JoAnne Skelly: Pruning evergreen trees
November 14, 2018
We're pruning pine, incense cedar and spruce trees now. Some have branches hanging in the way of the driveway or gates. Others have dead or dying branches. We had delayed pruning until after a hard freeze to reduce the possibility for beetle attacks. When a tree is pruned, we're wounding it. This causes the tree to release chemical signals that can attract beetles to infest the weakened tree. However, beetles are no longer active after freezing weather, so now is a safer time to prune. The good news is most evergreen trees need little pruning. Some, such as dwarf Alberta spruce and nest spruce are actually intolerant of pruning.
You can't contain the size of a tree by pruning. "Select plants based on mature size to minimize pruning needs. If frequent pruning is necessary to keep plant growth in bounds and prevent interference with a walk, driveway or view, consider replacing the plant. Evergreen trees and shrubs are pruned according to species growth characteristics" (Whiting, Cox and O'Meara. 2006. https://static.colostate.edu/client-files/csfs/pdfs/618.pdf).
Before pruning, make sure the tools are sharp and clean. Sharp tools make good cuts without damaging branch tissue. Clean tools prevent the spread of disease. Since every pruning cut is a wound to the tree, it's important to keep the wound damage to a minimum. At the base of each limb where it connects to the trunk is a "branch bark collar," which allows a tree to compartmentalize and close up the wound. Remove a branch back to the trunk just outside of the branch bark collar. Don't injure the branch bark collar, or the cut will never callus over and the tree will always be susceptible to diseases and pests. Don't make flush cuts up against the trunk.
Remove a branch in the three-cut method: Make the first cut an undercut 12 inches to 15 inches out from the trunk, one third to half way through the branch. The second cut occurs on top of the branch a couple of inches out past the first cut, removing the branch. This initial double-cut method prevents the weight of the branch from tearing the branch bark and tissue below the branch bark collar into the trunk. With the final cut, remove the rest of the branch carefully, just outside the branch bark collar. Avoid pruning the central leader.
Proper pruning at the right time of year helps keep a tree healthy and strong.
JoAnne Skelly is associate professor and Extension educator emerita at University of Nevada Cooperative Extension. E-mail email@example.com.