Pruning is a fundamental practice in the tree care industry. When a customer calls for help with a tree, the two most likely concerns are: something is wrong with my tree, it looks sick; or my tree needs to be pruned. In some cases, previous poor pruning practices caused the current problem. As such, a review of the salient points is worthwhile, especially for new tree care workers.
Pruning young trees
Providing good parenting and guidance when children are young will yield huge benefits for them in their teenage and adult years. The same is true for woody plants. In general, ornamental trees, such as crabapple and black cherry, can be trained to several trunks, while shade trees should be pruned to develop one strong central leader. The branches of young trees should only be removed for good reason.
Many pruning targets can exist with young trees. Experienced arborists are able to simply stand 5 to 10 feet away from a young tree and easily spot problems in the making or existing defects. The first is the presence of a codominant leader. Unfortunately, many young trees possess a terminal that has two or three equally sized and arranged leaders. As early as possible in the growth of the tree, one should be selected to remain in the structure of the tree and the others. Likewise, shorter but similarly arranged branches that are growing straight up should be removed to prevent future competition with the leader.
Other common targets are rubbing, crossing or closely parallel branches. These are all a cause for concern, as they can damage the tree’s bark. This damage creates entrance wounds for various fungi, reduces water and nutrient flow, and prevents the establishment of sound architectural structure within a tree.
Broken branches are an obvious target. In most cases they should be removed back to the trunk or a main lateral branch to avoid sucker growth and unwanted interior sprouting. Branches that drag on the ground or are headed downward are also targets. Generally, these are weak, small-diameter stems that compete with other maintenance operations in the landscape. An exception to this target would be a specimen tree in an arboretum or botanical garden setting, where these branches are prized for the interesting appeal they present to visitors.
In short, any branch growing straight up, straight down, rubbing and crossing, broken or strongly competing with others should be considered for removal.
Once the targets or obvious defects have been removed, it’s beneficial to develop scaffold branches. These should be selected for strong attachment, 45 degrees is a good rule of thumb; appropriate size, no more than half of the diameter of the trunk; and good spacing relative to other branches. Spacing should be considered both vertically and radially on the trunk. For larger trees, spacing should be 18 to 24, Inc.hes apart, whereas 12 to 15, Inc.hes is reasonable for smaller trees.
When considering which branch is best for removal, a good guide is to think smaller instead of larger whenever there is a choice between two branches. Removal of the smaller branch leaves a smaller wound, which is easier for the tree to close and compartmentalize. As discussed in previous articles, trees don’t “heal,” rather they close off the wound and isolate, or compartmentalize, it from outside forces that may degrade the inner heartwood.
This process can be done in a single visit to a property; however, several visits, evenly spaced between the first few years of growth, is preferable. Remember, the removal of stems and branches diminishes the sugar/carbohydrate production potential for the tree, and as such should be performed over time rather than all at once.
Pruning cuts for older trees
Before any cut is made, the placement of the saw is crucial. In addition to the previously identified scaffold limbs, leader and stem defects, two other parts of the tree’s anatomy need to be identified and used in consideration of branch removal.
The branch collar, sometimes referred to as a shoulder, is the slightly swollen area just below where the branch attaches to the main stem. For most trees, the best place to make a pruning cut is just outside this tissue. The exact location of the collar varies from species to species. Pines, for example, have little identifiable collar tissue, while it can be clearly seen on most maples. Generally, spotting the collar is a technique that is best passed on from experienced arborist to new tree worker. Pruning at this spot closely replicates the location where branches would shed naturally from a tree.
If the location of the collar is difficult to determine, identifying the branch bark ridge (BBR) may be of help. The BBR is a section of crinkled or closely compressed bark located between branches, usually in the branch crotch. The pruning cut should not be made here, but it can be helpful as a first identifier. Once the BBR is identified, attention should be focused outward, towards the base of branch attachment to the branch collar.
Crown cleaning is beneficial to remove dead, diseased, broken or weakly attached branches within a tree crown. This type of pruning should be done on a regular basis to correct small problems before they develop into big ones. Crown thinning is called for when light penetration and air movement through the crown is necessary, such as when golf course superintendents strive to keep valuable trees in the golfscape and allow turfgrass to grow well underneath, or when the tree has a history of foliar disease and increased airflow will serve to reduce the chances of reinfection.
Thinning should be accomplished along the entire length of a limb rather than just on the portion close to the trunk, which is a common request of many homeowners. When thinning, care must be taken to retain the tree’s natural shape and structure, as clearing out too much inner foliage can cause an effect known as lion-tailing. Trees with this condition are more prone to breakage in storms. At the very least, the procedure is an energy drain on the tree. Instead, efforts should be taken to maintain well-spaced inner lateral branches to achieve even distribution along the branch.
Crown raising, the removal of lower branches to provide access or clearance for buildings, pedestrians or signs, is often a necessity, especially in urban settings. Care must be taken not to remove branches excessively to avoid depletion of energy reserves and retain the development of trunk taper and structural stability.
When the height and spread of a tree must be reduced, the practice of crown reduction can be utilized. This involves cutting limbs back to their point of origin or laterals that are sufficient in size to sustain the remaining portions of the limb and retain apical dominance. Generally, when a branch is cut back in this manner, no more than a fourth to a third of the foliage should be removed.
Topping, or cutting branches back to a stub or branch that is not of sufficient size is not a recommended tree care practice. Topping is commonly seen when inexperienced tree care providers attempt to fit a tree of significant size into an insufficient space.
Neglected trees that have not been pruned or trained as needed through the years often have codominant leaders, rubbing and crossing or broken branches, or branches dragging on the ground. Care must be taken to work on these trees in stages to avoid nutrient depletion and the production of water sprouts on the interior limbs, a sure sign of overthinning.
Timing simply cannot be overlooked. Some individuals, like Wayne Gretzky and Henny Youngman, are born with it, while others have to work on it. In terms of tree pruning, the dormant season is generally considered best in order to minimize the risk of disease and insect problems associated with wound entry, as well as to take advantage of a long period of time to facilitate closing and compartmentalization.
Even though the dormant season is preferred, the old adage, “when the saw is sharp,” may also apply, especially following storm damage or when an immediate need is present. Other considerations apply as well. For example, certain tree diseases, such as oak wilt, are more likely to spread when trees are pruned during the growing season. And tender-barked trees are best pruned when sap flow is lowered, as tearing of bark is less probable.
When trees are significantly hazardous and located in a target rich environment, the decision of where to make the pruning cut becomes much easier. Trees with several defects — codominant leaders, lean, decay, cracks, basal root plate defects or girdling roots that extend over houses or locations where people or valuable property exist — should be examined to determine if they pose a risk greater than is reasonable to tolerate. In such scenarios, tree removal is recommended.