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Make the Right Cut When Pruning Trees
by Jonathan Heaton - January 2013

The thought of pruning a tree can be intimidating. It is much easier to cut a branch off than it is to put it back. Once you have an understanding of some basic pruning techniques, it is not as hard as it seems.

Practice patience and restraint. Keep the big picture and overall goal in mind, but don't get overwhelmed. Start in a small portion of the canopy, take out a few branches, then step back to take in the big picture before you cut more. Take your time and learn how much to cut, how to cut it and what to cut. 

How Much to Cut

Removing branches from a tree reduces the amount of energy it is able to produce each day. The tree needs to use energy to heal the wound as well as nourish itself. Excessive pruning can easily cause stress for the tree and lead to negative consequences.

For example, over-pruned trees tend to grow prolific water sprouts along the branches in response to the stress. The sprouts will need to be pruned more frequently and are weaker than normal limbs. A general guideline is to remove no more than 25 percent of the canopy, or leaves, to avoid excess stress. However, when practical, I prefer to take less and prune more often to minimize stress. 


Several years after the flush cut was made the bottom of the wound is not healing over nearly as quickly as the rest of the cut. The end result will be increased decay in the trunk.

How to Cut

It is helpful to know a little bit about how woody plants deal with wounds when tackling pruning tasks. The outer layers of the trunk and branches are alive. They grow new wood and bark as well as transport water and nutrients throughout the tree. The inner layers are essentially dead, but they are important for the strength of the tree. Just like a piece of untreated lumber, dead wood will rot or decay when exposed to the elements. This causes the tree to become structurally weaker.

Trees have natural tools to stop, or limit, the spread of decay with a process called compartmentalization. Internally, the tree will undergo chemical and physiological changes to stop decay. Externally the tree grows around the wound, closing it off from the elements. The goal when pruning is to avoid interfering with these processes so the tree can heal, stop decay and stay strong. 

Look for the Branch Collar

There is an area at the base of most branches that has specialized cells that grow relatively quickly around the wound. This is usually indicated by the branch bark ridge and the branch collar. The branch bark ridge is a raised strip that forms in the middle of a branch union. The branch collar is a swollen area at the base of the branch.

A common mistake is to make a flush cut flat against the limb you are removing the branch from. This cuts into the specialized area in the branch collar and the wound then takes longer to heal. Make the cut just outside of the branch collar and bark ridge. In cases where they are not visible, you can estimate where to make the cut based on where a typical branch collar would be.

These photos show close-up views of branch unions. The edited versions point to the collar and the bark ridge. They have lines to indicate 1: the proper cut. 2: the improper placement of a cut, or a flush cut.

Three-Cut Method

Another common mistake is to make one cut when removing a branch. The branch starts to fall before the cut has been completed and rips the bark below the branch collar creating a large wound. Instead of making one cut from the top use the three-cut method. Start with a cut on the bottom side of the branch a few inches out from where you want to make the final cut. This will prevent the bark from ripping. Next make a cut on top of the branch a few inches out from the bottom cut. The second cut will remove the branch and leave a stub behind. Make the third cut to remove the stub just outside the branch collar.

When making a reduction cut — to shorten the length of a branch rather than remove it completely — there will not be a branch collar. In this case make the cut close to a smaller branch coming off of the branch you want to reduce. The smaller branch should be at least one-third of the diameter of the cut branch in order to sustain the life of the limb. If you want to make a cut where there is no smaller branch, such as when the limb needs to be trimmed a small amount, try to make the cut close to a new bud. 


The first cut is done on the bottom to prevent the bark from ripping down into the collar.

The second cut will remove the branch leaving a stub.
 

The final cut is made at the branch collar.
 

What to Cut

Ultimately, what to cut depends on your overall goal. Are you trying to improve a tree’s health and structure? Maybe you need to allow more space for your house or mowing the lawn. Usually you will have multiple goals, which can make it difficult to keep from removing more than 25 percent. Remember that you can prune the tree again in the future, so you don't have to take care of it all at one time.   

Start with removing branches that are dead or broken. These do not count toward the 25 percent limit. Then prune for clearance to your house, over the lawn, sidewalk, driveway or other areas where the tree is an obstruction. Be sure to give 12 to 14 feet of clearance over a road to avoid damage from large trucks.

Next, work on thinning and reduction to improve the structure of the tree and reduce the risk of branches breaking during storms. Thinning is selectively removing branches in the canopy to reduce weight and wind resistance, to improve light penetration or to prevent potential health problems. Reduction is shortening a limb without removing it entirely, such as when you want to trim the tree back from your house. Reduction can be used to take weight off of the end of a limb or to provide more light to areas that a tree has grown over.

Branches that are weakly attached should be removed, if they are small, or reduced, if they are more than 3 to 4 inches thick. Remove branches that are rubbing to provide better spacing. Make sure to remove branches in an even way, so that not all of the pruning is done on one side.

Removing branches closer to the outside of the canopy will net greater benefits when you are trying to get more light through the tree or reduce the risk of storm damage.

When making reduction cuts for clearance, select a smaller branch or bud that is growing away from the house, road or other area to lessen the need for pruning in the future.

A Final Word on Safety

Last year I visited my parents in Utah to find that a 20-foot tall maple (Acer spp.) in their front yard was declining due to girdling roots. The best course of action was to remove the maple and start over with something else. I didn't have time to help on that trip, so I suggested they call a tree service.

My dad, being the thrifty man that he is, decided to take down the tree himself with a chainsaw and ladder. When he removed a large branch from the top of the tree, it swung and knocked the ladder out from under him. He was extremely lucky to walk away with nothing more than painful bruise.

If you have pruning that cannot be done standing on solid ground, I recommend calling a professional. It requires special skill and equipment to work off the ground. Safety should be your first priority. The money you may save by doing it yourself is not worth the risk. To find a certified arborist, visit the International Society of Arboriculture, treesaregood.org.

Photos by Jonathon Heaton.

 


Jonathan Heaton is an ISA certified arborist working for Bartlett Tree Experts in St. Paul, Minn. He can be reached at jheaton@bartlett.com or follow him on twitter @mnarborist.

 

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COMMENTS

TreeGuysTalkingTrees - 04/15/2019

The image about the branch collar and branch bark ridge is incorrect. The bark ridge is on the top and the collar is the tension wood (tapered) wood on the bottom of the branch.
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