Planted 4 years ago, our kor sp Viburnum are now at least 6 feet tall and bloom nicely, except for the very top (last foot or so of growth). Do we need to deadhead spent blooms? When? Do we need to trim the tops? Is other pruning required?
Nearly all viburnums bloom on one year old wood. Pruning late in the summer eliminates the flower buds for the the spring of the following year. any pruning should be done shortly after bloom show each year. If your flowers are not being pollinated and have no seed (good for birds), you can deadhead if you wish. Normally any new vegetative growth following bloom covers up the spent flowers.