Let it grow: Formative structural pruning guidelines
Most people find the concept of removing multiple leaders and removing poorly attached branches to be pretty easy to understand.
The process of visualizing future growth and selecting appropriate branches for permanent scaffold or side branches is much more complex. One must also understand when temporary scaffold branches should be removed.
The first step is to understand and remember that a branch never gets any higher from the ground than where it originated. This means that if a branch on a young tree is five feet from the ground it will be at five feet for the life of the tree. This is because the trunk never elongates. All height growth occurs at the ends of the branches and new canopy branches develop from the latter or side buds higher in the tree.
Most shade trees in residential yards should have their first branch 10 to 12 feet from the ground. If they are near a building or a road, the first branches might need to be much higher. This means that over time every branch below 10 to 12 feet needs to be pruned off the tree. This is done by selectively removing the largest branches each year so one always minimizes the size of the wounds. It is best if branches are removed before they reach approximately 2 inches in diameter.
Another important guideline is that a branch being removed should be less than half the diameter of the trunk where it attaches. If a branch is proportionately too large, we prune it back to a lateral branch to reduce foliage and growth capacity. This stunts the branch and the trunk continues at the normal growth rate. Over time, the trunk will become proportionately larger than the branch and the branch can be removed.
Now in the permanent canopy, which in this case is higher than 10 feet, branches with good attachment and distribution should be saved as permanent scaffolds. Poorly attached and poorly spaced branches are removed over a period of time. This work should definitely be left to a trained arborist who is equipped with proper safety gear to work at heights. Never attempt to work trees from a ladder without an appropriate climbing saddle, ropes and helmet combined with training on how to properly use them.
Additional pruning rules that are very important to understand include:
• Always make appropriate target cuts that leave the branch collar intact with the trunk. Never flush cut.
• Do not remove more that 25 percent of the live canopy during growing season.
• Whenever possible retain branches on the upper two-thirds of the tree.
Pruning young trees is an extremely important landscape maintenance practice that is usually overlooked by homeowners. Failure to follow proper pruning practices on young trees is one of the leading causes of premature failure and often results in costly corrective work on mature trees.
Visit the following websites for more information on structural pruning of young trees. Ed Gilman from the University of Florida has an excellent guide to pruning young trees .
My article published on March 10 introduced the concept of structural pruning for young trees. The first two steps in the process of training a tree to a central leader and removing poorly attached branches were covered there .
This is a continuation of that article and will discuss how to select permanent scaffold branches off the main trunk.