JoAnne Skelly: Pruning for tree health

Proper pruning can be good for trees. However, people often damage trees in the name of pruning. Dr. Alex Shigo, a well-respected tree researcher provides a number of valuable tips in his book “Tree Pruning.” Often when pruning trees, people only think about their personal needs from the trees and pay little attention to the fact pruning affects the health of trees. Shigo points out proper pruning preserves tree beauty as well as its defense systems. Proper care starts with an understanding of how trees grow.

Trees can live longer than any other organism. A tree is made up of wood — living, dying and dead cells in an ordered arrangement. Sapwood is alive and is located in trunks, branches and roots. These living cells store energy reserves used in many tree processes, including defense. Pruning, if done improperly, can damage sapwood, which can impact growth and inhibit defense mechanisms.

Proper pruning avoids flush cuts or stub cuts, which injure trees and destroy a tree’s ability to keep disease organisms or insects out. A flush cut damages the branch collar. The collar is that part of the tree that compartmentalizes the injury (in this case the pruning cut) from the rest of the tree. It’s the “donut” shape that develops after a limb has been pruned correctly. Stubs are branches that aren’t cut close enough to the branch collar. There’s no way the protective donut can develop with a stub in the way.

Topping causes serious injuries to trees and leads to hazardous conditions. Over-pruning destroys a tree’s framework, weakens roots, and initiates excessive weak sprouts that become hazardous. Wound dressings don’t stop rot and may actually stimulate rot in some cases.

Proper pruning begins with selecting the appropriate tree for the planting site. Know the soil type and drainage. Don’t plant trees that grow large, such as a sycamore, in small places, under power lines or close to buildings. Buy healthy trees free of wounds or injuries. Start pruning after three years of planting to establish the framework shape of the tree. Prune only one-quarter of the entire tree each year. Prune regularly to maintain the structure of the tree.

Use sharp tools when you prune. Don’t work near power lines. Hire a professional arborist if the pruning job requires a ladder, a chainsaw, if the tree has been storm-damaged, or limbs are greater than two inches in diameter.

JoAnne Skelly is Associate Professor & Extension Educator, Emerita at University of Nevada Cooperative Extension. She can be reached at


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