Ninebark in the Garden

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Ninebark in the Garden

by Darlene Ward

When our much-desired rain finally arrived, I noticed bright green leaves emerging on the Pacific Ninebark (Physocarpus capitatus). The leaves were especially vibrant in their moist surroundings and, upon closer inspection, there were clusters of buds already showing. I was reminded of the questions I had about pruning last summer. How much? When?

My plant has 8-foot long arching branches with clusters of small white flowers that appear in late spring or early summer. The slender branches tower over my head, pressing outward against the deer fence and back the other way towards my blueberry bushes. Although the plant is decorative at the edge of my vegetable garden, it is somewhat cramped in its space. The Sunset Western Garden Book simply says to prune as needed after bloom and to rejuvenate by cutting old stems to the ground. A search on the Internet suggested leaving the blooms in place in order to enjoy the red seedheads. I did for a while, but then decided to trim out the seedheads because they were hanging on too long. I left the arching branches in place, although I cut back by half the one aiming at the blueberries. It is now sprouting new growth where I made the cut.

A further search provides this advice: ninebark buds form on old wood (last year’s growth). Any trimming or pruning should be done right after bloom and at least before August. Cutting branches back at the end of summer or in the winter will cut off buds, eliminating flowers the next season. Ninebark can be reduced in size by cutting branches back by a third right after blooming. Cut just above a bud and new branches will grow at the location of the cut, creating a fuller look for the shrub. It is not necessary to cut the arching branches back at all if the gardener desires a rangier shrub and there is plenty of space. The old stems can be left to mature and they will reveal interesting shredding, peeling bark in winter when the shrub is barren of leaves. The name “ninebark” refers to the possibility of the stems having nine layers of bark, but it is unlikely that anyone has ever counted that many.

Winter pruning is appropriate to thin the shrub and encourage new growth. Up to a third of the old stems can be cut to the ground in winter when the plant is dormant. These stems can be identified by their more striated bark and larger diameter. Thin, spindly stems can also be eliminated. If the plant looks simply dismal, it can be rejuvenated by completely coppicing or cutting off all of the stems in winter. There will be new growth but no flowers that spring. This shouldn’t be done every year, for it would weaken the plant and eliminate the attractive flowering.

Ninebark is in the rose family and is closely related to spirea. It is native to the Sierra and coastal mountains, extending to other northwestern states and Alaska. It has three season appeal: the shredding bark in winter, flowers in late spring and yellow leaves in fall. We do not eat any parts of ninebark, for some sources say they are poisonous, but we grow ninebark because it is an interesting plant that can be used as a specimen, a screen or part of a mixed border. It often grows in riparian areas, but it will grow in our gardens in sun or shade. Although it likes moderate to regular water, it survives on much less when it is mature. My plant is inside the deer fence, but generally deer don’t eat it. I haven’t observed any insect problems. It is a sturdy plant that seems to accept whatever care is given.

Ninebark can be propagated in various ways: transplanting volunteer seedlings, dividing the basal clump of stems, layering the tip of a young, flexible branch or making hardwood cuttings. It can also be purchased at native plant sales. There is a native groundcover or prostrate form from San Bruno Mountain (south of San Francisco) that is about 3 feet tall and spreading. The eastern North American ninebark has been bred to produce some popular cultivars with gold or purple leaves.

I now have a plan for my ninebark. I won’t prune anything this spring because I want to preserve the flower buds. I’ll cut back some of the arching branches in July (after blooming) to see if my plant can have a fuller look next year, but I will also leave some arching branches because I like that look. Next winter I will examine the old stems and decide if I want to eliminate any. I will also remove those that grow towards the blueberry space. I’ll decide if the plant is spreading appropriately towards its other neighboring plants. When flowers appear, I’ll enjoy the contrasting white petals and pink-tipped exserted stamens and watch carefully to note which insects enjoy them the most.

**A link to a photo of Ninebark in flower.