Common ninebark (Physocarpus opulifolius) is a plant species most commonly found in the eastern United States. Common ninebark is generally planted for erosion control and ornamental purposes. Several cultivars, such as Dart’s Gold and Diabolo, have received the Royal Horticultural Society’s Award of Garden Merit.
I. Appearance and Characteristics
Physocarpus opulifolius, known as common ninebark, Eastern ninebark, Atlantic ninebark, or simply ninebark, is a species of flowering plant in the rose family Rosaceae, native to eastern North America, named for its peeling multi-hued bark
It is a mound-shaped deciduous shrub with alternate, simple leaves, on arching stems. It has a height from 1–3 m (3–10 ft) and a spread of 1–2 m (4–6 ft). The leaves vary from 3–12 cm (1–5 in) in length, with palmately veined lobes. It is fast-growing, insect- and disease-resistant, and drought-tolerant. The species is adaptable to a very wide range of soil and site conditions, from moist to dry, acid to alkaline, and gravelly to heavy clay; and can grow in partial shade to full sun.
The 5-petaled, 6–8 mm (0.24–0.31 in) diameter flowers form in corymbs. The flowers are white to pinkish, blooming from May to June in North America. In Missouri the fruits ripen from August to early October and are small, dry pods hanging in drooping, papery clusters. The bark peels off in thin papery strips, resembling the number nine in shape, exposing brown inner bark which is the origin of the common name.
It is a larval host for the dimorphic eulithis, for Macaria abruptata, the white spring moth, Ancylis spiraeifoliana, the blinded sphinx moth, and possibly the bluish spring moth. The larvae of the raspberry leafroller have also been recorded on this plant.
II. How to Grow and Care
Sunlight
Plant ninebark in a location that receives full sun to part shade, taking note that it will flower best in full sun. In northern latitudes, the shrub prefers around six hours of direct light each day, but in the far south, the plant appreciates some afternoon shade.
Temperature and Humidity
Ninebark is typically tolerant of the various temperatures and humidity levels within its recommended hardiness zones, but the plant will not do well in zones 8 and above due to the South’s extreme summer heat and humidity. Growing ninebark in a hot and humid environment makes it susceptible to fungal diseases, like powdery mildew.
Watering
Ninebark will grow in both dry and wet locations. Its water requirements are generally low, but it can deal with poor drainage and occasional flooding. Once established, ninebark is a very good drought-tolerant shrub for dry areas.
Soil
This shrub prefers a neutral to slightly acidic soil that drains well, but it will tolerate slightly alkaline soils, as well. Provide mulch around the base annually to help the plant retain moisture and to prevent weeds. Ninebark’s native habitat includes stream banks, hillsides, and damp thickets, allowing the plant to grow well in clay and loam soil, as well as shallow and rocky soil.
Fertilizing
Spring is the best time to add compost and organic plant food to your ninebark shrub. Make sure to use a product specifically for shrubs and trees, and one annual feeding is all that is required. Apply fertilizer to the soil starting a few inches away from the shrub’s trunk, and then spread it out in a thin layer around the base.
Planting Instructions
Planting requirements for ninebark are similar to any woody landscape shrub. Dig a hole as deep as the nursery container and twice as wide. Plant the shrub so the top of the root ball is exactly at ground level, and then backfill the root ball, making sure there are no air pockets. Poor soil can be amended with organic material before filling the hole. Water thoroughly after planting.
Pruning
Prune ninebark after it flowers, or no later than mid-August, to maintain its shape and to improve air circulation around the plant. One-third of the branches can be cut with each pruning, focusing on older and damaged branches, as well as those that cross and rub each other.
Older shrubs can be radically pruned close to the ground before winter to encourage better leaf and flower growth come spring. Ninebark tends to bounce back well after pruning.
Propagation
Woody shrubs can be tricky to propagate, and it can take quite a while (sometimes a year or more). However, stem cuttings from ninebark are relatively easy to root. You need to do so when the plant is dormant.
To propagate by cuttings:
- Gather your pruning shears, rooting hormone, a zippered plastic bag, and sphagnum moss or wood shavings
- In late fall or early winter, cut several pieces of hardwood branch (not softwood tips) from your shrub. Make cuts about 1/2 inch thick and 4 to 6 inches long. Each cutting should have at least two nodes (bumps on the branch where leaves sprout). Make the bottom cut just below a node and the top cut about 1/2 inch above a node.
- Dip the bottom of each cutting in rooting hormone. Gather the cuttings together and secure them with a rubber band.
- Place the bundled cuttings in a plastic bag filled with slightly moist sphagnum moss or wood shavings. Store the cuttings in the refrigerator to keep them dormant.
- In early spring, as soon as the ground can be worked, separate the bundled cuttings and plant them in the soil, making sure the tops are facing up. Bury them so that all but the top nodes are below ground.
- Water the cuttings regularly. They will require a full growing season to develop roots, but in late fall or early spring, your fully rooted cutting will be mature.
To propagate straight from the mother plant (layering):
- Gather a shovel and pruning shears
- Bend down one of the flexible branches of your mother plant so that a portion of it is buried in the soil, leaving the tip of the branch exposed. When secured in place, the buried portion will send out roots from its nodes.
- Once the branch has developed ample roots (it can take a full growing season), snip it free from the mother plant and transplant the rooted cutting elsewhere.
How to Grow from Seed
Ninebark shrub is best propagated from cuttings, however, you can sow seeds collected in the fall. To do so: In the spring, combine a mixture of peat, pine bark, sand, and perlite in a 5-gallon bucket; add water until it feels moist. Divide the mixture into 5-inch pots and sow two seeds per pot at 1/8 inch depth. Cover with a dusting of the mixture and heavily mist the top. Place the pots outdoors in a sheltered, lightly shaded area where temperatures will not drop below 50 F.
Maintain moist soil until the seeds start to germinate (this can take three weeks to two months), and then pluck the leggier of the two seedlings in each pot to allow the other to grow all summer long. In the fall, bring the pots indoors until the following spring when the baby shrubs can be planted outside in the ground.
Overwintering
Before the first frost, prepare your ninebark bush for winter by pruning back any dead or broken branches. Some gardeners like to keep the bush intact, as the peeling bark and turning leaves add to the garden’s winter aesthetic. Others like to cut the bush 3 to 4 inches from the ground. Continue watering the plant through the fall, and cover the base with mulch before the plant reaches its winter dormancy.
Pests and Diseases
Common Pests & Plant Diseases
Ninebark shrub is susceptible to aphids, which can be controlled by spraying the plant with a steady stream of water to knock off the pests, or by misting the shrub with neem oil or another organic spray. With proper upkeep, established ninebark shrubs are free of most problems. Fireblight, powdery mildew, and leaf spots may occur, but are rarely fatal. Badly damaged branches can be pruned away to avoid most diseases.
Common Problems
This hardy plant has very few issues, however, it can fall susceptible to leaf curling and wilting with improper care. In order to prevent this, make sure your plant gets enough water and sunlight, and prune it back and mulch around it before winter.
III. Types of Ninebark
The ninebark shrub comes in several varieties with different colored leaves, the most common being purple and yellow.
- ‘Diablo’ (also known as ‘Monlo’) is an 8- to 10-foot-tall shrub with burgundy foliage. It flowers in late spring and grows best in zones 3 to 7.
- ‘Little Devil’ (also known as ‘Donna May’) is a dwarf variety that grows 3 to 4 feet tall with greenish burgundy foliage. It blooms early in the summer and is known for its mildew resistance. This plant is hardy in zones 3 to 7.
- ‘Center Glow’ grows best in zones 3 to 7 and is one of the more colorful ninebark varieties. This 6- to 8-foot-tall shrub yields greenish-gold spring leaves that gradually mature to a deep burgundy later in the summer, and white flowers.
- ‘Dart’s Gold’s’ leaves turn bright yellow in spring, and then mature to a deep chartreuse in the summer. Come fall, the leaves develop a tinge of bronze. This shrub grows 4 to 5 feet tall with white spring blooms, and is hardy in zones 3 to 7.
- ‘Amber Jubilee’ grows 5- to 6-foot tall with orange-yellow spring leaves that turn purple in the fall. Hardy in zones 2 to 7, this variety flowers with white blooms in the late spring.
IV. Uses and Benefits
Common ninebark is a hardy plant that can tolerate poor conditions and is suitable for rock gardens. It can also help prevent soil erosion on slopes. Its dense foliage and charming, round flowers are decorative and look particularly good in large clumps. Garden phlox, coneflowers, and Russian sage make good companion plants that do not compete for resources.
