Prune Like a Pro

Cass Turnbull

Pruning a tree or shrub incor­rectly can make the plant less at­tractive and endanger its health. In the case of trees, poor pruning can even endanger your safety by weaken­ing the tree. Yet many home owners arid professional gardeners don't prune properly.

Most trees and shrubs are hearty enough to recover from pruning mis­takes, though it might take years. Seven of the most common mistakes...

MISTAKE 1: Tree topping. Some home owners believe they can control the height of trees by lopping off the tops, but height is largely under genetic control, preordained from the time the tree takes root. Cutting off the top will only compromise the tree's appearance, health and safety. After a tree is topped, decay can enter the major limbs. Simul­taneously, the tree speeds up its growth rate to compensate for lost foliage, ex­pending energy and weakening the tree. The new branches that result tend to be weakly attached, making them a hazard later, when they are large and heavy. The exceptions are fruit trees, such as apple, pear and peach trees-the height of these can be controlled by topping.

Better: If a tree is too tall for its location, the only remedy is to cut it down and plant one that won't grow as high -although you can make a tree less imposing by trimming the leafy canopy or removing some lower limbs.

MISTAKE 2: Cutting branches flush to a tree trunk. If you cut branches flush to the trunk-or flush to an in­tersecting branch-decay penetrates the trunk, reducing the life span of your tree. Leaving a longish stub of the branch is just as bad, because decay and insects will be able to get in once the stub rots. Applying pruning paint won't solve the problem-research has shown that these coatings are worthless.

Better: Remove a tree limb by cutting  close to the trunk or parent stem, but not flush to it. Leave the collar in place - the turtleneck-like bulge at the base of the branch.

MISTAKE 3: Pruning every shrub into a tidy round or rectangular shape. A neat shrub might appeal to you, but it's bad for many shrubs, including conifers (such as junipers), deciduous flowering shrubs (spirea) and broadleaf evergreens (rhododendrons). Shearing off branches creates a dense, twiggy shell-like exterior that restricts the amount of light reach­ing leaves and keeps air from circulating inside the plant-problems for shrub health. It also forces shrubs to waste energy by regrowing branches you've cut. The replacement branches are like­ly to be unattractive water sprouts (see "Trimming water sprouts").

Better: Prune selectively, trimming branches here and there for a tidier, more elegant look. If you prefer a tightly trimmed look, use the right plants, specifically those with small leaves, such as yew, boxwood, privet, pyracantha, box honeysuckle, Japa­nese holly and bougainvillea, which are hearty enough to stand up to pruning.

MISTAKE 4: Trimming water sprouts. Pruned plants sometimes develop water sprouts-ugly, twiggy upward growths from spots where branches were cut. Cherry and crab-apple trees, magno­lias, witch hazel, double-file viburnum and purple-leafed plum are prone to water sprouts. Most people remove these growths, only to find more appearing in their place the next growing season.

     Better: Water sprouts should be considered a sign that the plant has been overpruned and needs more branches. When water sprouts appear, the best option often is to allow them to grow and prune the plant less in future years.  

MISTAKE 5: Using hedge clippers. These clippers trim the surface of a plant, which is appropriate only for hedges. Power hedge clippers, in par­ticular, should be used only on hedges because they can do a lot of damage.

Better: Most trees and shrubs should be pruned so the cuts are hidden inside the plant, where the branches fork off from other branches or the trunk. Prun­ing tools include bypass hand pruners and a pruning saw. Felco- 2 bypass hand pruners (cost: $70) and the Felco-600 folding pruning saw (cost: $31) are con­sidered the industry standards. Available from Amazon.com and gardening stores. www.felcousa.com.

MISTAKE 6: Cutting off branches that are too large. If the diameter of a branch is more than half the diameter of the tree's or shrub's trunk or stem, it is too large to be removed without sig­nificant risk to the health of the plant. The plant will be unable to wall off the injury, and decay will gain access.

Better: Don't wait until a branch rubs against your roof or blocks your driveway before cutting it off. If the branch is anywhere close to half the diameter of the trunk or stem, remove it now before it grows any larger.

MISTAKE 7: Heavy pruning dur­ing seasons of harsh weather. Heavy pruning can put a lot of stress on a plant, as can the heat of summer and the freezing cold of winter.

Better: Do major pruning during times of the year when temperature extremes are unlikely in your region so that these combined stresses don't overwhelm the plant. Spring is usu­ally the best time for heavy pruning. (Moderate selective pruning is okay anytime of year.) Generally, it's best to prune flowering trees and shrubs soon after they flower.