Plant of the Month: Pacific Ninebark
I’ve become a fan of our native ninebark, Physocarpus capitatus. It’s a big, glorious shrub. As the common name implies, the shredding bark provides year-around interest whether it really has nine layers or not. In June it is covered with ball-like clusters of small white flowers, held just above the dark green foliage. Birds eat the mature seeds in late summer and in autumn the leaves turn golden.
Ninebark grows best in sunny to partly sunny areas with plenty of moisture and rich soil. In the wild, you’ll find it along streams, lakeshores, the edges of marshes, and roadside ditches. We’re going to plant it in the wettest part of our yard as soon as I finish getting the blackberries cleared out.
Full grown, ninebark can reach twelve feet tall and form dense thickets, providing valuable cover to small birds and mammals. While not totally immune to deer browsing the foliage, it’s less palatable than many other shrubs and vigorous enough to withstand a little pruning. Like most other shrubs in a garden setting, some judicious pruning will keep ninebark to a manageable size and shape.
Pacific ninebark is native to the west coast from Alaska to California, primarily west of the Cascades but also in northern Idaho and the Sierras. It is found at low to middle elevations. Like many other northwest shrubs, ninebark tolerates both summer drought and our wet winters. It even accepts standing water in the winter.
Ninebark is a member of the rose family. Look closely at the individual 5-petaled blossoms and you’ll see that they look like miniature rose flowers.
There are other species and cultivars of ninebark. The east-coast native, Physocarpus opulifolius, has been extensively hybridized and several garden cultivars are commonly available. Mallow ninebark, Physocarpus malvaceus, is another west-coast native. It grows primarily east of the Cascades in drier habitats and does not become as large as Pacific ninebark.
You’ll find Pacific ninebark in my books on page 249 of Trees and Shrubs of the Pacific Northwest and page 132 of Wildflowers of the Pacific Northwest. Photos of both of our western ninebark species are on my wildflowers website. There’s a nice profile, with additional gardening information, on the Washington Native Plant Society website.