Viburnum shrubs are known for their attractive flowers, foliage, and sometimes berries. Successfully cultivating these plants to produce abundant blooms depends on understanding their specific flowering habits. With over 150 different species, the necessary pruning schedule is determined by the type of wood on which the flower buds form. Incorrect timing can easily remove an entire season’s worth of flowers, making it important to identify your shrub’s bloom cycle before making any cuts.
Timing for Viburnums that Bloom on Old Wood
Most commonly planted Viburnum varieties, such as Koreanspice (V. carlesii) and Doublefile (V. plicatum), set their flower buds on wood grown during the previous season. This pattern is known as blooming on “old wood,” meaning the reproductive structures are present and dormant throughout the winter. These shrubs typically flower early in the spring before the plant has fully leafed out, utilizing stored energy from the prior year’s growth.
The perfect window for pruning these varieties is immediately after the flowers fade. Once the petals drop, the plant begins setting the new buds for the next year’s bloom. Pruning at this time allows the shrub to recover quickly and gives the new growth an entire season to mature and form the following year’s flower buds.
Delaying the pruning until late summer, fall, or winter will result in the direct removal of the flower buds. This mistake will not damage the overall health of the shrub, but it will eliminate the spring bloom entirely. For the best floral display, all shaping and size reduction must be completed within a few weeks of the current year’s bloom completion.
Timing for Viburnums that Bloom on New Wood
A smaller number of Viburnum species flower on “new wood,” meaning their bloom buds develop on growth produced during the current season. These varieties generally bloom later, sometimes extending their flowering period into the summer months. This growth habit requires an opposite approach to pruning compared to their old wood relatives.
New wood bloomers should be pruned during the dormant season, in late winter or early spring before new growth begins. Pruning at this time encourages the plant to produce a robust flush of new stems once the weather warms. This vigorous new growth will subsequently generate the flower buds and produce the summer blooms.
This late winter timing allows for more aggressive size reduction or shaping without sacrificing the upcoming flowers. By removing older material before the spring growth starts, the shrub redirects its energy into fresh stems that will be highly floriferous later in the season.
Essential Pruning Techniques and Goals
Viburnums rarely need extensive cutting, and most pruning is done to maintain shape or health. Pruning techniques should be applied to achieve specific goals based on the shrub’s condition.
Rejuvenation or thinning is a common goal. This technique involves selectively removing the thickest, oldest canes by cutting them back entirely to the ground. Removing approximately one-third of the oldest stems every two to three years helps to open the shrub’s center to light and air, promoting healthy new growth from the base.
For routine maintenance and size control, cuts should be made just above a lateral branch or a healthy outward-facing bud. Making cuts at these specific points, known as heading cuts, directs the plant’s energy to produce new growth in the desired direction, maintaining a more compact shape. This method prevents the shrub from becoming leggy or too tall for its location.
The removal of dead, damaged, or diseased wood must be performed at any time of year, regardless of the flowering cycle. This process, often called sanitation pruning, involves cutting the affected branch back to a point of healthy wood or to its point of origin. Removing them immediately prevents the spread of potential pathogens and improves the overall appearance of the shrub.