When and how do I prune my overgrown viburnums?
With Viburnum pruning, less is more. Please don’t think of my favorite genus of shrubs(and great bird plants, too) as hedge material to shear and mutilate. The protocol:
Usually viburnums need relatively little pruning, assuming you planted the right species and cultivar in the right-sized space. Most of the pruning I’ve had to do on viburnums was because I didn’t leave enough room for the plant to reach its eventual size. I have cut several to the ground or thereabouts in very early spring, when they simply got too big, but better space planning is much preferable.
Even the lightest pruning, the removal of spent flowers called deadheading, isn’t needed with most viburnums, since what you want is fruit after the flowers (unlike all that deadheading with lilacs, for instance, to prevent messiness).
If a little fine-tuning or gentle re-shaping is required, I time my cuts right after bloom. That gives the plants time to regrow and potentially set blooms, even, for the following year (depending on how far down I cut on which kind). Cut back judiciously to just above a node with each clip of the shears so the plant can make new shoots in a somewhat natural-looking style. Do not try topping or shearing viburnums halfway!
Of course always look for suspiciously vertical new shoots that jut from the base or up from existing branches and remove.