Snowball bush (Viburnum spp.) produces its signature large, brilliant white flower clusters in late spring. Pruning the bush at the wrong time may jeopardize the abundance of those showy flowers, so it's important to prune just after the flowers fade in late spring or early summer.
Snowball Bush Species
Three species have the common name snowball bush. They differ size, blooming habit and cold hardiness:
- European snowball bush (Viburnum opulus 'Roseum') is the largest of the species. It grows in U.S. Department of Agriculture plant hardiness zones 3 through 8. It usually blooms in May.
- Chinese snowball bush (Viburnum macrocephalum) is the smallest of the three species, and it is also the least cold tolerant. It grows in USDA zones 6 through 9. It generally blooms in May or June.
- Japanese snowball bush (Viburnum plicatum) grows in USDA zones 5 through 8. It usually blooms in May.
Snowball bush produces new flower buds in summer that will bloom the following season, so the best time to prune the bush is just after the current season's flowering ends, typically in May or June, depending on the flowering time for your specific variety. This allows the plant plenty of time to produce new growth and develop new buds before the end of the growing season.
Pruning later in the summer may remove the new buds after they've begun to develop, and the bush won't have time to recover before fall. Pruning early in spring risks removing the current season's buds before they bloom.
Pruning every year or two will help to shape the bush and keep it from getting too large. Prune away as much as one-third of the length of the branches to control the plant's size.
If the bush is overgrown to the point that light pruning of its outer branches isn't enough to get it under control, thin out the center of the plant by pruning interior branches down to the ground before reducing the length of outer branches.
You can rejuvenate a struggling bush by pruning it severely every few years to about 2 to 3 feet tall. This type of severe pruning is likely to mean you get few or no flowers the next season.
To prevent the spread of diseases and pests, sterilize your pruning tools by dipping them in 70 percent isopropyl alcohol between each cut. When moving from bush to bush, soak the pruners in alcohol for two to five minutes between bushes.