Hedge your bets at pruning time
By Adrian Higgins,
If you are itching to get into the garden on a mild winter’s day, you might want to grab a good pair of hand pruners and some sharp loppers and go in search of a shrub to prune.
This is an adventure fraught with peril for the shrubs, but if you have a reasonable sense of what to do, you can improve the look, health and vigor of these garden stalwarts while bringing them under control.
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.
I don’t know that I would have a large old lilac in a Washington garden; it is simply not ornamental enough outside its week or two of bloom. But the standard pruning regimen is to remove about a quarter of its oldest branches and suckers each year, but do this in early May, when you should also take off the faded flowers before they form seed.
Now is the time to attack the roses. The high-performing landscape roses don’t need the delicate pruning that attends hybrid teas and grandifloras — they can be chopped back with hedge shears and will shoot back and bloom. But in our subtropical climate, it just seems right to devote the same care to pruning a workhorse like Knock Out as you might something more delicate and prone to the dreaded blackspot. You must have thick, thornproof gloves for this job. My initial prune is with the loppers, cutting the bush back and removing old and sick canes entirely. Ideally, you want half a dozen or so healthy canes forming a bowl around the crown. Use the hand pruners to cut them down to about 20 inches or so, cutting them half an inch above an outward facing bud. All this will promote an open and healthy habit come May. Make sure you pick up all of last year’s leaves, which harbor blackspot spores.
The common bigleaf hydrangea should be left alone, no matter how twiggy it looks. After the new shoots have emerged in April, you can trim around them by removing dead or congested stems. The summer-flowering Hydrangea paniculata benefits from a little pruning now: Take out the oldest stems at their base and trim back the stems bearing last year’s dried flowers.
If you are unnerved at the prospect of pruning, just tackle the butterfly bush. Use the loppers to cut it back to about 12 inches above the ground. Even if you can’t see any buds, new growth will emerge in April. Four to six weeks later, I cut the fresh stems back by about a half. This promotes bushiness and a long season of bloom, a season that starts in just three weeks if spring is your marker.
Read past columns by Higgins.