Pruning

What and when to prune

pruning a shrub

Early spring is a good time to assess recently planted trees, and to prune out broken branches or to start training them.

You’ll want to avoid full pruning during spring  from bud break through leaf expansion, or during the period of leaf color change in the fall. A tree is going through major changes during these times, and branch removal can reduce the vigor of the tree.

When pruning recently planted trees, wait until the tree has been in the ground for about two years as it will have begun to adjust to its new location and to establish a healthy root system. This is the time to begin the crucial training of your tree so it grows into a beautiful, healthy and safe tree for everyone in the community to enjoy for many years to come.

Early spring

  • Summer-flowering trees and shrubs. 
  • Evergreen or deciduous shrubs. 
  • Non-blooming broadleaf evergreens. 
  • Hybrid tea, floribunda, grandiflora and miniature roses. 
  • Winter-kill removal from climbing

Late spring / early summer

  • Spring-flowering shrubs immediately after their blossoms fade so pruning is complete before flowers are set for the following year. 
  • Half of new elongating shoots on pines and other needled evergreens.

Summer

  • Deciduous or evergreen shrubs.
  • Mature (2-3+ years old) climbing and rambling roses after they bloom.
  • Dogwoods, maples, walnuts, birches, elms, yellowwood if needed.
  • Summer-flowering shrubs and trees as blossoms fade.

Fall

  • Long rose canes. 
  • Thin plants once they are dormant.

Winter

  • Berry shrubs or trees. 
  • In late winter or very early spring, before the sap is running, prune deciduous trees, fruit trees and deciduous shrubs that are not spring bloomers (make sure temperatures are above -7 degrees celcius / 20 degrees fahrenheit

Pruning methods

Thinning

A lateral stem (side branch) or limb is cut all the way back to a main branch or the trunk. This encourages growth of remaining branches and opens the plant interior to keep internal branches healthy. Selective thinning can keep a plant the same width and height for years.

Shearing

All stems are shortened by a certain amount to maintain shape of a hedge or topiary. It must be repeated often and should not be used for most shrubs or trees. Vigorous growth occurs just below the pruning cut and can lead to a dense outer shell that blocks light from reaching the inside, damaging the internal branches.

Heading

The terminal bud is removed by cutting anywhere along the main stem. Growth begins below the cut and results in new stems or clustered branches that can create a crowded interior.

Lateral pruning (“heading back”)

Another form of heading where the main stem is cut back to a lateral branch. The response
to this cut is similar to thinning and will not cause growth below it on the main stem,
but will encourage branching growth from the cut point and a denser canopy overall.

Pruning tips

  • Cut on an angle, 5 millimetres above a bud.
  • Cut towards, not away from the bud.
  • Avoid rough cuts as bruised tissue is slow to heal

Training young trees

Limit pruning of newly planted trees to the removal of dead and broken branches, or the correction of multiple leaders.

Tips to keep in mind when pruning young trees:

  • Know the general growth habit of a tree before beginning.
  • Leave the temporary lower branches on the tree until they reach 2.5 cm in diameter in order to increase trunk growth and root development.
  • Avoid removing lower branches too quickly; keeping lower branches longer allows for larger and stronger tree trunks.
  • Concentrate efforts on removing any crossing, rubbing, broken, diseased and/or weak-angled branches in the upper portion of the tree.
  • Develop one main leader on shade tree species such as oak, maple, ash or linden.
  • Concentrate efforts on removing rubbing and competing branches on species such as crabapple and other fruit trees.
  • Space permanent branches 38–76 cm (15–35 inches) apart.
  • Remember developmental pruning is an ongoing process over the first 15–20 years of a tree’s life.

Take a moment to check out your tree and the way it’s growing. Start by looking at the tree’s trunk; this is also known as the tree’s main leader. A tree with one main leader tends to be much stronger than one without. Training your tree to have one leader when it is young will ensure a strong and safe tree as it matures.

Diagram shows a side branch longer than centre branch or trunk

Unsafe: notice the branch at the top that is competing with the main leader.

Diagram shows trunk splitting into two symmetrical branches of even length

Safe: the leader has split into two leaders, this is safe as long as there is a U–shape between the two leaders

Diagram shows trunk as main branch leader, longer than others

Safest: the main leader is the dominant branch

Diagram shows trunk with branches growing at different angles

Branches extending from the trunk or main leader at sharp V–shaped angles are weak and prone to breakage; U–shaped angles are stronger.