How and when to prune a shrub depends on what it is. The golden rule: Better to do no pruning than to butcher the wrong shrub. (Though some shrubs love to be butchered.) You might say, well I’ll just get the landscapers to clean up the bushes when they lay the mulch in March. This assumes that they know what they’re doing, which isn’t always the case even if they plead competence. A sign of trouble: arbitrary snipping with no regard to branch structure or buds. Another red flag: a “landscaper” giving a shrub a crew cut.
Shrubs that bloom in the spring — azaleas, pieris, viburnums, for example — set their flower buds late last summer, so hacking them back now will cost you blooms. Summer and fall bloomers such as crape myrtles, butterfly bushes and rose of Sharon flower off entirely new growth, so they can be pruned in winter dormancy without loss.
I lump small deciduous trees in with shrubs for winter pruning — they benefit from the removal of rubbing, dead or inward growing branches as well as old improperly pruned stubs. This remedial and inherently conservative pruning also applies to spring bloomers such as cherry trees, dogwoods, redbuds and apples. Whatever flowering wood you might remove is worth it for the beauty and health of the tree, and winter is the time to see the structure. Weeping Japanese maples require a particularly deft and artistic touch. They also bleed — perhaps that’s one specimen to leave alone.
Generally, though, anytime you can bring light and air into the heart of a small tree or shrub, the better. It improves flower production and reduces the chance of fungal disease. Florally, forsythia is a flash in the pan. The roots of an old, tatty hedge are impossible to grub out once established, but forsythia does benefit every few years from a hard cutback. Wait until mid-April, after blooming. The same principles apply to its mounded doppelganger, the winter jasmine. I cut mine back hard every three years, also in April. The flower display might be diminished the first winter after that, but not by much. If I had a chain saw, I would take that to the thicket of jasmine and leave stubs no more than 12 inches high.
You can do the same now to beautyberry, which can get extraordinarily big if left unpruned over several years, as much as eight to 10 feet. When I had beautyberries, I would take the loppers to them in late winter and they would look stubby and mutilated when I had finished. But within a few weeks of spring growth, they would form well-behaved mounds, three feet by three feet, and end the season covered in their decorative fruit.
Rather than chop back that other amiable, late-season weed, the rose of Sharon, remove the older (thicker, darker) stems at their base, and lighten the remaining branch structure through artful deletion. Again, start with the removal of inward growing and rubbing branches.