Pruning is done for a variety of reasons. Most pruning is aimed at improving structure and safety, or for controlling size. Other objectives can be to open vistas, repair storm damage, and provide clearance for structures and traffic. Good pruning includes removal of diseased, dying, or dead branches, crossing or rubbing branches, branches with thorns below eye level, sucker growth from rootstock, water sprouts from limbs, and other objectionable growth.
Pruning cuts should always be made near the base of a branch (Figure 1). Do not leave a stub. When heading back (drop-crotching) a tree to reduce its size, always cut the leader back to a lateral branch large enough to assume the terminal role. The lateral branch will eventually become the new leader. Indiscriminately sawing-off large branches (topping) is not acceptable. The new branches produced on the stubs are very weak.
The best time to prune is between mid-February and early May. Trees pruned at this time in early spring develop a callous around the cut much more rapidly than those pruned at other times. However, there are a few exceptions to this rule.
- Maples, walnuts, birches, beeches, hornbeams, and yellowwood are known as “bleeders”. The “bleeding” may be unsightly, but it does not harm the tree. Bleeding results from copious sap flow, and can be avoided by delaying pruning until after the foliage has fully emerged.
- Spring flowering trees should be pruned after flowers have dropped.
- To avoid the introduction of disease pathogens to oaks and elms, avoid pruning between April 15 and October 15.
- Prompt pruning of storm-damaged limbs and dead branches should be done to encourage wound closure and avoid potential hazards.