The snowball bush, a cherished, old fashioned garden shrub that produces fluffy balls of summery white blooms, is a member of the Viburnum genus. Growing to a height and spread of up to 10 feet or more, the snowball bush may be planted as hedge, privacy screen or focal shrub. Although most viburnums with true, full globe shaped florets do not produce fruit, they do offer pretty autumn foliage and bright red, bare canes during the colder months. Pruning at the right time with proper techniques is important for maintaining the shape and health of your snowball bush.
Prune viburnum bushes in the spring as soon as the last flowers fade. Snowball bushes bloom on old wood or last season's growth. Pruning any time past late summer will risk removing precious bloom buds.
Prepare by gathering tools. Dilute 1 part bleach to 4 parts water in a clean bucket for dipping tools that may come into contact with diseased plant material. Have trash bags ready to contain potentially infected foliage. Disease can spread through plant material that falls into other bushes, in a compost pile or from dirty tools to other plants.
Start by Thinning Pruning, which creates a nicer overall shape and provides better air circulation and space for the center of the shrub. Cut back longer branches on old growth to the main branch, or older branches clear to the ground. Allow at least one-half inch margin between the cut and the main branch to avoid wounding the base branch.
Encourage new growth and a fuller canopy by Heading Back pruning. Remove selected branches by cutting just above the node of a bud, identified by a set of leaves, at a 45-degree angle with the base of the cut one-quarter inch above the bud. Heading cuts should be done sparingly and at varying heights, keeping in mind the overall desired shape, to avoid an overly bushy canopy.
Restore an old, overgrown viburnum that is no longer flowering well by Renewal Pruning. Clemson University Cooperative Extension horticulture experts suggest that this process should be completed in the spring. Cut back all branches to within a foot of ground level. Although you will sacrifice blooms for that year, a healthier, happier snowball bush should emerge the following season. If you cannot bear to part with all the blooms for the entire season, consider splitting the renewal pruning over three years, removing one-third of the old canes each year.
Clean your tools during the pruning process if disease is suspected or confirmed. Dip the metal parts of tools into the prepared bleach mixture in between each cut as well as after pruning is complete. Thoroughly sanitize tool handles, wheelbarrows and other equipment that may have come into contact with sick foliage. Use hand sanitizer to prevent becoming a carrier, accidentally spreading illness in your garden.