Pruning trees, shrubs with care, purpose

Photo shows two crape myrtles of the same variety and same age. The one on the left was severely pruned the previous spring while the tree on the right was left untouched.

I once had a neighbor that would chop back a red maple from time to time. One day, the tree form would be full and the next it was a 10-foot-tall hat rack. He didn’t really have a reason. He said the tree just needed it. When the foliage grew back, it looked less like a maple and more like something Dr. Seuss would invent.

The problem, as I once tried to explain, was that incorrect pruning leads to weak branching structure and subsequent decay. Pruning isn’t always necessary.

Unless plants are crowded or branching needs correcting, trees can be left alone. That goes for crape myrtles, by the way.

Ideally, good landscape design allows space for trees and shrubs to grow unimpeded. From time to time, however, pruning is needed.

Technically, you can prune any time of the year. You won’t kill a plant by pruning it at the wrong time, but you could cause undue stress and affect flowering.

Many experts believe winter is the best time to prune. Branching structure is easier to examine once the leaves have fallen and damaged branches are easier to identify and correct.

Pruning cuts also will bleed much less sap in the winter.

The least desirable time to prune is shortly after new growth has emerged in spring. Healthy plants will tolerate pruning at this time, but you’re causing stress by removing new foliage.

You’ll also get excess bleeding that stains the trunk. While this isn’t harmful, it is unsightly.

Late fall also is a less-than-desirable time to prune since it can stimulate new growth at a time when the plant is hardening off for winter. Again, healthy plants are tolerant, but wait if you can.

Trees and shrubs will either produce flowers on last year’s growth or the current season’s growth.

There are some plants that produce flowers on both old and new growth, such as Encore azaleas and Endless Summer hydrangeas, but most trees and shrubs are one or the other.

For instance, the flower buds that will bloom on azaleas this April were set last summer.

If you prune an azalea now, you’ll remove most of the flower buds. The blooms will be spotty at best. Trees and shrubs of this nature typically set the following year’s flower buds in July.

Crape myrtles are the best example of a plant that flowers on the current season’s growth.

In fact, I believe the practice of severely pruning crape myrtles into submission was an attempt to force more new growth for more flowers. Clemson, however, has shown that correctly pruned crape myrtles flower more profusely (www.clemson.edu/crapemyrtle).

If you don’t know when your tree or shrub sets flower buds, play it safe and prune right after it flowers.

Always prune a branch back to another branch. Think of the letter Y.

Prune the left line back to where the two lines split, so it now looks like a single line going up and angling to the right.

Random pruning results in numerous weak branches called water sprouts that disrupt the tree’s natural form. The evidence, unfortunately, appears on too many crape myrtles.

If you grunt trying to make the cut, your pruners are likely too small. Hand pruners are for branches less than half an inch. Long-handled loppers typically cut branches up to 1 inch, although some designs cut up to 2 inches.

Pruning saws are often curved and cut large limbs on the backstroke. Folding pruning saws are convenient and very aggressive.

While the chainsaw makes the roughest pruning cut, it does a lot of work. It’s also very dangerous, so operate with care. Gas-powered chain saws are preferred, but electric chainsaws are frequently suitable for many homeowners.

A proper pruning cut will seal over with callus tissue over time. There’s no need to paint pruning cuts.

Tony Bertauski is a horticulture instructor at Trident Technical College. To give feedback, email him at tony.bertauski@tridenttech.edu.