden grow? Best plants for Northwest


By Linda Weiford, WSU News

PUYALLUP, Wash. – Leave it to Northwesterners to brandish garden gloves and trowels in their attack against water pollution.

Rain gardens – scenic sponges that harness rainwater and filter pollutants – are taking root along public curbsides, in front of businesses and behind homes. In a green movement sweeping the Pacific Northwest, many of these landscaping marvels are being installed with the know-how gained by researchers at Washington State University.

Meaning that, as long it’s carefully placed and holds the right soil mix and suitable plants, you too can have a rain garden, regardless of where in the region you live.

Native plants find use statewide

WSU horticulturist Rita Hummel in front of Oregon grape, an attractive evergreen shrub that grows in the Pacific Northwest and does well in rain gardens. Photo at top shows rain gardens at WSU’s stormwater center at the Puyallup Research and Extension Center near Seattle.

Which plants are suitable? By experimenting on 16 rain gardens at WSU Puyallup’s Research and Extension Center south of Seattle, horticulturist Rita Hummel has figured it out. Whether you live west of the Cascades with more precipitation or east of the range where it’s drier, “certain native plants should do well in either climate when planted in a rain garden that’s properly designed,” she said.

Most rain garden research has been done in the eastern U.S., where the amount of summer rainfall is significantly greater than in the Pacific Northwest, she said.

“Plants that do well there may not do so well here, so our research involves mostly species that are native to our region,” she said. “They have to be able to thrive on a good drenching but also tolerate extended periods of drought.”

Pretty, and for the greater good

Rain gardens look good and are generally low-maintenance. What’s more, they’re workhorses, offering a natural way to fight stormwater runoff, a major source of water pollution nationwide. Rain flowing over rooftops, parking lots and other hard surfaces carries oil, pesticides, animal waste and other toxins into storm drains, streams and rivers.

By installing a rain garden, you can replace the rain-gone-wild scenario with this: Rainwater will be funneled into a shallow depression dug into the ground that’s filled with soil, mulch and vegetation. The water will trickle through the soil and plant root systems and be largely cleansed of pollutants.

Hummel’s approach is a combination of science and creativity. Brimming with ornamental grasses, trees and flowering shrubs, the gardens she planted five years ago on the Puyallup campus silently filter toxins from rain runoff while putting on a nice-looking show for the neighborhood. They also reduce the need for irrigation and provide dynamic habitat for birds and butterflies.

“We’ve been able to demonstrate how rain gardens benefit the environment and beautify the environment at the same time,” she said.

For the list of recommended plants, see

For a step-by-step guide on designing and installing rain gardens, go to the “Rain Garden

Besides conducting rain garden research, WSU has partnered with the nonprofit Stewardship Partners in a campaign to get 12,000 rain gardens built in Puget Sound communities by the end of 2016. For more information, go to


Rita Hummel, WSU horticulturist, 253-445-4524,
Linda Weiford, WSU News, 509-335-7209,