Of the more than 150 species of viburnum shrubs and trees in the world, the vast majority need little if any pruning in order to develop into perfectly shaped plants for the garden. Making cuts 1/4 inch above a dormant bud or lower branch allows for reducing shrub size as well as maintaining the attractive, natural look.
Proper Plant Selection
Matching your site's size with the expected mature size of a shrub diminishes the need for future pruning. For example, if a garden bed is only 5 feet wide, selecting a species or cultivar that matures to no more than 5 feet in width nearly eradicates any need for shearing, tip pruning or other pruning as the shrub grows and reaches maturity. If a shrub that naturally grows 8 feet wide is planted, expect repeated branch pruning at the potential cost of losing flowers, fruits or a picturesque, naturally shaped plant.
While dead or diseased wood should be removed any time of year when encountered, the University of Georgia's Michael Dirr prefers that pruning of viburnums occur immediately after they flower. This permits you to enjoy the flower display and trim back branch tips to witness them grow during the summer. Flower buds form by late summer, ensuring that the following spring will again provide an attractive flowering display. Avoid pruning in very late summer to mid-autumn, as the resulting new growth may not have sufficient time to mature to survive the first fall frosts.
Extent of Pruning
Dirr further explains in his book, "Viburnums", that "pruning viburnums should be an exercise in restraint." While a hedge of viburnum may seem best tackled with shears, the cutting blades often leave the large leaves with browned edges or irregular, torn leaf blades. Individual and hedge plants look better when only errant branch tips are reduced in length as needed, keeping foliage intact and hiding the pruning cuts. An even, well-distributed tip pruning across an entire viburnum shrub allows a gardener to create the perfectly shaped plant while allowing it grow to its full potential.