How to Prune a Tree

It would be impossible to cover this topic thoroughly in a single article, so this is more of a basic crash course on what not to do, some basics on tree response to pruning, and is intended to help you either prune your trees yourself, or make a more educated decision when choosing an arborist or tree service company for pruning your trees. This article does not include palm trees; that topic is covered in How to Prune a Palm Tree. For the rest, please read on.

Tree pruning fundamentals- what’s good for the tree


First, and perhaps most important to understand, is CODIT. This is industry shorthand for Compartmentalization Of Disease In Trees. What is important to know before you cut into a tree is where to make the cut, and how. You see, the placement of the cut can have tremendous impact on the tree’s ability to heal (we should always think of pruning as an intentional wounding, hence the term “tree surgery” or “tree surgeon”). Researchers have been hard at work studying and gaining insights into tree biology, and how trees respond to pruning. What they have learned is quite fascinating, and important to understand before pruning begins. There is a wealth of knowledge that would take multiple college text books to cover completely, so again I will be skimming the surface here. Trees are pruned by man, and by nature. Nature is not very considerate on how it prunes a tree; hopefully your tree service professional is. Every branch on a tree has what is called a branch collar. This collar forms over multiple growing cycles wherein layers of cambium (inner bark) are laid down from the trunk side, then the branch side, then the trunk again, and so on. This build up makes the collar quite strong. It is more obvious on some trees than others, but will show as a larger diameter at the base of a branch where it meets the trunk of the tree. This branch collar, it has been learned, also has active systems in place to stop infection- both fungal and bacterial-from entering the trunk of the tree in the event the branch is removed. This natural defense system does not exist outside of the branch collar. There is a similar collar where a smaller branch joins a larger branch (let’s call that a limb). So the limb has a branch collar at the trunk, and its branches have a similar, but less pronounced, collar where they leave from the limb. These are the places that we make our pruning cuts, because the tree has the best ability to fend off infection while it works on closing the wound with new bark.

The proper place to remove this limb is on the yellow line. The tree will decay if cut on any of the red lines. The bottom red line would be a flush cut. Flush cuts were the norm 20+ years ago, before scientific research showed us that this was the WRONG place to cut off a limb, as the tree was left open to decay.

The one chink in the tree’s armor is dead wood. Dead wood is a natural occurrence- as trees grow in diameter, new tissues are deposited on the outside of the tree, and the heartwood at the center eventually is no longer needed, and dies. When a larger branch or limb is cut, or broken off in a storm, this deadwood is still susceptible to decay- the natural defense system is in the living tissues. Because of this, I always advocate for pruning trees while they are still young and vigorous, the limbs are smaller diameter and can heal faster, and there is less dead wood open to decay. The removal of very large limbs, either by storm damage, impact, or by pruning- can open the tree to decay, and start a long and slow decline of the tree. The good news is that trees that are completely hollow can still stand for decades, so long as the rest of the tree remains healthy. The bad news is that all trees eventually die. Improper pruning can send a tree to an early death. So, we know that it is best in most cases to only prune a branch or limb at its base. Now let’s look at how those cuts should be made.

The 3-cut method of pruning a tree branch

First of all, it is imperative to not split the bark unnecessarily. Splitting will occur if a branch or limb is simply cut from the top down. As the saw reaches the point where there is no longer enough wood to support the weight of the branch, it will fall and tear the bark underneath the branch past the point of the cut. This is bad because it creates a very large wound for the tree to heal. Instead, we use a 3-cut approach. Starting out several inches or more from where we will make the final cut, we first cut on the bottom, upwards about 1/4 to 1/3 of the diameter of the branch. The second cut is made from above, and out from the first cut (away from the trunk) by an inch or more. The larger the branch, the more gap we want between these two cuts. What will happen now, as we make the second cut, the branch will break off and fall, but the first cut will prevent the bark from tearing away with the branch We now have a zig-zag shaped cut with a break in the middle. The third and final cut is made through the branch collar protection zone in order to leave a nice, clean cut that the tree can more easily heal.

To remove a limb without splitting the bark past the cut, use the 3-cut method, making cuts in the order shown.

Pruning Frequency

How often to prune a tree depends on the age of the tree, and your long-term goals. My advice here in Florida is that a tree should be pruned, or at least looked at and considered for pruning, once per year from when it is planted until it reaches about 20 years old. After that, every 2 years until age 30, and every 2-3 years after that. Does this sound like a lot of maintenance? (I can hear you saying “yes”), It may be, but consider the long-term benefit of well-maintained, healthy trees: they add value to your property, they provide oh so valuable and wonderful shade, they provide shelter to both wildlife and humans, and they are great for the environment (think locking up carbon that was carbon dioxide in the air, and releasing oxygen- nature’s tool against global warming). The thing is this, and I see it all too often in this business: most people don’t get their trees pruned like they should. They take a leave and forget it approach. Then, one day, they notice that branches from their oak tree are covering the house, the yard, and hanging over the fence. NOW they want the tree pruned. Guess what? Since they didn’t work with a tree specialist on an ongoing pruning plan, now they are having to remove long, unbranching limbs. These limbs are large, often 10 inches or more in diameter-and mostly dead wood. Do you remember what happens when we remove a limb that is mostly dead wood? Right- it opens the tree to decay and insect pests, and the beautiful tree that has been so long neglected is now put into a slow death spiral. I’ve heard it referred to as “incremental removal”, because that is what happens. This year, we remove several large limbs that have become a risk to the home, starving grass and other landscaping of light, and maybe even putting the neighbor’s home or other property at risk. Then the tree starts to decay from these large wounds that it is impossible for the tree to close before decay sets in. The decay spreads through the trunk, into the roots, and before you know it, termites invade the tree and begin their dastardly work of breaking it down. In a few more years time, the tree is weakened to the point that a few more limbs need to be removed because they are nearing collapse, or perhaps they have already failed. Ultimately the entire tree will need to be removed. In much of our service area, removing a “grand oak” requires a permit, and frankly, the guidelines for removal are so strict that they could be considered onerous. For help in determining if you need a permit to remove a tree, contact us here. We can help you navigate the permit requirements that pertain to you at no cost, and no obligation to use us should you decide to remove the tree. You will be much better off, and save money in the long run ( as well as gaining the added property value) if you take care of your trees by having them pruned before they become a problem. You may find, while working with your tree service company, that the intervals I mentioned earlier are not necessary in your case, and you can develop a plan that suits your situation. Whatever the case, planning ahead is always better than dealing with a lack of planning later. In the case of trees, a problem ignored only grows into a bigger problem.

Pruning Dose

Pruning dose refers to how much foliage we can remove from a tree at one time without causing too much stress on the tree. This number, per the ANSI 300 standards, is 25 percent. So, in order to not over-stress a tree, we should not remove more than 25% of the foliage, or canopy, at one time. If more reduction is desired, it is best to wait a minimum of 3-4 months for the tree to recover; more time is better. If more reduction is needed, you should work with your tree pruning specialist / tree surgeon to develop a plan. Your plan should prioritize what should be pruned now, and what can be pruned later.

Things to avoid when pruning a tree

Flush Cuts

Always remember the branch collar protection zone, and the second goal of making the shortest cut through the branch collar possible. Keeping these two concepts in mind will prevent the mistake of making a flush cut. A flush cut is when a branch is cut so close to the support limb or trunk that the branch collar is removed as well. This leaves a long wound with little to no protection from disease, and also creates a structural weakness. The oak tree below had a branch removed with a flush cut. A few days later a thunderstorm came through, and you can see the result. The best course of action now is to remove the entire limb at the trunk, so that it can heal there.

Topping a Tree, or Rounding Over

These two terms are used interchangeably, and although they are more of a pruning strategy decision than a pruning method, topping a tree can cause its demise. Topping or rounding over is an out-of-date practice from back when we didn’t know any better. The problem is again the fact that branches are not removed where the tree can compartmentalize the decay. Instead, branches are sheared off willy-nilly to achieve a desired shape. The goal is to round a tree, reduce its canopy, or both. Basically it’s trying to make a topiary out of a mature tree. Topiary pruning is a slow and somewhat arduous task that needs to occur over several years to train the tree to the desired shape, and it must be done while the branches are small enough that they do not have any dead wood. When an older tree is pruned like this, it can cause dire consequences. I took the following picture this past summer, when this tree should have been full of leaves. I was horrified when I went past this apartment complex in Lee County, and all of the trees were dead due to being rounded over. (Yes, I admit it- I’m a tree geek. I take pictures of trees everywhere I go- I can’t help myself. ) The trees previously were growing in a larger, more appropriate size, and that is how they should have been left. There are techniques for reducing the canopy size of a tree that will not kill it. Topping or rounding over is not one of them.

This apartment complex had 6 trees like this one, that had been rounded over. All of them are now dead. Not surprisingly, whoever did the pruning also over-pruned all of the palm trees on the property as well.

While the trees like the one above might appear to have branches small enough to handle a topiary approach (small branch diameter), there were plenty of larger limbs also cut off. This is a case where more like 80% of the canopy was removed at one time, and the stress was just too much for the trees to survive. Looking at the size of the trunk, you can see how inappropriate the finished size was for the age and size of this tree. Mistakes made: 1) more than 25% of canopy was removed; 2) pruning style was inappropriate for the size, age, and original form of the tree. 3) Heading cuts were made not at a branch collar, leaving the tree vulnerable to invasion of decay-causing organisms. The takeaway: if you ask the arborist of a tree service company to prune your tree a certain way, and they advise against it for the sake of the tree’s health- listen to them. Remember that you are paying for knowledge, not just labor. If you don’t get any advice or feedback on what is good for the tree, you might be talking to someone who is not that knowledgeable. Anyone can rent a bucket truck, and in Florida, anyone can start a tree service business with no qualifications. This is why I have taken the time to try to inform you, before something like this happens to you.

Pruning overhanging limbs

Pruning limbs that hang over a house, pool cage, or other property that cannot be moved can be quite challenging. Generally speaking, trimming large branches that hang over property like this should be left to the professionals, especially if the limbs have become large enough to cause damage if dropped. Even repairing something as minor as a bent gutter can end up costing more than it would have cost to have the limb professionally pruned- especially if you don’t get around to the repair right away, and rain water gets up under the roofing shingles or behind the fascia due to the gutter being damaged. In order to control the fall of an overhanging limb, a professional tree pruning service will use appropriate load-rated ropes, blocks (pulleys), and other specialized equipment that most homeowners simply don’t own. I have thousands of dollars invested in climbing and rigging gear for the specific task of pruning and controlling branches that pose a risk to property- and I could easily spend thousands more on additional gear if I wanted this or that latest gadget. Making a limb defy gravity and fall in a safe way not only requires this specialized equipment, but also requires a good idea of the total weight of a limb. (I use tables to help calculate the weight of a limb; I’ve seen guessing get people into trouble). With the added weight of foliage, Spanish moss, vines, or water a limb can weigh a lot more than it appears.

Pruning limbs that hang over buildings and other property is best left to insured, experienced professionals. Rigging these branches so that they fall away from the house requires specialized equipment and knowledge.

Do you have limbs hanging over parts of your house or other property that need professional help? Contact Tree Wise Guys now for a free quote . Remember, the longer you ignore a problem, the more it grows.

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