Physocarpus

( fiss - oh - KAR - puhs )

At-A-Glance Information

Commonly called Ninebark, this genus of deciduous shrubs needs either sun or shade and moderate to regular water. Their common name refers to the peeling quality of their bark, which strips off to reveal many layers underneath. Flowers bloom in clusters of white or pink during spring and early summer months. These are versatile plants that provide seasonal foliage color and are great in mixed beds, as formal hedges, and as background foliage.

Physocarpus Species and Varietals

The genus Physocarpus is a close relative of Spirea, and includes 8-10 distinct species. It is a member of the plant family Rosaceae. Ninebark growing zones vary depending on the species; for more information, see the descriptions below. To find your zone, click here: Zone Map.

Physocarpus capitatus (Pacific Ninebark, Tall Ninebark)
This species of Ninebark grows well in zones 2b-9 and 14-19 and is native to the mountain ranges of western North America. Reaches 5-10 feet tall and wide and produces dense clusters of white flowers that open from buds that are just as attractive as the flowers themselves.
Physocarpus opulifolius (Common Ninebark, Atlantic Ninebark, Eastern Ninebark, Ninebark)
This species of Ninebark grows well in zones A1-A3, 1-10 and 14-17, native to eastern and central North America. Reaches 9 feet tall and 10 feet wide, with white to pink clusters of flowers. Varieties are more attractive and more commonly grown than the species. They are listed and described below:
'Diabolo'
9-12 feet tall and just as wide, with red-purple foliage. Better color in sun.
'Luteus'
Foliage is yellow in sunlight and yellow-green in shade; reaches 9-12 feet tall.
'Center Glow'
6-8 feet tall and wide, with green-gold new foliage that matures to burgundy.
'Coppertina'
6-8 feet tall and just as wide, with copper-orange foliage.
'Dart's Gold'
This variety reaches 4-6 feet tall and wide with bright yellow-green foliage.
'Summer Wine'
Dark purple leaves on a compact plant 4-6 feet tall and wide.
'Nanus'
Foliage is dark green, leaves are lobed. Compact variety.
'Lady in Red'
Purple-red foliage on a compact plant reaching 4-6 feet tall and wide.
'Nugget'
Leaves begin golden-yellow and mature to lime green, turning gold again in fall.

Caring for and pruning Physocarpus shrubs

Plant Ninebark shrubs in full sun to partial shade. Check sun exposure requirements for your specific shrub before planting, as they vary depending on what species you have. Ensure that the soil is fertile, loamy, and slightly acidic to neutral (between 5.0 and 8.0). After planting, water regularly to ensure the shrub establishes a strong root system. Once mature, provide consistent moisture. Although these plants are relatively drought-tolerant, they will look better with regular water. As a rule of thumb, water deeply when the top inch of soil becomes dry. Apply mulch around the bottom of the plant (leaving a few inches bare close to the main stem) to increase soil moisture retention. In early springtime, apply a feeding of a balanced, slow-release fertilizer to support the season's foliage and flowering. These shrubs are generally low-maintenance when it comes to pruning; simply remove dead or damaged branches in late winter or early springtime. For older, established plants in need of a rejuvenation, cut older stems to the ground (about 6-8 inches tall). This will encourage vigorous new growth to emerge in springtime.

Propagation

Physocarpus can be propagated either by using cuttings or from seed. To ensure that your propagated plant will have the exact same qualities and characteristics as the parent plant, use the cutting method. If you would like to experiment and see what plant you can grow from seed, just keep in mind that it will not necessarily be the same as the parent plant. To propagate your shrub, follow the instructions below:

Propagating Physocarpus by Cutting
  1. Gather your materials. You'll need a clean, sanitized, sharp pair of garden shears, a pencil, and a 3-inch pot filled with well-draining compost or other organic material. If you don't have any potting medium on hand, you can make some. Just mix together equal parts (by volume) moss peat and horticultural-grade sand or grit sand.
  2. In spring or early summertime, choose the plant that you'd like to propagate. Ensure that this plant has had a good watering the night before, as this will improve the chances your cutting will take root. Cut one or more 6 inch softwood portion(s) of the end of a non-blooming branch and strip the leaves off of the lower half. Make a hole in your planting medium by pushing your pencil into the soil. Place your cutting in the hole and fill in soil around the cutting to support it, but do not pack it down too much.
  3. Moisten with water, and ensure that the pot has good drainage. Your pot should be kept in warm, sunny conditions indoors (and not in direct sunlight). Water whenever your soil is dry under the top layer. After about four to six weeks have passed, your cutting should be rooted. When you notice new growth, you'll know you have roots.
  4. Keep your new plant in an area with bright light (though not direct sunlight) and temperatures between 55 and 70 degrees Fahrenheit. Ensure that the soil stays moist, but not wet, until the next spring, when you can transplant it to its new home. Ensure that the last frost of the year has occurred before doing this, as it can seriously damage your new shrub.

Propagating Physocarpus by Seed
  1. Keep in mind that the plant you get from seed will not necessarily mimic all of the characteristics of the parent plant. To propagate by seed, you will need a paper bag, a pot or tray filled with well-draining compost or other organic material, a spray bottle and a fork. If you don't have any potting medium on hand, you can make some. Just mix together equal parts (by volume) moss peat and horticultural-grade sand or grit sand. You will also, after a few weeks, need individual 3-inch pots for each seedling that grows.
  2. Harvest your seeds. The seed pods on Physocarpus plants are pretty easy to spot, they're large and are left behind after flowers have faded. Once they have dried out and begun to split open, you can harvest the seeds inside. Cut them off of the plant, placing them in a paper bag. Harvest as many as you can, and place the paper bag in a dry, cool, dark area. They will begin to split open and release the seeds contained inside. Once they have been released, take them out of the bag and put them in a container so you can work with them.
  3. Water your prepared seed tray or pot filled with soil, and ensure that good drainage is occurring. Place your seeds in your prepared pot or seed tray about a quarter inch to a half-inch under the soil surface. Cover them with soil and water with your spray bottle. Place your tray of seeds in a warm area that receives bright, indirect light. A greenhouse is the most ideal climate, but a planting tray inside a window will do as well. Germination usually takes 3-4 weeks from sowing. Once you begin to see seedlings sprout and they are able to be handled, transplant them to their own individual 3-inch pots, filled with the same potting medium as described in Step 1. Loosen the seedlings from the potting medium by digging down with the tines of your fork about an inch and a half, gently working the seedling up until it is out. Then, replant the seedling in its individual pot.
  4. Keep the seedling's potting medium moist, but not wet, by spraying the soil with your spray bottle. Keep your new plant in an area with bright light (though not direct sunlight) and temperatures between 55 and 70 degrees Fahrenheit. Ensure that the soil stays moist, but not wet, until the next spring (after the danger of frost has passed), when you can transplant it to its new home.
Dried seed pods on a Physocarpus shrub.
Physocarpus seeds.

Problems and Pests

Ninebark shrubs are susceptible to the following issues:
  • Aphids
  • Powdery Mildew
  • Fireblight
  • Leaf Spot
For information on treating these issues, check out the following links:
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Gallery

Physocarpus flowers are commonly white and bloom in clusters.
Use these shrubs to add colored foliage to mixed beds.
Some Physocarpus shrubs have a slight graceful, weeping habit.

Videos

How to prune your Physocarpus shrub.
How to transplant mature Physocarpus shrubs.
How to grow Physocarpus as a hedge.
All about Common Ninebark (Physocarpus opulifolius).

Resources

How to Grow Physocarpus
How to Plant and Grow Ninebark (Physocarpus)
Solving a Taxonomic and Biogeographic Puzzle with Physocarpus
Wikipedia: Physocarpus opulifolius
Wikipedia: Physocarpus capitatus
Wikipedia: Physocarpus
The New Sunset Western Garden Book: The Ultimate Gardening Guide (2012) - Page 503, Physocarpus 
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