Another time for some pruning is when trees grow too wide and start to interact with your garage or house or those of the neighbors. There are only two ways to prune a branch like this without having it react strongly and produce rapidly growing shoots. One is to remove it at its origin point, the branch collar. This is not always a practical solution and sometimes removes too much branch, creating a visual problem, a space in the shape that doesn't look good. Many times a good result can come from the removal of smaller, side or lateral branches. What doesn't work is cutting off several feet of the end of the branch, thus forcing it to shoot profusely.

These ideas also work when trees bump into each other, with some added concerns. First, trees grew up together in forests before we brought them to our homes, so they can handle a little jostling and crowding. Here in our gardens they are planted beside other species that they would never have normally been exposed to. In these situations I tend to favor the underdog. A crab apple beside a blue spruce many times its size is in trouble, if the spruce is stealing its light and water. I usually prune the dominant tree. In the case of the crab and the spruce I would opt for some branch shortening of the spruce and leave the apple alone, as it has enough to worry about.

An old pruning idea is that of removing all crossing branches. There are many times when this just does not work. Consider a very densely branched tree such as a mayday. The mayday is not in error, and it knows what it is doing, so in some cases removing all the crossing branches would leave a scrawny, over-pruned, stressed tree, a victim of all theory and no practice, no knowledge, no experience. Every species has a natural pattern and it is to the tree's serious detriment to change it. A pruning job that tries to turn a mayday into an open-crowned look like a poplar is not a good pruning job.

That said, there are times when a long shoot wraps and twists it way upward through the crown; I normally remove these worst cases. If the form of the structure is not threatened by a few crossing branches, so be it. Another example is a branch that insists on growing from one trunk and heading inside toward another trunk, instead of heading out toward the light. Many of these I also normally remove. I like to see most of the branches growing out and up away from each other, each with its own space in the crown of the tree.
The old theory of crossing branches was that when the rubbing of the crossed branches had progressed to the point where the bark was worn through, this would be a serious site for disease introduction. Of the hundreds of these I have seen, I have never seen one of them infected with disease. Indeed, if the two crossing branches happen to be old enough to have grown into trunks, the loss of either would be a significant loss of energy-producing leaf mass, far outweighing the potential damage from disease infection sites that don't exist.
Always think of your pruning and other tree care practices from the tree's energy perspective. Always do the least harm, the greatest benefit for the tree. Water enough to keep the soil moist; don't do a lot of other planting under the tree. Don't disturb or compact the soil under the tree. Carefully consider your pruning, look a lot and accomplish your goals with the minimum of branch loss.

Another situation that arises I call the keystone. Think of a young tree, apple, mayday, mountain ash are the forms I am thinking of, any young tree at the stage in life where the mature form has been set and everything is looking good. Now imagine the central leader, or what once was, because now the tree has five or six main branches, trunks all heading in their own direction, and starting to develop a full crown. That central leader is now just another trunk, or branch inside the crown.

Two things can happen with this; because of applied old pruning theory, it may have received cuts to assist the other trunks, crossing, thinning would have been the ideas. The result is that its vigor has been reduced, its brothers and sisters are thriving all around, casting enough shade that at some point our old central leader is in trouble and not keeping up, over-pruned inside the crown and being shaded out.

The central trunk has a very important position within the overall form or architecture of the tree. It is the keystone and if it and its subsequent tissue below in the trunk were to die, a section of rotted wood would develop in the worst possible place. Right in the middle of the trunk we would have a dead spot where the leader was, now surrounded by all the spreading healthy sub-trunks. As time passes and they get heavier, the rot in the middle of the trunk progresses, a time bomb can develop, and this once magnificent tree could split apart, the sub-trunks splitting off that central rotten core.
There are two options through the years as this develops. One is to cut the leader out when it is still small. If done early, the subsequent deadwood inside the trunk would be minimal, and not be able to create a dangerous volume of dead tissue inside the trunk. The second, which I favor, is to recognize all this and maintain the tree in such a way so as to assure the original leader's position in the crown and to make sure it gets enough light. Also, if crossing thinning issues arise, prune the outside trunks instead, keeping the leader vigorous.

I have seen many examples of these keystone trees in maturity. Some required bolts and cables to reinforce them, others required removal.
There is a lot of pruning done in this world that doesn’t work with the way the plants are designed. There are ideas, techniques and methods that when understood and employed, do not cause a strong growth reaction from the tree. Heavy pruning, shaping, hedge work are all usually performed internodally, that is at places where the plants are not designed to be cut. And the tree reacts accordingly by doing its best to regain the lost leaf mass. When trees and shrubs are cut at internodal sites, it always provides the stimulus to rapidly replace the lost leaf mass. This is why you can trim a hedge several times a year. Buds latent in the bark, waiting for such emergencies, are deployed and start new shoots that are being asked to replace the lost leaf mass.

What are nodes and why does the tree react so strongly when pruning ignores them? Nodes are points along branches that will develop first a bud, and then a branch from that bud. Nodes are meristematic points. Nodes are points where the branch is designed to abscisse if needed. Abscission is the natural removal of plant parts. Flowers, leaves, twigs and whole branches are naturally removed from plants, and always at natural junctions, abscission sites. This is a tidy arrangement and once understood, abscission sites are easily recognized. When it comes to woody parts, apart from flowers and leaves, trees almost always abscisse at branch collars. This collar is the branch’s origin point and where it is naturally designed to be removed, either through abscission or pruning.

The vast majority of my pruning occurs at branch collars; it is the kindest cut. By removing entire branches, no matter how large or small, you elicit the least reaction from the tree. It is the tidiest, most common sense way to work with woody plants. Try to accomplish your pruning goals without forcing the tree to react to your work. This achieves a couple of important goals. Your pruning job will last longer; pruning that stimulates the plant into a quick reaction to replenish lost leaf mass will by next year need to redone. That’s not so with the clean collar cut approach.

You can also easily over-prune a tree using the branch collar technique. A serious leaf loss, collar cuts or not, will eventually generate a response. Percentage is a handy tool when thinking about your pruning job. An old saying from the days of serious misinformation about trees, said never remove more than a third, 33% of the canopy, at any one pruning. But removing anywhere near that much is highly damaging, a very aggressive pruning job, outside of stewardship, common sense and kindness.

We know that a tree is a balanced system. Root hairs, woody roots, trunk, branches, twigs and leaves, all grow in sync. The removal of 1/3 of the branches, 1/3 of the food generating tissue, would be perceived as an attack and emergency responses throughout the tree would go into action. The result seen on the outside of the tree would be the quick generation of many new shoots to try to replace the lost leaves as soon as possible.

I consider a 10% overall leaf loss a major pruning job and call it good enough for that year. If major things have to happen, spread them out over a two or three year span, show a little kindness. This is an amazing living being that deserves and appreciates your respect. Prune smarter, not more, look many times, cut once, have a plan. Especially on younger trees, a few thoughtful cuts get the job done with minimal leaf loss.

All of these ideas are aimed at one thing, keeping your tree as strong as possible. When trouble comes, drought, insect attack, storm damage, you name it, your tree will withstand it as prepared as possible, and most likely get through it.

We need to talk about training cuts, branch shortening cuts. If it is not possible to remove the whole branch at its collar, and shortening it is your only option, then go ahead. There is no natural position on the branch, such as the collar, to do this. What we do is ask a lateral branch to be the leader. Be respectful of the lateral’s branch collar, leave some space, don’t cut into the collar. The larger the training cut, the stronger the branch’s reaction. Make a big cut and you will elicit sucker growth for sure. This growth may frustrate you and a year later might need to be pruned again. If possible, remove the branch either at the trunk at its collar, or at a lateral branch. Cutting anywhere else is an internodal, between nodes, cut.

When making collar cuts always cut the branch off first, leaving a good stub. If you are sure the branch needs to go, then cut it, get it out of the way so you can focus on the correct collar cut. If the branch is too big to control with one hand, make an undercut first, then finish cutting from the top, to guarantee you won’t create a tear-out. A tear-out is where the uncontrolled falling branch rips away the bark from the branch, its collar and sometimes the bark of the trunk. It is a loss that a little care in branch removal will prevent.

Before you do any pruning know a little about your tree, what species it is, how it compares to others you have seen, its normal look, the density of this type of tree. These and other questions are good to ponder. Each species has a pattern, a look that is normal. When I prune I look a lot, I make a cut or two, then stand back and assess what I have done. Look a lot, prune a little, you can’t go wrong.