Tree Trimming

Trimming Mature Trees

Trimming is the most common tree maintenance procedure. Although forest trees grow quite well with only nature's trimming, landscape trees require a higher level of care to maintain their safety and aesthetics. Trimming should be done with an understanding of how the tree responds to each cut. Improper trimming can cause damage that will last for the life of the tree, or worse, shorten the tree's life.

Reasons for Trimming

Because each cut has the potential to change the growth of the tree, no branch should be removed without a reason. Common reasons for trimming are to remove dead branches, to remove crowded or rubbing limbs, and to eliminate hazards. Trees may also be trimmed to increase light and air penetration to the inside of the tree's crown or to the landscape below. In most cases, mature trees are trimmed as a corrective or preventive measure.

Routine thinning does not necessarily improve the health of a tree. Trees produce a dense crown of leaves to manufacture the sugar used as energy for growth and development. Removal of foliage through trimming can reduce growth and stored energy reserves. Heavy trimming can be a significant health stress for the tree.

Yet if people and trees are to coexist in an urban or suburban environment, then we sometimes have to modify the trees. City environments do not mimic natural forest conditions. Safety is a major concern. Also, we want trees to complement other landscape plantings and lawns. Proper trimming, with an understanding of tree biology, can maintain good tree health and structure while enhancing the aesthetic and economic values of our landscapes.

When to Trim

Most routine trimming to remove weak, diseased, or dead limbs can be accomplished at any time during the year with little effect on the tree. As a rule, growth is maximized and wound closure is fastest if trimming takes place before the spring growth flush. Some trees, such as maples and birches, tend to “bleed” if trimmed early in the spring. It may be unsightly, but it is of little consequence to the tree.

A few tree diseases, such as oak wilt, can be spread when trimming wounds allows spores access into the tree. Susceptible trees should not be trimmed during active transmission periods.

Heavy trimming just after the spring growth flush should be avoided. At that time, trees have just expended a great deal of energy to produce foliage and early shoot growth. Removal of a large percentage of foliage at that time can stress the tree.

Information from The International Society of Arboriculture