- 1). Prune away any dead, damaged or diseased twigs and branches. Dead and diseased tissue can be removed at any time of the year, but trimming broken branches is best done in spring or summer to allow new growth to mature well before fall. Make the pruning cuts with hand pruners, 1/4 to 1/2 inch above a lower branch junction, leaf or dormant bud.
- 2). Look at the overall shape of the snowball viburnum. You may wish to trim errant, irregular branches. Also look for branches that are encroaching upon a building facade or other shrub. According to Erv Evans of North Carolina State University, viburnum shrubs typically need pruning about every five or six years.
- 3). Trim back branches or twigs, a process known as "thinning," as needed, using the pruners. Make pruning cuts 1/4 to 1/2 inch above a pair of leaves, a dormant bud or a junction with a lower living branch. Overall, use restraint since trimming is designed to preserve the shrub's natural form, not butcher it into a formal, geometric shape. Often, reducing the length of a twig no more than 6 inches rectifies the situation.
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