Trained trees will be structurally stronger and therefore less likely to break apart. Untrained trees have poor branch structure that gets worse as the limbs grow larger. Trained trees are also easier and less costly to maintain. Fixing the structural problems of a large tree is more difficult and more expensive – and sometimes impossible. Trained trees are more attractive and live longer. Poor growth patterns cannot always be corrected on an older tree and the resulting pruning will be more noticeable. Poor structure can lead to tree failure even in healthy trees.
Principles of pruning
The tips of the branches, twigs, and roots produce growth regulators that manage growth patterns. Trees also store food close to where it will be used for new growth. Pruning changes growth patterns and reduces resource availability, thus stressing the tree. Leaves produce food for the tree through photosynthesis. Pruning more than one-third of the foliage or topping decreases food production drastically and may cause stem and root areas to die. Every pruning cut is a wound, so don’t prune unnecessarily. Every cut should have a purpose. Make the smallest cut possible to achieve your purpose.
How to train young trees
Remove broken, diseased, dying or dead branches when the tree is planted. Delay any further pruning until the newly planted tree has been growing for one season. Select a leader and remove any competing leaders. A leader should be the strongest and most vertical stem. Select the lowest permanent branch. This will depend on the location and purpose of the tree. Look for a vigorous branch with a strong attachment and a stem diameter less than half the trunk diameter where the branch is attached.
Starting above the lowest permanent branch, remove any branches that have a sharp angle of attachment (including bark). Select scaffold branches in a radial pattern around the trunk, each 12-15 inches above the next. Branch diameter should again be less than half the trunk at the point of attachment. Remove branches within 4 inches of the selected scaffolding if they are of a similar size. Leave smaller diameter branches as temporaries. Select temporary branches below the lowest permanent branch. Remove only those branches that have a diameter greater than one-third the diameter of the trunk at the attachment point. Shorten the length of the temporaries to two to four buds.
When to prune
The ideal time for pruning is during the winter and early spring when the trees are dormant. It is easier to see the structure of a deciduous tree when there are no leaves. Dead, diseased or damaged limbs may be removed at any time.