To encourage the development of a strong, healthy tree, consider the following guidelines when pruning.
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:
- under 5 cm diameter - go ahead,
- between 5 and 10 cm diameter - think twice, and
- greater than 10 cm diameter - have a good reason.
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.
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.
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.
Branch Axil: the angle formed where a branch joins another branch or stem of a woody plant.
Branch Bark Ridge: a ridge of bark that forms in a branch crotch and partially around the stem resulting from the growth of the stem and branch tissues against one another.
Branch Collar: a "shoulder" or bulge formed at the base of a branch by the annual production of overlapping layers of branch and stem tissues.
Crown Raising: a method of pruning to provide clearance for pedestrians, vehicles, buildings, lines of sight, and vistas by removing lower branches.
Crown Reduction Pruning: a method of pruning used to reduce the height of a tree. Branches are cut back to laterals that are at least one-third the diameter of the limb being removed.
Crown Thinning: a method of pruning to increase light penetration and air movement through the crown of a tree by selective removal of branches.
Callus: see woundwood.
Decurrent: a major tree form resulting from weak apical control. Trees with this form have several to many lateral branches that compete with the central stem for dominance resulting in a spherical or globose crown. Most hardwood trees have decurrent forms.
Epicormic Sprout: a shoot that arises from latent or adventitious buds; also known as water sprouts that occur on stems and branches and suckers that are produced from the base of trees. In older wood, epicormic shoots often result from severe defoliation or radical pruning.
Excurrent: a major tree form resulting from strong apical control. Trees with this form have a strong central stem and pyramidal shape. Lateral branches rarely compete for dominance. Most conifers and a few hardwoods, such as sweetgum and tuliptree, have excurrent forms.
Flush Cuts: pruning cuts that originate inside the branch bark ridge or the branch collar, causing unnecessary injury to stem tissues.
Included Bark: bark enclosed between branches with narrow angles of attachment, forming a wedge between the branches.
Pollarding: the annual removal of all of the previous year's growth, resulting in a flush of slender shoots and branches each spring.
Stub Cuts: pruning cuts made too far outside the branch bark ridge or branch collar, that leave branch tissue attached to the stem.
Tipping: a poor maintenance practice used to control the size of tree crowns; involves the cutting of branches at right angles leaving long stubs.
Topping: a poor maintenance practice often used to control the size of trees; involves the indiscriminate cutting of branches and stems at right angles leaving long stubs. Synonyms include rounding-over, heading-back, dehorning, capping and hat-racking. Topping is often improperly referred to as pollarding.
Topiary: the pruning and training of a plant into a desired geometric or animal shape.
Woundwood: lignified, differentiated tissues produced on woody plants as a response to wounding (also known as callus tissue).