Garden Variety: Topping harmful to trees

Tree experts and professional arborists have agreed for decades that the pruning practice known as topping is detrimental to trees, but it continues to happen across the country and right here in Douglas County.

Maybe you saw your neighbor do it, or your parents used to do it that way, or some guy with a chainsaw told you it was OK — whatever the case, let's work toward better pruning practices for the future.

Topping is also sometimes called heading or hat-racking. When a tree is topped, limbs are cut back to large stubs, like an arm chopped off at the elbow. The typical reason for topping a tree is to reduce the overall size of a large, mature tree. Sometimes property owners report doing it simply because they believe it is good practice, like getting regular haircuts. Silver maples and Siberian elms are popular species for topping in the Midwest.

Topping is detrimental to trees because of the large wounds it creates. Wounds are an easy entry point for insects and decay fungi.

Trees also undergo severe stress trying to wall off the wounds and compensate for the loss, depleting their nutrient reserves. New shoots that form (called epicormic shoots) have weak attachment points with high likelihood of failure (breaking and falling) in high winds, heavy snow and icy conditions. The tree itself also has a greater risk of failure if it has become infested with insects and decay fungi.

Trees that have been topped may be damaged beyond remediation. Consult with a professional arborist (one that is certified by the Kansas Arborists Association or the International Society of Arboriculture) to determine if selective pruning is an option. If the tree was topped because it was too large for the site, consider removal and replacement with a more suitable species.

The better way to prune trees is to always remove limbs back to another lateral branch or to their point of origin. Ideally, the limb being removed should be less than one-third the diameter of the limb that remains. Although this may still create large wounds in large trees, the tree should be able to recover more quickly and remaining branches will be stronger. Again, a certified arborist can help.

There are formal pruning techniques that are sometimes performed on small trees or in formal landscapes to achieve a specific result. Although some of them, especially pollarding, may look a bit like topping, it is a different process with a different result. Pleaching, espalier and other techniques are also used to control size and shape of trees in some settings.

— Jennifer Smith is a former horticulture extension agent for K-State Research and Extension and horticulturist for Lawrence Parks and Recreation. She is the host of “The Garden Show” and has been a gardener since childhood. Send your gardening questions and feedback to Lawrence Living@ljworld.com.

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