The How & When of Pruning Trees

Question: Should I prune trees in my yard? How and when?

You are right to think about pruning before you act! Pruning trees is generally done to improve shape, strength, and health and to prevent personal and property damage.

Pruning young or mature trees
If you are planting new trees, be sure to understand how large a tree will grow and select one that will be an appropriate size for its placement at maturity – pick the right plant for the right place. Save yourself the time and work!

If you want to prune trees already established in your yard, it is better to start when a tree is younger, but has firmly rooted in your yard. This also requires imagining what the tree will look like many years in the future. Pruning older trees may be necessary to remove dead, diseased or damaged limbs, or to remove a limb that could potentially cause property damage, such as a limb hanging over a roof. For younger trees, do not prune more than 25-30% of the tree; wait to the following year before pruning additional limbs. For older trees, prune 25% or less of the tree. Never prune trees that are near utility lines; ask the utility company to do the pruning. Always prune flowering shrubs and trees after they flower.

Timing
Timing is important so your tree looks good for the next growing season. Virginia Cooperative Extension has an excellent series of publications on pruning including a pruning schedule for deciduous trees.

Techniques
Your first priority is to cut away the dead, diseased, or damaged limbs. Next, remove limbs that are crossing or rubbing against each other.

It is important to leave primary limbs that form the basic shape (scaffold) of the tree. These are the branches that will create the canopy of the tree. Keep the branches that will have the most strength — those having a wider angle between the branch and the main trunk. A branch with only a 30-degree angle or less is more susceptible to future breakage than those with an angle of 60 to 70 degrees.

After selecting a branch to prune, identify the branch collar, which is the swollen tissue joining the branch and the main stem. The branch collar contains callus tissue, which helps heal tissue damage and prevent disease and decay resulting from pruning. To prune small limbs correctly, cut at a slight angle leaving the tree collar intact. Resist the tendency to make a straight, flat cut against the main trunk, which could damage to the tree.

If you are pruning a large limb, use the three-cut method. Make the first cut on the underside of the branch 6-12 inches up from where the branch joins the trunk and saw only ⅓ of the way through the branch. Next, move a few more inches up from the first cut and, starting on top side of the branch, saw all the way through until the branch falls away. Then, cut the branch stump off near the trunk, taking care not to injure the branch collar. The three-cut method prevents tearing of the trunk bark from a limb when it falls. If you need to prune very heavy limbs or limbs high up in a tree, consider contacting a certified arborist to do the job.

Past practice was to coat all tree wounds with tree paint or wound dressing to prevent disease or pests. But this is no longer considered necessary for most trees, except oaks and elms which are particularly susceptible to disease and pests.

References

“Pruning Basics and Tools,” Publication 430-455, Virginia Cooperative Extension.

“Pruning Deciduous Trees,” Publication 430-456, Virginia Cooperative Extension.

“Pruning Evergreen Trees,” Publication 430-457, Virginia Cooperative Extension.

“Pruning Ornamental Trees and Shrubs,” Publication HO-4-W, Purdue Extension.

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