How can I prune viburnum?
There are a large number of viburnum species and varieties. In general they require very little pruning. Two reasons why you might want to prune viburnums are first, to shape the shrub and second, to revive an overgrown specimen. The exact procedure used will depend partly on why you are pruning and also on the species or variety of viburnum.
All viburnums flower on old wood, i.e. the flower buds are formed in the previous year. Therefore, pruning too late in the year will result in the loss of next year's flowers. To shape a viburnum, prune it lightly immediately after flowering. Remove the flower heads and cut back any branches that spoil the shape of the shrub to a pair of newly-sprouted leaves.Remember that removing the flower heads will preclude the formation of fruit, which can be very attractive in many viburnums.
More extensive pruning should be left until late winter and early spring. Rather than cutting back the whole shrub, it is preferable to prune back about a third of the branches each year. Branches can be cut back to within a few inches of the ground. At the same time, remove any dead or damaged branches. For winter flowering viburnums (e.g. Viburnum x bodnantense and V. farreri), this type of pruning should be done immediately after flowering. Finally, any suckers that appear during the growing season should be removed.
Courtesy of the NYBG Plant Information Service