“Don’t top trees” is the horticulturist’s battle cry. The technique of of cutting back the upper limbs on mature trees to stubs of a uniform height is nothing short of tree mutilation. The tree is sheared like a hedge. Topping also is known as heading, stubbing or dehorning. No matter what it is called, it is a bad pruning practice.
Topping not only butchers the appearance of a tree, it reduces the leaf surface area available for the tree to produce the energy it needs. It starves a tree and depletes its stored reserves. This in turn can prevent roots from growing and supporting the tree. The large wounds created by this so-called pruning technique are unable to close. Open wounds are entry points for diseases, insects and fungal decay, which can then spread through the trunk and kill the tree. Topping injures the bark of the main trunk by increasing sun exposure. Each of these factors stresses a tree and can shorten its life.
In addition, topping creates a hazardous tree. The multiple new stems (water sprouts) that emerge after topping are very weakly attached to the parent branch and prone to wind and storm breakage. This practice also can reduce real estate value because of the tree’s ugly appearance and the associated safety hazard.
Why are trees topped? Some homeowners think they can control the height of a tree by having it topped. They mistakenly think a tree is safer if it’s shorter. The weak attachment of the water sprouts is actually more dangerous than the healthy long branches. Water sprouts have no structural connection to a tree, whereas regular branches attach to the parent branch and then into the trunk, adding more layers of wood each year. People also top trees because they interfere with power lines, buildings or limit the sunshine in a yard. A tree that requires heavy downsizing pruning every five to seven years is too large for the site. It should be removed and replaced with a smaller species.
Before hiring a pruning company, ask if it is an International Society of Arboriculture-certified arborists and check that certifications are current. Ask if the company tops trees. If it answers yes, you might want to avoid hiring the company. Once a tree is topped, it is difficult to correct, requiring years of selective pruning. The damaged visual appearance never really disappears. Avoid topping trees in the first place.