If the bushes in your foundation plantings are overgrown, you may have the urge to start hacking away at them. But before you haphazardly attack that lopsided hydrangea devouring your front walk or the rhododendron obscuring your windows, it's a good idea to familiarize yourself with some of the basic information on pruning shrubs. This brief introduction will point you in the right direction.
How to Begin
Begin by pruning away dead or damaged branches with a pruning shear, lopper, or a saw. Your tools should be sharp enough to leave a straight, clean cut. It's not ideal to leave ragged edges. Consider using anvil pruners and bypass loppers, which allow even smaller hands to cut branches up to one and a half inches thick. You'll need a small powered chainsaw, a wood saw, or metal hacksaw for thicker branches and trunks.
Where to Cut
Prune just above what's known as the "branch collar," that little ring of bumpy tissue at the junction of a branch and main trunk. The bumpy area is rich with plant growth cells. Leaving the collar intact gives your shrub a better chance to callous over and recover from your surgery.
Always cut branches on a slant, at a 45-degree angle. A flat-topped cut may cradle water when it rains, inviting fungus or disease. Rainwater slides off a slanted cut.
For a natural look, use the technique known as "heading back." Eyeball the bush and locate the tallest main branch. With your eye and hand, follow this main branch until it meets a lower side branch that more or less points upwards. Cut the main branch off just above the smaller one. Repeat the process with this and all main branches, stepping back now and then—maybe even across the street—to assess the results. Prune slightly lower down than you feel really comfortable with; remember, new growth will add additional height over the next six months.
For a major overhaul—removing 10 feet or more from a bush—use a saw on the main trunks, removing only a third of the height at each pass to prevent accidents.
Needled evergreens, such as juniper, can be pruned in early spring (although we often "cheat" and take some cuttings for holiday decorations in late autumn or early winter. This is fine, as long as you do not overdo it. After you see the first hints of new growth emerging from your previous cuts, prune again to further reduce the height of evergreen shrubbery.
Needle evergreens are tricky: If you prune below green growth, a branch may never again sprout. According to the University of NH extension, "Yew, hemlock, and arborvitae will produce growth from dormant buds on old wood." But you have to take it easier with many other types, including "juniper, spruce, pine, and fir," which "usually do not form buds on old wood."
Some Deciduous Examples
Rejuvenate fan-shaped (or "vase-shaped") deciduous bushes such as forsythia, lilacs and bush-form roses by cutting back a third of all branches right down to the ground each year. If part of the value of a shrub is the gracefulness of its natural form, be careful not to spoil it by getting carried away with your pruning. Forsythia is perhaps the poster child for this warning. It ultimately wants to grow into a vase shape—and you should go out of your way to oblige it.
For bushes in foundation plantings, prune away any branches rubbing against the house or wall. Your neighbors won't see the plant's backside, so feel free to cut back for up to 12 inches of clearance. This improves air circulation around the back branches and ultimately results in a healthier bush.
When to Prune
Do you need to cover the cuts with tree paint or wax? No. If you have made a good, angled cut at the proper time, each species will safely heal its wounds without damage from frost, insects or disease.
The proper time to prune needled evergreens such as pines is the winter dormant period. Flowering shrubs are trickier because trimming them at the incorrect time can mean a loss of next year's flowers. The rule of thumb is that if the bush blooms in fall or in late summer, you should prune it in early spring before new growth emerges. By contrast, if the plant flowers in spring or in early summer, wait till after it has completed its flowering, then proceed with pruning.