By Tim Clancy, for Let’s Talk Plants! September 2024.
Pruning Trees
All things being equal, an unpruned tree will always grow faster than one that has been pruned. Pruning ornamental trees accomplishes many things such as providing clearance from buildings and signs, removing dead and dying branches and preventing the obstruction of desirable views. Irrespective of all those interesting outcomes, pruning is first and foremost a growth regulator.
Removing parts of plants, usually entire branches or parts of branches and also depending on objectives, buds, roots, flowers and fruits are sometimes removed. This has been done for thousands of years and is recorded in the Bible. Fruit farmers and arborists prune more frequently than foresters who prune considerably less often, each group having different objectives.
In the for-profit forest sometimes, lower branches are removed to produce knot free lumber. Most young forest trees will die of suppression before they reach harvest size. So, pruning to produce knot free wood will typically not be financially beneficial. It should be done very selectively in trees that are likely to survive in the forest.
Cladoptosis is the natural pruning process where a tree will shed small branches in the crown. Bald cypress, incense cedar and redwoods are examples of species that shed branches by this process. This is a type of natural pruning. Many pruning experiments have been carried out on forest trees and the results of these experiments are used in management decisions of trees in forests scheduled to be harvested. Most of these have been done to try and coax more usable product from trees at a faster rate. Alas, you can’t fool mother nature and these attempts at increased wood yield through pruning have proven unsuccessful.
Fruit trees are primarily pruned to ensure high quality fruit and to control tree size for maintenance activities such as pest and disease treatments and fruit harvest. Each tree species and cultivar will have different reactions to pruning. Tree vitality, pruning timing and pruning dosage all factor in the tree’s response. In the case of apples fruit size, red color, soluble solids content, sugar content and fruit acidity are increased by high intensity light which often is a result of pruning. Reducing the number of fruits will increase fruit size. Over-pruning can result in rapid growth of foliage which can inhibit light penetration into the canopy. This results in fewer and smaller fruits.
Pruning of ornamental trees objectives are different than the objectives of previous pruning types. Inducing flowering or fruiting sometimes comes into play. Like many things in life, pruning is important. A light pruning can be done at any time with little worry about a huge response from the tree. The best time to prune shade trees for maximal dwarf effect is when seasonal growth is nearing completion. This is usually late spring to mid-summer.
Christmas tree pruning is critical to create a product that the public will embrace. Christmas trees are sheared, also debudding may be helpful. To get the classic Christmas tree shape the trees are sheared into the familiar conical shape on a routine basis. Removing the branch tips removes auxin which is a natural growth regulator.
Pruning objectives help clarify the desired outcome and objectives vary depending on the desired management level.
Tim Clancy & Associates LLC
P.O. Box 1180 – Cardiff-by-the-Sea, CA 92007
International Society of Arboriculture Certified Arborist No. WE-0806A
International Society of Arboriculture - Tree Risk Assessment Qualified
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