Prudent pruning

Go ahead and give 'em a trim. Tree trimming done correctly promotes good branch structure and improves the overall health of the tree by removing dead, diseased, and dying branches, says Rick Reisinger, farm manager of the research orchards at Cornell University. Thinning the crown also permits new growth and better air circulation.

"Regular pruning can extend the life of a tree by keeping new wood and foliage growing all the time," says Reisinger. "Not pruning could cut the life of a tree in half."

But before you start sharpening your shears, consider the following guidelines.

When to prune

Routine pruning to remove weak, diseased, or dead branches can and should take place any time. Otherwise a good rule of thumb for most trees is during a dormant period (late fall and winter) when sap loss is minimized and there is less stress to the tree. There is also lower risk of fungus infection and insect infestation because these threats tend to be dormant during this time as well.

One exception: flowering trees like cherry, peach, and plum varieties (the stone fruits) are best pruned near bloom time. "Their wounds heal more quickly during warm, dry periods," says Reisinger.

How much to prune

Remember that all prunes place some stress on a tree, so cut as little as possible. And never prune more than 25% of the crown.

Making the cut

Cuts should be made just outside the branch collar, located at the base of the limb. Since the branch collar contains important trunk or parent branch tissue, it should not be damaged or removed. Never make cuts flush to the trunk because that removes the protective chemical zone and exposes the tree to infection.

Larger limbs may require a three-cut method to reduce their weight and prevent tearing the bark. Make an undercut about 12 to 18 inches from the limb's point of attachment and make a second cut from the top directly above or a few inches further out on the limb. Remove the limb, leaving the 12- to 18-inch stub, and then remove the stub cutting back to the branch collar.

Dealing with storm damage

After a storm, inspect your trees for splits and cracks on the trunk and major limbs. A top priority should be to make the tree safe, which may involve more excessive pruning than usual. "Sometimes you have no choice but to cut way back, and it's often best to take branches broken as a result of storm damage back to their point of origin," advises Reisinger. "Make the cut on a slant to prevent water from building up and causing rotting."

Don't apply tree wound dressing (also called tree paint) to prevent decay-causing infections. Research by the U.S. Forest Service Northeastern Forest Experiment Station shows that not only do tree wound dressings do nothing to prevent disease, but also they may actually serve as a food source for microorganisms.

So when is it time to call in an arborist? According to Reisinger, any time safety is an issue, it's important to bring in a professional. "If power lines are involved or if a tree is very close to your house it's a good idea to let an expert handle the job," he says.

What it will cost

Arborist rates will vary greatly based on the size and difficulty of the job. Look for a tree trimmer with membership in a professional organization such as the International Society of Arboriculture (ISA) or the National Arborist Association (NAA). Be sure and ask for proof of insurance and get references. A poorly trained arborist can do more harm than good.

Pruning tools and personal safety

Basic needs for tree pruning include sturdy gloves, safety goggles, (to prevent eye pokes), and sharpened tools designed for the job. Never use hedge clippers on your trees. It's also a good idea to wear a long-sleeved shirt and long pants to guard against scratches. Most trimming jobs can be accomplished with the following:

Hand pruning shears: Cuts up to 1/2 inch can be made with hand pruners. Select the by-pass variety for clean cuts in green wood; the anvil type for easier cutting of dead wood.

Compound loppers: These work well for cuts larger than 1/2 inch and up to about 2 inches. Select the by-pass variety for clean cuts in green wood; select anvil loppers for higher cutting capacity when cutting dead wood.

21-inch pruning saw: This handy, lightweight, inexpensive tool can handle cuts up to 6 inches in diameter and has a triangular shape that allows it to work in tight quarters. Larger bow saws -- up to 36 inches long -- can cut limbs up to 1 foot thick.

Pole pruners: Two types are available. Manual pole pruners have a lopping blade at the end of a telescoping fiberglass pole, typically about 8 feet long. You position the blade, then pull a rope to cut branches up to about 1 inch thick. Most manual pruners also are equipped with a saw blade, allowing you to cut branches up to about 4 inches thick. Powered pole pruners feature a gas or electric chain saw on the end of a long pole, allowing you to cut limbs up to 1 foot thick and up to 12 feet or so while standing on firm ground.

Chain saws: If you are planning to use a chain saw, heed the advice of tree pruning expert Rick Reisinger, who emphatically says, "Anyone doing chain saw work needs to take a chain saw safety course first! Chaps, hearing protection, good gloves, and safety goggles are all necessities when working with power tools." Experts warn that chain saws should not be used to cut any limb higher than the operator's shoulder height.

To prevent the spread of tree disease from infected tools, soak your implements in bleach water (one part bleach to nine parts water) followed by cleaning with soapy water. Dry tools before storing.