When a tree branch is removed, rapid, vigorous regrowth often follows. This is a natural biological response by the tree to injury or changes in its internal balance. This unwanted growth, appearing as vertical “watersprouts” on the branches or “suckers” from the base or roots, is the tree’s attempt to quickly replace lost foliage and energy production. Understanding this reaction is the first step toward preventing its recurrence.
The Biology of Unwanted Regrowth
A tree’s growth is regulated by a delicate balance of plant hormones, primarily through apical dominance. The growing tip of a branch produces auxin, which travels downward and suppresses the growth of dormant buds located lower on the stem. This ensures the tree focuses its energy on upward and outward growth.
When a branch is removed, the source of auxin is eliminated, disrupting hormonal control. The decrease in auxin concentration allows another class of hormones, particularly cytokinins, to activate the previously dormant buds. These activated buds rapidly shoot out as watersprouts. Suckers operate under a similar principle, typically arising from dormant buds on the root system or the root crown in response to canopy removal or stress.
Strategic Pruning Cuts to Minimize Recurrence
The most effective way to limit unwanted regrowth is to use precise cutting techniques that encourage the tree’s natural healing process. The goal is to make a “collar cut,” which removes the branch without damaging the branch collar—the slightly swollen ring of tissue where the branch meets the trunk or a larger limb. This collar contains specialized cells that seal the wound through a process called compartmentalization of decay in trees (CODIT).
Cutting just outside this collar preserves the tree’s natural defense zone, allowing it to quickly form a protective callus over the wound. This rapid sealing minimizes the entry point for decay and reduces the stress response that triggers vigorous watersprout development. A common mistake is a “flush cut,” which removes the collar entirely, leaving a large, slow-healing wound that stresses the tree and encourages prolific sprouting.
Another error is leaving a stub, which prevents the collar from sealing the wound and acts as a site for decay organisms to enter the main trunk. For larger branches, the “three-cut method” is advised to prevent the weight of the falling limb from tearing the bark down the trunk. The first two cuts are made further out on the branch to remove the bulk of the weight, and the third cut is the precise collar cut.
Using sharp, clean tools is equally important, as a smooth cut heals far faster than a jagged one, further reducing the tree’s stress. By respecting the branch collar, the pruning wound heals efficiently, negating the need for an emergency flush of watersprouts.
Chemical Suppression Methods
While proper pruning is the primary preventive measure, chemical methods can be employed for persistent regrowth issues, particularly with suckers or when removing stumps. These methods are reserved for situations where mechanical removal is impractical or insufficient. Chemical treatments fall into two main categories: plant growth regulators and herbicides.
Plant Growth Regulators (PGRs)
PGRs containing a synthetic auxin, such as Naphthaleneacetic acid (NAA), are used on freshly cut surfaces, especially for species known to sucker heavily. Applied immediately after a cut, the synthetic auxin mimics the natural hormone, signaling to dormant buds that apical dominance is still intact, inhibiting sprout development. This method focuses on prevention rather than killing existing growth.
Herbicides
Herbicides, often called stump killers, prevent root system resprouting after a tree is cut down. Products containing active ingredients like glyphosate or triclopyr are applied directly to the fresh cut surface, targeting the living tissue just beneath the bark (the cambium layer and sapwood). For treatment to be effective, it must be applied within minutes of the cut, as the tree rapidly seals off the vascular tissue, preventing the chemical from translocating to the roots.
It is necessary to follow all label directions, as improper application can cause non-target damage to surrounding plants through root grafts or runoff. Chemical suppression should be used selectively and with caution, never as a substitute for making the correct, clean pruning cut.