Here are some guidelines to follow when pruning deciduous trees. The tools needed to properly prune trees are a pair of sharp bypass pruners (also called secateurs), a pair of loppers for thicker branches, and a pruning saw for larger branches. Tools should be sharp to prevent ragged cuts.
The ideal time to prune trees is in late winter when trees are dormant, before buds begin swelling in the spring. This is particularly important for trees which are prone to attack from insects and disease such as elm, ash, oak and fruit trees. Generally speaking, November to March are the safe pruning months for disease-prone trees. Dead branches can be removed in any season. Trees which run sap in the spring, such as maples, are better pruned in late winter, or after June 1st. Pruning trees in the fall can stimulate new growth which will not have time to harden off before winter and can result in subsequent winter dieback. Trees which flower early in spring, such as magnolias and lilacs, can be pruned following flowering.
When pruning, branches should be cut just beyond the natural swelling at the base of the branch (the branch collar on graphic). Never cut into this swollen area, as such cuts will prevent the wound from healing properly. Equally important, never leave a stub, as this can later be an entry point for disease. For larger branches a three-part cut (see graphic below) will prevent a heavy branch from ripping the bark further down the tree and will also prevent injury to the person doing the pruning.
If you are pruning two V-shaped branches, never cut into the raised bark ridge which runs between the two branches (see graphic above). Branches larger than 13 cm in diameter should not be removed at the main trunk, but rather cut back further up the branch where the diameter is smaller. Cuts over 13 cm in diameter run the risk of never healing properly.
Ideal targets for pruning removal are crossing or rubbing branches, closely spaced branches, dead branches and suckers. An ideally pruned tree will have branches spaced around the tree similar to the steps on a spiral staircase. This goal is much more achievable with young trees where pruning begins the year following the planting. As a rule of thumb, never remove more than 20% of the foliage mass of the tree in one season, otherwise the tree will experience undue stress and have difficulty recovering. Do not put tar or any kind of sealer over the cuts. Studies have shown that such products can harbour disease and delay healing.
If the tree is large and upper branches are high, don’t hesitate to call in an expert to do the job. To avoid damage to your trees as a result of improper pruning practises, choose tree companies with trained arborists on staff.
By Elizabeth Spedaliere, Tri-County Master Gardener
