The Art of Pruning

Of all the things I do as a horticulturist, I receive the greatest joy and satisfaction when I prune, especially on trees. It affects me in an interesting way. I feel an interesting communion between the tree and myself, and sense a certain sublime bonding. I know that when I, as Alex Shigo so beautifully puts it, ?touch trees?, I am affecting and guiding that tree?s life, in often profound ways, and for many years to come. The tree is changed forever, and if I practice the skills and apply the knowledge that I?ve learned as an arborist, the work I do helps to maintain or improve the tree?s health. But there?s more to it than that.
 
Pruning is an art, plain and simple. Sure, we need to understand the biology and nature of the tree. We also need to apply the skills and techniques of a good tree worker. But the best arborists are also artists?tree artists, as it were.
 
My first concerns when working on a tree, are to attend to the structural and biological needs of the plant. I look for potentially weak crotches and remove the offending branches, hopefully before they?ve gotten so big that their removal will leave an awkward or unbalanced specimen. I take care of rubbing branches, remove dead wood, and attend to wayward branches crossing back into the center, or growing into pathways, or blocking important views. If I have the opportunity to practice my skill as an arborist as I would like, I?ll have the chance to take care of such (potential) problems while the tree is still young. In fact, it is in training and maintaining young trees, that I have the greatest opportunities to practice tree care as art.
 
It is in the early years of a tree, say through the age of five or ten years, when we make those decisions that will determine the tree?s future structure. It is in then that we have the opportunity to choose a branch with an unusual or wild shape over those that are less aesthetically interesting. It is also when we can make heading cuts, or cut back to laterals that will take over as lead branches, to create the shapes and curves and angles that will later become the large laterals of a truly beautiful specimen.
 
When two lateral branches are in competition for space, and one must go to allow the other enough room to grow, as arborists it is our job to determine which branch to keep, and which to remove. My first priority in making such a decision is to ascertain the structural soundness of the branch to remain, for it would be truly a pity to carefully remove the one, only to have the other branch brutally ripped off in a windstorm. So I check to see if either has a weak crotch.
 
For those of you who aren?t sure just what constitutes a weak crotch, let me try to explain. A weak crotch, also known as a weak branch attachment, is more likely to occur when the angle of attachment between two branches is narrow. It is under those circumstances that the bark, a nonliving tissue, is more likely to become pinched, or ?included?, between the two limbs, or between the limb and the trunk. As a visual example of what I?m talking about, use your forearm and upper arm. If you hold your forearm out at an angle from your upper arm that is wide, say about 90 degrees, you will be able to see your skin continuously from one end to the other. But as you bring your forearm up, you will notice that the skin in the crotch will begin to disappear between the two. That disappearing skin is analogous to included bark. The bark being pinched between the two branches is nonliving tissue, and no attachment occurs at that point. Look at your arm again in that more upright position. The pinched bark acts like a split, or a perforation between the two branches, right at that point of greatest stress. Hence the term weak crotch, for it is in such cases that the likelihood of branch failure is greatly increased. That is why it is one of my foremost priorities to remove such branches as early as possible, without overpruning.
 
Strong crotch angle
 
A strong crotch, and hence, strong branch attachment. The angle is wide enough, approximately 70 or more degrees where the two branches come together, and the wood is continuous and not ?pinched?.
 
Weak crotch angle
 
A much weaker crotch and branch attachment. The angle is approximately 40 degrees and you can see how the wood has become ?pinched? in between the two branches. The dark stain emanating from the crotch is due to sap oozing from the stress on living tissue caused by the included or pinched wood.
 
But I have digressed a bit, and I hope that the reader will forgive me, for it is so important to take care of weak crotches early.
 
However, if one of two branches needs to be removed, and both have a good wide angle of attachment, it is then that my skills as an artist come into play. I begin to look at the structure of the branches for their potential aesthetic value. I like natural and wild looking branches, ones that have a lot of curvature, and changes in direction. It is those kinds of branches that have the most visual appeal. Gentle s-curves and sudden changes in direction can be incredibly attractive within the structure of a tree. Don?t ask me why. I imagine the answer lies deep within the psychological subconscious.
 
It is even possible, with a bit of foresight, to create such wildness and curvature within a limb. The key is to do such pruning early enough in the trees formative years. Here?s how to accomplish such a result. If you have a straight young limb with little curvature, you can cut that branch back to a lateral or secondary branch that is positioned to grow in an appropriate direction, and you create, over time, a curve or change in direction. As that limb matures, the evidence of the cut will largely disappear, and the limb will have a very natural looking sway or curve to it. The same result can be achieved by cutting a very young branch back to a bud that is well positioned to grow in a desired direction. For example, if you carefully cut a young branch back to a bud that sits on the topside, that bud will grow into a branch that heads up and away from the original direction. If you cut to a bud on the left side of the branch, the same thing occurs, but the branch that results will grow more to the left than the original branch would have, and you have created a curve in the structure of the branch. If you take that same branch that you redirected to the left, and later select a branch or bud that is on the right side of the branch, you will have created an ?s-curve?. It takes patience and foresight and time to do this, but when it happens, you as an arborist have created an artistic and aesthetically pleasing effect. Ah, yes?tree art!
 
Another challenge I encounter when training young trees is to find a way to eliminate the all too frequent cluster of lateral branches at one point of attachment. It seems that the nurseries have gotten into the habit of topping young tree stock, to create the full head of foliage that apparently helps to sell such trees. Mind you, as an experienced arborist, I reject or pass over such trees regularly. (The preceding is a hint to my friends in the tree nursery business). Unfortunately, I sometimes have to contend with structurally unsound trees that have already been planted and accepted. It?s not uncommon to find trees that have 3 or 5 or more branches all coming off of the trunk at one common point. Once the tree has had a chance to establish and recover from the shock of planting, as soon as possible, begin removing the excess laterals. Know that if you do so early in the life of the tree, even if it creates temporary visual imbalance, the tree will recover, and new foliage will quickly enter to fill the space created and eliminate the visual gap.
 
Poor branch spacing
 
This almond tree shows poor branch spacing?there are way too many permanent limbs all attached at the same point.
 

 
Good branch spacing
 
Further up in the canopy of an almond tree, the spacing is much better. The branches are well separated, usually by at least 1 foot, and they radiate out in all directions.
 
However, if those branches have already matured a bit, and the removal of any given one will leave too large a gap within the foliage as to be acceptable, another option is available. You need only use the same technique of cutting the lead branch back to a lateral that is substantial enough to fill most of the potential hole within the foliage. This will slow down the growth of the branch that has been cut back, and allow other remaining branches to start to grow into the area formerly occupied by the removed branch. To further encourage the remaining branches to fill the area, I will also remove other small laterals that are growing into the area that I want the branches I am keeping to fill. Later in the year, or perhaps the next year, after the other branches have begun to fill the gap, I will then completely remove the offending branch, and the hole left in the foliage will have largely been mitigated. It is in this way that I can remove offending branches without leaving unpleasing gaps within the structure of the tree.
 
One final thought in achieving artistic pruning. I believe it?s important to frequently stand back from the tree far enough to be able to see the entire tree in one glance. It is from that position that one can best see the overall structure and balance. It is from there also that you can ascertain as to how heavily you have already pruned. It?s reminiscent of the old saying of ?not being able to see the forest, for all the trees.? If you spend all your time in the tree, you might ?not be able to see the tree, for all the branches?. Remember to especially view the tree from the angle that the public or your client will most frequently see the tree.
 
With that, I wish you all happy, healthy and safe pruning. Go out there and touch trees. Work with nature to create that most magnificent of art?beautiful trees.