Pruning Basics
Fall 2021

Have you had branches from trees or shrubs interfere with your mowing? Do you need to deal with branches shading your garden or crossing over the fence?

This article explains the basics of pruning and how and when to prune safely for you and the tree.

The number one rule of pruning is to use the right tool for the job. An old arborist I learned from many years ago used to say, “Prune when the saw is sharp”. This simple statement speaks truth.

Here are a few myths about pruning trees. Some trees drip sap after pruning. Scientific research has proven that sap dripping after pruning has no effect on tree health. (Refer to figure #1) Another common myth associated with pruning is painting the cuts. Many years ago Dr. Alex Shigo revealed that this practice did nothing to assist the cuts in closing and did not prevent disease infections. One final word on myths. There is no scientific study that proves tree disease can be spread by pruning tools. Therefore, treating pruning equipment between cuts or trees is not recommended by modern arborists.

Modern tree care pruning guidelines focus on dosage and techniques rather than timing and painting. Trees can be harmed by pruning, but normally the harm results when branches are pruned incorrectly using dull and improper tools. Tree stress results when too many branches or too much of the canopy are removed from a tree.

First, select the right tool for the job and be sure that the blades are sharp. Sharp blades make clean and smooth finished cuts. This helps prevent infections from disease after pruning. When pruning diseased limbs, it is recommended to prune in the winter when common tree disease spores are not actively airborne.

Your local STIHL Dealer has a selection of quality sharp bladed pruning tools available, hand pruning tools such as shears, pruners and saws. You will also find an excellent section of smaller specially designed chain saws designed for pruning. A good example is the new battery-powered chain saws. These are an excellent choice for pruning applications.

A rule of thumb, arborist industry guideline or standard, is that no more than 25% of living branches of a tree should be removed by pruning; pruning more than this will cause stress. A tree or shrub that produces a proliferation of young shoots or small branches after pruning indicates stress and that too much was pruned.

The act of pruning can be defined as the removal of branches or sections or parts of branches. This is often referred to as removing limbs to the point of origin or trunk, and also shortening limbs or branches by reducing their length, height or width.

When removing a branch back to the trunk it is important to only prune the branch and not cut the trunk. Trees and shrubs have a natural target that makes it easier to cut only the branch and miss the trunk. Where branches and trunks meet, they interconnect with specialized tissues. This special connection creates a raised or swollen collar and ridges, wrinkles or folds. These formations are known as branch collars and branch bark ridges. The final cut should be made up to but not into these ridges or collars. It is best to stay away from the collar rather than risking cutting into it. These areas make up a tree’s natural protection barrier against infection, and when left intact, it allows the trees to deal with the cuts easily. (Refer to figure #2).

An important step in pruning a branch back to the trunk is to remove the bulk of the weight of the limb before making the final cut. This creates what is known as the three cut method to removing branches. This rule is particularly important as the length and size of the branch increases, such as when you are pruning branches with a chain saw.

The three step technique for removing limbs is shown in the diagram. (Refer to figure #3).

Shortening or reducing a branch has some guidelines also. Branches should be shortened back to another branch so that there is never a stub or blank end left on a branch. The branch can be shortened back to a branch that is large enough, but the branch that is left must be at least 1/3 the size of the branch where it is cut. If there are two branches where you want to shorten the branch to, then select one and remove the other with the shortening cut. Do not leave a 'Y' branch at the end of a shortened branch. This is not a natural formation. The cut should be made on an angle that compliments the angle of the branch being left. (Refer to figure #4).

Pruning cuts that shorten limbs are almost always done with hand tools. If a chain saw is required for a shortening cut, then most likely too much is being removed and stress will result.

Pruning can be dangerous, especially when it involves large limbs and tall trees. When ladders are needed and chain saw size cuts are required, it may be advisable to request an arborist consultation. Use wisdom and safety equipment at all times.

Remember...prune when the saw is sharp, make your cuts correctly and don't cut too much.

By Dwayne Neustaeter Sr., Arboriculture Canada