Question: Trees growing along city streets and in an area parkway have been severely cut back at the top of the tree. Is this a common practice? Will it hurt the tree? — T.W.
Since deciduous trees are dormant at this time of year, it is a good time to prune them. Yet, from what you describe, these trees have been “topped,” a severe type of pruning in which the top of the tree essentially receives a buzz cut, removing a large portion of the tree’s canopy and leaving it with a flat top.
The tree will respond to this drastic pruning by producing fast-growing sprouts, which will be structurally weak. Over time, as these sprouts grow, they will develop into branches angled too close to the trunk of the tree, resulting in a weak branch arrangement.
Other negative impacts of topping trees is the reduction in food producing leaves and opening the tree to possible infection. When large trees get topped, they no longer have enough foliage to produce adequate amounts of food proportionate to the size of the tree. This will stress the tree and increases the risk of pest and disease attacks. Removing large branches from trees wounds the tree, and it will take time for these wounds to heal over, increasing its susceptibility to decay.
Granted, there are some bona fide types of pruning, such as coppicing and pollarding, which mimic topping, yet these methods are usually employed as a specialty management technique and are performed on plants that respond well to these types of pruning methods.
In order to maintain utility lines, municipalities and tree care companies need to prune large branches from trees and to remove any obstructions from wires and other equipment. This could be averted during the initial planting of the trees by keeping them a fair distance from any overhead lines or utility equipment.
Pruning is a good management tool to keep trees healthy and to add aesthetic value to the community. During this time of year when trees are void of foliage, it is easier to visually inspect a tree’s branch structure and to prune with the tree’s natural growth habit in mind. Broken or diseased branches, as well as those that rub against each other, should be always be removed.
Use the three-point method of branch removal to properly prune large branches instead of “topping.” The first step is to relieve weight from the branch by undercutting halfway through the branch at a distance of 12 to 18 inches from the limb’s point of attachment. The second cut is made further out on the branch from the first cut (further meaning away from the trunk) by cutting the entire branch from the tree. The third and final cut is made near the branch collar by cutting through the entire branch stub. Do not cut branches flush with the tree trunk.
A visual of this three-point pruning method can be found in an online factsheet: hort.uwex.edu and type XHT1014 into the search box.
— Jeanne Hilinske-Christensen is the UW-Extension Interim Horticulture Educator for Kenosha and Racine counties. Submit plant care questions to the Master Gardeners Plant Health Advisers. Phone 262-857-1942 or email email@example.com.