Extension Service Garden Hints

Native groundcovers work well in Pacific Northwest landscapes

CORVALLIS, Ore. - West of the Cascades, the Pacific Northwest is famous for being green year-round and for its lush forest undergrowth. You don't see much bare ground, as native groundcovers are naturally prevalent. There are several that work great as native ground covers in the home landscape.

Native or not, groundcovers provide several benefits to the garden, explained Linda McMahan, native plant specialist with the Oregon State University Extension Service.

"Weed suppression is an obvious effect of groundcovers," she said. "Also, having ground covers helps the soil retain water. And an often-unrecognized benefit is protection from soil compaction. The constant patter of little raindrops can compact the soil, not to mention feet and animals."

Using native plants, including ground covers, in your garden makes sense, McMahan says. Foremost, they are naturally suited to your climate.

"As long as you use some common sense about exactly where you locate them in your garden, you shouldn't have to pamper them," she said. "And since native plants have co-evolved with deer and other wildlife, you're also less likely to have them wiped out by a marauding neighborhood doe."

The term "groundcover" covers a lot of, well, ground. It includes low-growing plants that never reach more than a couple of inches in height as well as others that might grow as tall as two feet or more. Some groundcovers, such as bleeding heart, have showy flowers. Others, such as wood sorrel, are grown for their foliage. Most of these plants spread easily, which is why they're called "groundcovers."

McMahan has several suggestions for northwest gardeners looking for natives to plant.

For sunny areas, she likes coastal strawberry (Fragaria chilioensis), with dark-green leathery leaves with white flowers in the spring and tiny fruit in the fall. She also recommends F. virginiana, a Willamette Valley native, for sun and part sun. F. vesca is shade loving, also good for part shade, and is also a native. McMahan has all three in her garden and says they tend to sort out where they like to be.

These strawberries don't need shearing back.

"The only maintenance required is to snip off the runners so they don't run across paths. Or simply walk on the plants – that's a matter of personal taste."

Kinnikinick (Arctostaphylos uva-ursi) is a low-growing evergreen plant that's been a favorite in Pacific Northwest gardens for a long time. It has tiny glossy leaves and reddish woody stems. Although it takes awhile to fill in solidly, eventually it forms a dense cover. But, McMahan says, it's not terribly good at suppressing weeds. They just grow up through it. It likes sun and is somewhat drought-resistant.

Most of the kinnikinick on the market is labeled "Massachusetts," and is not native here. The northwest native kinnikinick can sometimes be found at a native plant nursery.

For shade, McMahan suggests Western bleeding heart (Dicentra formosa), which grows in moist woods. It dies back to the ground in the winter but by mid-spring grows to 18 inches to three feet tall, with hanging clusters of pink flowers. It spreads by rhizomes and seeding. It will die back in the summer if it isn't watered, but watering will extend its season.

Another shade-loving native is the inside-out flower (Vancouveria hexandra). About a foot high, it has small light-green leaflets and looks similar to ivy. "It's a great groundcover," said McMahan. "But it's deciduous. It turns a beautiful yellow in late November and December and re-emerges the next year."

Although it's native to coastal forests, it's also somewhat drought resistant. It spreads slowly, its roots forming a dense mat.

Wood sorrel (Oxalis oregana), spreads by rhizomes and grows to about 10 inches high. It has light-green, three-lobed foliage and white to pink flowers in the spring. It grows well in shade. In colder areas it dies back in the winter. If it doesn't, you may want to mow it to force new growth. It spreads fast and once established, McMahan warns, it is very difficult to get rid of. So it works best not to mix it with delicate plants that it might out-compete. It works well with ferns and under shrubs and trees where a true groundcover is wanted.

Another, taller groundcover is a form of our Oregon grape called the long-leaf Oregon grape. It is Berberis nervosa, which grows several feet tall but can be sheared back every three to five years for an even-height stand. It forms spikes of bright yellow flowers in the spring followed by dark blue berries in summer. It's a birders' favorite, as it produces fruit that they love. (Oregon grape used to be classified as Mahonia and is often still called that.)

It is best to plant natives in the fall after summer's heat has subsided or in the spring.

By: Davi Richards
Source: Linda McMahan

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