Last week I wrote about the perils of topping trees. I discussed how it stresses the tree, causes decay, encourages long-term hazardous growth, can sunburn the fragile vascular system and creates an all-around ugly tree. Sometimes, however, a tree must be reduced in height or spread to provide clearance for utility lines, to create a sunny garden patch or to allow solar collectors to do their job. Fortunately, there are recommended techniques for doing this. Here is what you need to know about bringing an oversized tree back down to size.
Good tree growth and training start the day the tree is planted. Some trees need a light pruning to thin the tree canopy and remove crossing branches that rub one another. More moderate pruning requires heading back to remove portions of limbs that may extend too far or are in the way when working around the tree. Major pruning can remove a co-dominant leader or a branch that is competing to be the leader, as well as limbs that hang too low or create an out-of-balance tree canopy.
As the tree matures, there will come a time when major structural pruning will be required. And the best alternative to topping is called "drop-crotching." When performed correctly, drop-crotching is like a good haircut - virtually harmless but noticeably appealing.
Drop-crotching is a technique that combines branch-thinning with height and spread reduction. Instead of simply lopping off the ends of branches, limbs forming the perimeter of the tree are pruned at their junction with shorter, large-diameter-side branches. The rule of thumb is to cut back to a lateral branch that is at least one-third the diameter of the limb being removed. Often times this can be accomplished without cutting limbs larger than 6 inches in diameter.
And with the presence of a leader, latent buds do not sprout into the bushy growth that results from cutting off branch ends. With a skilled arborist, drop-crotching can safely reduce tree size yet retain the natural tree form.
The secret to good pruning is leaving the branch collar. The branch collar is the swollen area between the tree trunk and the branch you are removing. This area of tissue is fast-growing and heals quickly.