Now that cooler weather prevails, and the storms of summer give way to clearer skies, we have time to consider how to direct next year’s growth and prevent some of the common pruning mistakes that can cause real problems down the road.
Take, as example, an oak tree- an icon if there ever was one- just past the half-century mark and with a well-established root system. The last thing you want to do to maintain this noble specimen is cut major limbs too close to the stem. Mature oaks take longer to recover from cutting back to that extent and become vulnerable to a host of complications such as splitting, decay, and even crotch rot.
The time to prune is during young and vigorous growth. By the time an oak reaches this size, it may have limbs that are more than half the diameter of the stem that will need to be cabled or bolted to prevent weak joints, disease, and major breakage during times of stress.
This is not to say that nothing can be done to enhance the growth and form of a tree of this age and size. It’s easy to identify the dead wood, but after that it takes a careful eye to determine where to lighten the crown while maintaining enough foliage on the branches to capture enough light to sustain the entire tree.
It is easier to shed underproductive limbs in the earlier stages of growth. An oak growing in a forested setting and in competition with other trees will direct its energy upwards toward the light while shedding those lower branches that are shaded out by its competitors. The stem always demands a contribution from the limbs it supports, but without sufficient canopy it becomes weak and vulnerable. A healthy oak tree has both a strong trunk and numerous, healthy branches.
After about ten years of growth, a tree starts to develop the major limbs it will retain at maturity. If you don’t want to retain the limb later on, the time to prune it is when the tree is young. Just as important at this vulnerable stage is to identify which qualities the tree possesses at this stage that will be essential to its form and identity later one and manage growth to retain these key attributes.
Now, imagine the oak in our example was planted in a landscaped setting. Its trunk thickened early as it reached in all directions to absorb the light. It may have even developed co-dominant leaders along the way and a tendency toward multiple stems. Luckily, oaks are less prone to co-dominance than other species. If this were an unpruned maple, there would be leaders shooting off all over the place. Still, it is vital never to remove more than 1/3 of the live crown in a single pruning, and in a tree of this age and maturity any pruning should be much more conservative and spread out over time.
Whenever pruning is necessary, think of it as surgery rather than logging. You want sharp tools designed for this kind of work, not a broad ax. Leaving branch stubs, living or dead, weakens the tree and increases the risk of rot and parasites. It is best to prune in the dormant season when it causes less stress to the tree. And for goodness sake, don’t paint over the wounds. It just makes the tree more susceptible to disease and decay.
Finally, use proper precaution when going out on a limb to prune a large tree. Always have an anchor, and a trusted partner on belay. With care and forethought, you will be enjoying the shade of your tree for many years to come.