Chapter 115 Physocarpus opulifolius
115.2 Soil: Moist Deciduous Mix
Ratio: 4 parts bark, 1 part grit
Add-ins: dolomitic limestone (~5 lbs/yd), Tree-Tone (15 lbs/yd)
pH: ~6.5 (slightly below neutral)
Moisture: prefers moist soil that gets good drainage.
115.3 Light
Routine: full sun when weather is cool.
Summer: some afternoon shade in heat of summer.
115.4 Cultivation Notes
Tends to struggle in hot and humid summers. Ninebark blooms on parts of the branches and stems that grew the previous year—not on the new growth from the current year.
115.4.1 Potting & Root Pruning
Schedule: repot in spring.
115.4.1.1 Top & Branch Management
Ninebark should be pruned early in the growing season. The best time to prune a ninebark shrub is immediately after it flowers (late winter to early summer, depending on location and cultivar).
Remove no more than a third to half of branches and foliage each year.
Heavy pruning: cut away branches that are dead, damaged, broken, or diseased. Then remove branches as needed to ensure there’s enough room in the interior of the plant for air to circulate and sunlight to reach the inner foliage. Also remove spindly or weak shoots that sag or produce fewer leaves than others on the plant.
Fine pruning: limit late-season pruning. After midsummer, ninebark goes into dormancy and pruning during the plant’s dormancy can damage it.
Leaf pruning: not appropriate for this species. Summer dormancy prevents them from leafing out a second time.
115.4.2 Feeding
Feed in spring when buds begin to emerge with all-purpose (10-10-10 or similar) fertilizer. Do not fertilize while in summer dormancy.
115.4.3 Pests & Problems
No serious insect or disease problems. Fireblight and leaf spots may occur.
115.4.4 Winter Storage
Store in mulch outdoors. Try to place in a shaded area so buds do not break in a mid-winter warm spell. No other special precautions are needed.
115.5 Propagation Notes
Cultivars are available in garden centers. They are easily started from seed, but plan for several years’ growth before they are ready to start styling.
115.6 Artistic & Styling Notes
115.7 Additional Information
115.7.1 Natural History
Ninebark is native to eastern North America. It is an upright, spreading, somewhat coarse, deciduous shrub that is closely related to the genus Spiraea. It is fast-growing, insect- and disease-resistant, and drought-tolerant.
Ninebark reaches maturity at six to 10 feet tall and wide in USDA Zones 2-7. Clusters of white 5-petaledd flowers appear in late spring. Drooping clusters of reddish fruit provide fall interest. Winter interest includes exfoliating bark on mature branches which peels in strips to reveal several layers of reddish to light brown inner bark.
115.7.2 In Cultivation
‘Diabolo’ is a purple-leaved ninebark cultivar. Small pinkish-white, five-petaled flowers in dense clusters.