Viburnums have long been one of the most popular flowering landscape shrubs. With an almost infinite number of viburnum cultivars available, you can find one to suit any garden. For most viburnum shrubs, bloom times span from early spring through June, followed by attractive fruit and outstanding fall foliage. Fast-growing viburnums can be grown as either shrubs or small trees.
There is no single type of viburnum foliage. It can be rounded, lance-shaped or toothed, smooth, velvety, or rough. There are some evergreen viburnum varieties, in addition to many deciduous varieties with outstanding fall color. The flowers come in three major types: flat clusters of florets, flat umbels outlined with larger flowers resembling lace-cap hydrangeas, and dome-shaped, snowball-like clusters.
|Common Name||Viburnum, American cranberry bush, hobblebush|
|Botanical Name||Viburnum spp.|
|Mature Size||3-20 ft. tall, 3-12 ft. wide|
|Sun Exposure||Full, partial|
|Soil Type||Moist, well-drained|
|Soil pH||Neutral, acidic|
|Flower Color||White, pink|
|Hardiness Zone||2-9 (USDA)|
|Native Area||North America|
In general, viburnums are not particular about where they grow, though they prefer fairly rich, moist soil. Viburnums do not transplant well once established, so the best strategy is to plant well-established container-grown plants and take care to choose a location where the shrub will have room to grow. Early spring is the best time for transplanting, giving them a full season to adjust.
To plant viburnum, dig a hole as deep as the container and twice as wide. Gently remove the plant from the container and place it in the center of the hole. Backfill the hole halfway, add some water, then fill the hole completely.
After planting, add a 2-inch layer of mulch to keep the soil moist and hold in moisture. During hot weather, the shrubs should be watered every 7 to 10 days. Little pruning is necessary, though some species can be trained to form tree-like plants by removing competing stems.
Viburnums prefer full sun but will tolerate part shade. In fact, some afternoon shade is desirable in the warmer zones of the plant's hardiness range.
These shrubs prefer fairly moist, well-drained soil, but they do not like to have their roots soaking in water. Viburnums like slightly acidic soil but many types will tolerate alkaline soil.
A deep watering every week is usually sufficient, either through rainfall or irrigation. Native varieties that are well-established have a fairly good drought tolerance.
Temperature and Humidity
Viburnums prefer moderate conditions, though the preferences vary greatly depending on species. Extremely hot weather requires extra watering, and very cold temperatures can stunt the plant or cause dieback.
Most viburnums need little more than one application each year of a balanced, time-release fertilizer mixed into the soil in spring. For the amount, follow the product label instructions. Once established, most shrubs do well without any feeding.
Types of Viburnum
- 'Nannyberry' (Viburnum lentago): This species grows in USDA hardiness zones 2 to 8 to a mature height of about 12 feet with a 10-foot spread. It prefers moist shade but will weather hot sun and dry soil. Lace-cap flowers in creamy white appear in mid- to late-May.
- 'Swamp-haw viburnum' (Viburnum nudum): This plant grows in zones 5 to 9, where it achieves a mature height of about 12 feet with a 6-foot spread. It prefers a location with full sun to partial shade. This variety produces white flowers in late June, followed by clusters of round drupes.
- 'Hobblebush' (Viburnum lantanoides): Formerly known as Viburnum alnifolium, this variety grows in USDA hardiness zone 4 to 7. It achieves a maximum height of about 8 feet with a spread of 12 feet. A native to northeastern to mid-Atlantic North America, it tends to grow a bit disorderly and is probably best suited for a naturalized setting. Flat umbels of white flowers appear in May, followed by red fruit clusters that age to the typical blue-black.
Leggy shoots can be trimmed back in early summer to maintain the shrub's form. As viburnum blooms on old wood, pruning should be undertaken only after the bloom period. Broken, dead, or diseased branches should be removed as soon as you notice them. Tree forms of this plant may require some pruning to achieve the desired shape.
You can propagate viburnum from softwood or hardwood cuttings.
- For softwood cuttings, choose a vigorous branch of 4 to 6 inches in length. Take the cutting in the morning, if possible. Remove leaves from the lower third. For hardwood cuttings, choose a strong stem and cut 8 to 10 inches of it, stripping the leaves from the bottom half and making sure to include at least a few nodes.
- Fill small pots with a moist mixture of peat and perlite and make a small hole in the center of the mix.
- Dip the stem in rooting hormone. Plant the cutting in the pot.
- Cover the cutting with a plastic bag or dome and keep it in indirect light, with damp soil, until the roots begin to form in about four weeks for a softwood cutting. Rooting might be slower for a hardwood cutting but should still occur within a few months.
- Test for rooting by pulling gently on the plant. If there's resistance, the plant is beginning to establish roots. Remove the plastic and place in a spot that provides bright indirect light. Before planting in the landscape, gradually acclimate your plant to the outdoors by placing it in a protected area for a few hours every day for a week or 10 days.
How to Grow Viburnum From Seed
Growing viburnum from seed can be done, but it's a laborious process. Most experts suggest propagating from cuttings instead.
Potting and Repotting Viburnum
Carefully choose your cultivar for planting in pots; some types of viburnum must have the space an outdoor planting provides, while others are ideal for smaller habitats. Plant the viburnum in large containers with drainage holes; the pot should be at least 8 inches wider than the root ball. This plant needs well-draining soil and full sun. To avoid soggy soil, add 10%-20% perlite to the mix.
Viburnum is hardy but might drop leaves in colder weather. Prune off dead leaves and branches. Come spring, your shrub will recover.
Common Pests and Plant Diseases
The fact that few pests bother viburnums is one of the reasons they have become so popular in the landscape. However, in 1947 the viburnum leaf beetle (VLB) arrived in Canada and made its way to New York state in 1996. The VLB, Pyrrhalta viburni (Paykull), is capable of great damage and is being closely watched. The best way to combat viburnum leaf beetles is to remove egg-infested leaves and encourage predatory insects. Some organic pesticides are also effective, but avoid synthetic pesticides, which also kill beneficial insects.
How to Get Viburnum to Bloom
If your viburnum is not blooming, look at the location—though it can handle some shade, those kept in full sun will form blooms more readily. Watering might also be an issue, as viburnum needs to be in well-drained soil. Remember that too much nitrogen can encourage lush foliage but stunt the explosion of blooms. Since the plant blooms on old wood, don't trim them during dormancy, as this will eliminate the bloom-producing buds.
Common Problems with Viburnum
Fortunately, viburnum has few issues for gardeners to contend with. However, if you notice any of the following, treat the problem immediately to ensure the health of your plant.
Black Spots or White Growth on Leaves
This is often the result of a fungal disease, such as powdery mildew, downy mildew, or fungal leaf spots. To prevent this, water the plants from overhead, use a fungicide on affected plants, and destroy parts of the plant that are already affected.
Stunted or Yellow Leaves
This might be the result of Armillaria root rot, which can be determined by a white fungal growth under the bark and at the crown of the tree or shrub. If this problem has made its way into the trunk, the only solution is to dig up and discard the viburnum.
Dead, Wilted, and Discolored Leaves
Viburnum could be affected by canker, which is a fungal problem. This often occurs with trees that are already stressed. The most effective treatment is restoring the plant to health, as it can likely fight off this particular issue on its own.
How long can viburnum live?
Depending upon the variety, viburnum can live between 50 and 150 years with proper care.
Where should I place viburnum in my house?
To get the best blooms, keep the plant on a sunny windowsill. You can even do this during the winter, assuming you choose a hardy variety that can handle potential drafts.
How fast does viburnum grow?
This plant can grow between 12 and 24 inches in one year. However, some dwarf varieties are very slow-growing and only clock in at about 6 inches in a year.