Tree Pruning Guide
Pruning is a necessary maintenance procedure to upkeep the structure and aesthetics of urban trees, especially when they’re young. There are several pruning techniques, all of which are used to address a unique issue or to achieve a certain outcome. Before pruning your tree, read up on some important considerations and be familiar with tree anatomy, because a wrong cut could potentially create problems for your tree rather than solve them. No need to fear -- use the following guide to make sure your tree is pruned correctly and will continue to grow into a beautiful, structurally-sound adult! Note: the following guide is for small and/or young trees. Large trees should be pruned by professional arborists to minimize safety concerns.
Why should you prune your young tree?
Formative pruning while your tree is young will save you from weak branches, poor form, and the need for corrective pruning when the tree reaches maturity. It’s a sound investment to make now rather than waiting and having to fix costly problems in the future. Tree pruning sounds like a tedious job, but the time spent doing so will reap great benefits for you and your tree!
Keeping up with pruning on a regular basis will allow you to control the size of your tree and shape it into a healthy adult that is structurally sound, aesthetically pleasing, and long-lived. Improper or lack of pruning in a tree’s formative years can cause susceptibility to rotting, growth irregularities, and vulnerability to storm damage.
Pruning is a risk-management technique. Being proactive while the tree is still young is a preventative measure to ensure weak branches don’t drop and cause property or utility damage as the tree gets larger and branches heavier.
What are some reasons for pruning your young tree?
Removing dead, dying, diseased, and rubbing branches: Removing these branches at an early stage can prevent them from falling later and can help prevent the spread of disease to the rest of the tree. Pruning these branches away rather than waiting for them to fall will allow a clean cut that will seal properly.
Removing stress-induced branches: Sucker and water sprouts will form in response to tree stress. These branches and sprouts divert energy away from the main tree trunk and canopy and need to be removed before they become too large.
Preventing co-dominant leaders: Most structurally-sound trees have a single, central trunk leader. Co-dominant trunks occur when two or more stems of a near equal size grow at an acute angle, which can cause rotting when moisture gets trapped between them. Reducing the size of a co-dominant branch or removing it helps encourage a single leader and prevents weak branch structure.
Controlling size and form: Proper formative pruning of a young tree gives control over the size of the tree and its form, which has structural and aesthetic benefits. Formative pruning influences the rate of growth, spacing of branches, and the strength of branch attachments.
What are some techniques for pruning your young tree?
Cleaning: Technique to address the issue of: dead, dying, and diseased branches. This pruning technique may be brought on by a pest invasion or storm damage and should be addressed as soon as possible.
Lifting: Removing lower branches to give more clearance over sidewalks, roads, and other infrastructure. This technique involves selecting and establishing the lowest permanent branch. For very young trees, leaving temporary branches below the lowest permanent branch can help train it and increase energy production.
Reduction: Reducing size of top branches or spread of crown for utility clearance. As opposed to topping the tree, which is a harmful pruning method that should be avoided at all costs, this method removes smaller, terminal stems from secondary branches. No more than 25% of the crown should be removed.
Thinning: Thinning the tree canopy is often done to promote growth of interior foliage by allowing more light through. This pruning method can also allow more wind to move through the canopy, which can make a tree more stable in a storm event and prevent branches from weakening. For this technique, only small live branches should be removed to avoid over-thinning -- remember the 25% rule. Avoid removing too many inner branches that may leave the ends of branches heavy with leaves, which can weaken them.
Tree Pruning Materials & PPE Checklist
Before pruning your tree, it's important to have the right tools and protective equipment for effective pruning and injury protection measures. See the checklist below to make sure you have everything you need!
For trimming thinner stems or branches
To protect your hands when using sharp tools and to reduce risk of injury when pruning
For trimming thicker stems or branches
To protect your eyes from falling tree matter
To protect your head from falling tree matter
To protect your feet from falling tree matter
Additionally, if you're going to be pruning several trees and especially if you're removing diseased branches, it's crucial to disinfect your pruning tools in between trees. This will prevent the spread of pests, diseases, and pathogens. Consider carefully and safely sterilizing your tools with bleach or isopropyl alcohol.
Tree Anatomy and Pruning Cuts
Important: The tree collar of a limb or branch should always be preserved when pruning. Never remove a branch all the way back to where the branch meets the trunk if a branch collar is present (note: reduction cuts won’t have a branch collar to cut back to). Leaving the branch collar will encourage the tree to seal the wound, because this is where a tree stores cells that create callus tissue. This is called compartmentalization.
Reduction vs. Removal Cuts:
In a reduction cut, the remaining secondary branch should be at least a third of the diameter of the removed leader branch/limb. The cut should intersect with the top of the branch bark ridge of the branch collar, and should be at a 45 degree angle.
In a removal cut, the branch or limb is removed at the point of its origin. Ensure the cut is clean and is free of jagged edges and bark peeling, and is made just outside of the bark ridge to avoid leaving a stub.
When is the best time to prune?
To maximize new growth in the spring, prune in the winter (best option for most tree species). The dormant season is the most common time of year to prune young trees. Pruning when there are no leaves present on the tree can give better visibility to the branch structure and pruning needs, too. Additionally, winter pruning reduces risk of decay, pests, and diseases.
For early-blooming flowering trees and shrubs, prune in late spring post-bloom. Pruning tree species that flower in early spring before they bloom will decrease the number of potential buds. Flowering trees that bloom in summer can be pruned in the winter.
An exception: Light corrective pruning or removal of broken/hazardous branches can be performed any time of the year. However, fall pruning should try to be avoided because of fast spreading fungal growth.
How often should you prune?
Young trees should be pruned every 2-3 years. Pruning trees in their early years is crucial for establishing the strength and form that will encourage a healthy adult tree. Establishing well-formed, well-spaced primary (or scaffolding) branches on a young tree will determine the framework of a mature tree. A proper, maintained structure will require less corrective pruning as the tree ages.
Mature trees should be pruned every 3-5 years. Pruning of large, mature trees generally should be left to professional arborists.