Written by Steve Geist, Senior Consulting Arborist
One of the most time-honored questions (or controversies) in all of tree care is, “when is the best time of year for trimming a tree?” Much has been written over the years, with various and contradictory opinions and theories offered.
In the day, pruning was referred to as tree surgery. For example, when Swingle was founded back in 1947, the company was known as Swingle Tree Surgeons.
For a moment, let’s consider the notion of tree surgery. Before surgery, the “patient” should be in the best possible condition prior to the procedure, thus minimizing unintended side effects and issues, while decreasing the recovery time.
Dead and broken branches may be removed at any time during the year. Where the real controversy exists is when is the best time to prune live branches from a tree or shrub?
In most cases, pruning in the dormant season (after the leaves have fallen from the tree) is the best time to surgically remove or prune live branches. From the tree or shrub’s perspective, the dormant season is an ideal time for trimming a tree.
Landscape plants spend their entire growing season storing energy to last through the winter and produce leaf and flower buds the following spring. Trees and shrubs are the strongest (in the best possible condition) during dormancy. This is when they are best able to defend the open pruning cuts from disease and decay organisms.
Dormant season is the ideal time to avoid encounters with insects and diseases of trees. These encounters would be unintended side effects. Many insects are attracted to scents or smells that the trees emit from the open pruning cuts. Insects harm trees by feeding and boring into plant tissue.
Several insects also spread diseases along the way. Dutch elm disease, thousand cankers of walnut, blue stain of conifers, fire blight, and drippy blight of red oak are all diseases spread by insects. Most wood boring insects that will cause serious harm to trees and shrubs are also dormant or immobile during this time of year. Therefore, pruning in the dormant season will reduce or eliminate the insect attraction to open pruning sites.
Lastly, for leaf bearing trees, it is far easier to see the branch framework without the leaves. The question will often arise, “can an arborist pruning a tree tell if a branch is dead or alive without foliage?”
The answer is a definite yes. Leaf buds, branch flexibility, and bark appearance are all diagnostic clues for branch viability. Seeing the tree’s framework is important in identifying crossing and interfering branches, seeing branch defects, and determining branch health – or which branches are most important to the tree. Branches with more foliage buds are more important to the tree than branches with a few green tufts at the canopy edge. The weaker branches (which should be pruned) are more easily identified in the dormant season.
So, are there any pitfalls to dormant pruning when you’re thinking about trimming a tree? There are a few. Sheared plants may be damaged or scorched if pruned during cold weather. Spring flowering shrubbery should also not be pruned in the winter, as the pruning will take the flower buds along with the pruning cuts – diminishing your spring display.
When in doubt, make it easy on yourself and call Swingle today to assess your pruning needs. Your consultant can determine what can be pruned during the dormant season and what should be done in the spring.
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