Chinese snowball viburnum has a medium growth rate; 1 to 2 feet per year is typical. It is normally planted as a potted nursery specimen in the fall. Plant the shrub in a well-prepared hole at the same depth it was in its nursery container, and keep it very well-watered for its first year. Dense clay soils should be amended with plenty of organic material (peat moss, compost) before planting. This is a large shrub so space them at least ten feet apart. This shrub is especially good at resisting the common bacterial leaf spots and fungal diseases such as powdery mildew that plague other viburnum species, and it has virtually no serious insect or disease problems.
Light
Chinese snowball viburnum can tolerate full sun to partial shade conditions, but for optimal flower production, it requires at least six hours of full sun each day. Too much shade will cause the blooms to become sparse and the shrub to become leggy.
Soil
This beautiful shrub needs well-drained, slightly acidic soil for best performance. However, it is tolerates a wide range of soil conditions and it even tolerates slightly alkaline soil. Avoid soils that hold onto too much water, as Chinese snowball viburnum does not like to be waterlogged.
Water
Keep the soil evenly moist throughout the year. Depending on the temperature in your area, the watering schedule will vary, but determining and sticking to a watering schedule will help the Chinese snowball viburnum produce the most stunning show of blooms. Be wary of overwatering, though, especially if the plant is growing in dense soil. A mature shrub can tolerate some drought.
Temperature and Humidity
While there are other viburnum species that are suitable as far north as USDA hardiness zone 2 or as far south as zone 10, Chinese snowball is best in more moderate climates, zones 6 to 9. It can survive winter temperatures down to about minus 5 degrees Fahrenheit, but it struggles in extremely hot climates, where it might need to be shaded from the intense rays of the sun and require more water than usual. It tolerates both arid and humid atmospheric conditions, provided soil moisture is adequate, but it may be susceptible to mild fungal disease issues in very humid conditions.
Fertilizer
Fertilize Chinese snowball viburnums at planting, and then annually, immediately after the shrub has finished flowering. For best results, use an all-purpose balanced fertilizer that is formulated for woody shrubs.
Types of Chinese Snowball Viburnum
You might see this plant sold as Viburnum macrocephalum ‘Sterile’, but there are no other named cultivars of Chinese snowball viburnum. The wild form is sometimes known as V. macrocephalum f. keteleeri, and it is less showy than the cultivated variety usually sold commercially. Here are some hybrid viburnums that have V. macrocephalum as one of its parents:
Viburnum macrocephalum x V. carlessii is known as fragrant snowball. It has heart-shaped leaves but smaller flowers than V. macrocephalum. Blossoms are fragrant and the plant is hardy as far north as USDA zone 4.Viburnum ‘Nantucket’ is a smaller hybrid crossed between V. x ‘Eskimo’ and V. macrocephalum f. keteleeri. It is another snowball viburnum, but it does not have the excellent disease resistance of Chinese snowball. It is hardy in zones 6 to 9.
Pruning
After flowering, the Chinese snowball viburnum can benefit from some light pruning to shape the shrub and remove dead or diseased branches. Ideally, this shrub has a classic vase-shaped growth habit with a rounded top, and pruning efforts should be aimed at maintaining that shape. It is also possible to train the plant as a small tree by systematically favoring a large central leader while trimming away lower offshoot branches. Every three or four years, this shrub can benefit from a more severe pruning that cuts the stems down to 2 to 3 feet, which will control the size and prompt plentiful new growth. You should expect that growth will be slightly stalled during the first growing season following a heavy pruning, but very vigorous in the following years. If you are planning a hard rejuvenation pruning, winter is a good time to perform this task.
Propagating Chinese Snowball Viburnum
Chinese snowball viburnum produces sterile flowers, so the best way to propagate it is by softwood cuttings. For best results, take cuttings in the spring from shoots with vigorous new growth. Here’s how:
Overwintering
Chinese snowball viburnum requires no special winter protection, provided it is growing within its established hardiness range. Zone 6 gardeners might want to provide some form of windbreak against harsh winter winds.
How to Get Chinese Snowball Viburnum to Bloom
Unlike most other species of viburnum, the Chinese snowball blooms are both sterile (meaning they do not produce fruit) and fragrance-free. These large blooms make popular cut flowers and make a particular stunning arrangement when several flowers are cut and arranged in a tall vase.
Failure to bloom is sometimes traced to poorly timed pruning. Ideally, these shrubs should be pruned immediately after they flower. Early spring pruning can remove the flower buds for the current season, but the shrub will return to a normal pattern the following year.A hard rejuvenation pruning will often stimulate intense flowering, though there will be a delay in seeing these results. The first spring after such pruning will see much-reduced flowering, but the following spring will produce a magnificent display.While it’s typical to fertilize these shrubs after they flower, you may want to add an early spring feeding with balanced fertilizer if your shrub is not flowering fully.If surrounding trees have grown up to shade your shrub, the shade might be hindering flower production. Good pruning of surrounding trees might improve the exposure and return your shrub to profuse blooming.
Common Problems With Chinese Snowball Viburnum
These are very hardy, easy-to-grow shrubs, but you can encounter a few issues.
Shrub Is Overgrown and Sparse
In the right conditions, these can be surprisingly large shrubs. If a Chinese snowball viburnum is overwhelming its space, perform a hard rejuvenation pruning in late winter. You’ll be rewarded with a denser, more compact shrub that flowers intensely within a year. Such hard pruning should be performed every few years. Leggy sparseness is sometimes the result of a plant growing in too much shade. Pruning surrounding trees to provide your Chinese snowball viburnum with more sunlight may help it become fuller.
Leaves Are Shriveling, Branches Are Dying Back
While many shrubs are fairly tolerant of drought once they are established, Chinese snowball viburnum needs consistent, regular watering—at least 1 inch per week through combined rainfall or irrigation. Even a few weeks of no water can cause dieback to begin.
Leaves Are Covered With Whitish Powder
This is powdery mildew, a very common soil-borne fungal disease that affects many shrubs. In some climates (warm, humid conditions) powdery mildew is unavoidable and gardeners learn to tolerate it because it is almost never fatal. Ground-level soaking rather than overhead watering will help prevent the disease from spreading because this keeps the spores from splashing up onto the leaves. If the appearance of powdery mildew is unacceptable to you, spraying with fungicides can be used early in the season to prevent the disease from taking hold.
