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Continued: Guide to pruning

  • Article by: JEFF GILLMAN , Contributing Writer
  • Last update: March 9, 2010 - 4:36 PM

The coldest part of winter has passed, but we have a while before the buds on most trees and shrubs start popping. Though it might seem like a dull time of year, it's one of the busiest if you do your own pruning. Late winter and very early spring are the best times to prune most trees and shrubs. But before you start whacking, there are some things that you should know.

Essential equipment

Anyone with pruning aspirations needs a pair of bypass pruners. This kind of pruner has two blades that slide by each other, just like a pair of scissors. (Anvil pruners, in which one blade cuts onto a flat surface, aren't recommended for pruning because they can crush the bark.) In addition to pruners, you'll need a good pruning saw to remove larger branches.

It's wise to sterilize your equipment with rubbing alcohol after pruning each tree or shrub, to prevent transmitting any diseases from plant to plant. Bleach, which was once widely used in pruning, is no longer the sterilizer of choice because it can be poisonous to plants.

Which plants to prune

Almost all trees and shrubs can be pruned during the late winter and early spring. But don't wait until the buds start to open. Pruning becomes risky then because the weather will be warmer, which means there will be more plant diseases present that can infect a fresh wound.

If you prune spring-blooming shrubs (such as forsythia and lilacs) at this time of year, you will remove some flower buds, making for a less showy appearance later in the season. But I'd rather have a shrub with fewer flowers than one more likely to be infected with a disease.

Pruning large trees is a job best left to a professional arborist. (To find a certified arborist, go to www.isa-msa.org/.) It can be downright dangerous to climb around with pruners and a saw. So if you're tempted to get out a ladder, get out a phone book and call a pro instead.

What you should remove

There are lots of methods for training trees and shrubs, but the basics remain the same. When you prune, you should remove branches that are:

Dead or dying. Go for them first. If left for too long, dead branches can cause problems for the rest of the tree.

Suckers. Those sprouts that occur near the base of a tree or shrub detract from the look of the plant.

Crossing or growing downward. Crossed or dangling limbs can rub against each other, which can cause damage to the bark, which in turn makes for an easy entry point for insects and diseases. Limbs that grow downward will need to be removed eventually. The sooner the better.

Competing leaders. Young trees need a single, central limb to guide their growth. If two or three top limbs are the same height, the tree will grow with poor form, so it's best to remove all but one of these branches.

Narrow crotch angles. When two limbs are growing at so tight an angle that they are pressing against each other, one of the limbs needs to be removed. Otherwise, the limbs will eventually develop a poor attachment to the stem and be susceptible to being broken off in heavy winds.

The kindest cut

Once you decide which limbs need to be removed, it's important to make the best cut you can.

The old standard for pruning called for making cuts flush with the stem of the tree. We've learned that flush cuts are more damaging to trees than cuts that are made at the branch collar.

A branch collar is the area of the branch right next to the stem that is a little thicker than the branch itself. Look for the branch collar 1/8 to 1/2 of an inch beyond where the branch intersects the stem. Cuts made at the end of the branch collar will leave a smaller scar on the tree and heal faster.

Despite all of the tars and shellacs available to coat pruning wounds, there is no evidence that coating a pruning wound will speed the healing process. There is even some evidence that these substances actually inhibit wound closing.

Prune with patience

With a little practice, it's not hard to become proficient at pruning. Remember to start slowly, think before you cut and keep your eye on your trees and shrubs as they take shape over the years.

Jeff Gillman is an associate professor of horticulture at the University of Minnesota. He's also the author of three books, "How Trees Die," "The Truth About Garden Remedies" and "The Truth About Organic Gardening" (Timber Press, $12.95).

Watch a how-to video on pruning at www.startribune.com/homegarden.
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