Pruning Trees - Guidelines

To encourage the development of a strong, healthy tree, consider the following guidelines when pruning.

General

Prune first for safety, next for health, and finally for aesthetics.
Never prune trees that are touching or near utility lines; instead consult your local utility company.
Avoid pruning trees when you might increase susceptibility to important pests (e.g. in areas where oak wilt exists, avoid pruning oaks in the spring and early summer; prune trees susceptible to fireblight only during the dormant season).
Use the following decision guide for size of branches to be removed:
1. under 5 cm diameter - go ahead,
2. between 5 and 10 cm diameter - think twice, and
3. greater than 10 cm diameter - have a good reason.

Crown Thinning

Assess how a tree will be pruned from the top down.
Favor branches with strong, U- shaped angles of attachment. Remove branches with weak, V-shaped angles of attachment and/or included bark.
Ideally, lateral branches should be evenly spaced on the main stem of young trees.
Remove any branches that rub or cross another branch.
Make sure that lateral branches are no more than one-half to three-quarters of the diameter of the stem to discourage the development of co-dominant stems.
Do not remove more than one- quarter of the living crown of a tree at one time. If it is necessary to remove more, do it over successive years.

Crown Raising

Always maintain live branches on at least two-thirds of a tree's total height. Removing too many lower branches will hinder the development of a strong stem.
Remove basal sprouts and vigorous epicormic sprouts.

Crown Reduction

Use crown reduction pruning only when absolutely necessary. Make the pruning cut at a lateral branch that is at least one-third the diameter of the stem to be removed.
If it is necessary to remove more than half of the foliage from a branch, remove the entire branch.