Trimming Trees – How Much is Too Much?

By James Donegan

How much is too much when it comes to thinning out live growth in the crown of your trees? At Donegan’s Tree Service, when maintaining the health of a tree, we think that no more than 1/3 of the live growth should ever be removed in one growing season; any more than this can compromise the health of young or mature trees. In line with that, we believe that less thinning is better. Although lightly thinning the entire tree can be useful to increase air and light flow, it still should not exceed removing more than 1/3 of the live growth in one season.

Structural pruning should be considered before the entire crown is thinned. In fact, structural pruning is probably the best way to thin. A practical approach would be to structurally prune to reduce defects, and then thin out the crown to shape and balance the tree to be aesthetically pleasing if the maximum pruning allotment has not been met or exceeded.

Unfortunately, many inexperienced tree companies will prune when it is not necessary, or they misapply or misunderstand thinning, and subscribe to the practice of only removing branches from the interior of the crown. This is often referred to as “lion’s tailing,” overlifting, overthinning, stripping out the interior, or cleaning out to create a vista. Incorrectly thinning a tree means little or nothing is removed from the ends of the limbs, and this is a mistake. Lion’s tailing causes structural weakness because all of the foliage left on the ends of the branches causes them to be heavy and unbalanced, putting too much pressure on the area where the limbs are growing out from the trunk. It sometimes results in splitting branches and other safety hazards, making the tree more susceptible to storm damage from high winds and the additional weight of ice. It can also lead to the decline or death of older, mature trees, as you can see in this video.

In addition to being a bad practice, unprofessional tree services will also overcharge when making these incorrect cuts because of the enormous amount of brush on the ground that they will have to carry away. So remember, when it comes to tree trimming: less is better.