How to prune a young tree so it does not split later

The short version

The first years of a tree's life are when pruning does the most good for the least effort.

Aim for one strong central leader and well-spaced permanent branches.

Keep some low branches for now. They feed the trunk and can come off later.

Make small cuts, just outside the branch collar, while the tree is dormant. The month-by-month exceptions are in when to prune trees in Ontario.

Never top a young tree to keep it small. Choose the right species for the space instead. That argument is in why not to top a tree.

Why do the first years matter so much?

A young tree is still establishing its permanent architecture, and its responses to small corrections are vigorous. When you remove a small branch, the tree seals a small wound and reallocates that growth elsewhere. Wait twenty years and the same correction means a large cut, a large wound, and more opportunity for decay. The International Society of Arboriculture's homeowner guidance stresses this early training for exactly that reason (ISA, Pruning Young Trees), and university extension guidance from a similar northern climate describes pruning in the formative years as the best preventive maintenance a young tree can receive (University of Minnesota Extension, Pruning trees and shrubs).

The wider picture, including mature trees, is the Durham pruning guide.

Step 1: Choose one central leader

A central leader is the single dominant upright stem that continues the trunk upward. Most shade trees in our area, such as maples, lindens and oaks, grow strongest with one leader. A codominant union is the junction formed when two upright stems of similar diameter compete for the top of the tree. As both thicken, bark becomes trapped between them and the joint becomes mechanically weak.

Stand back and identify the straightest, strongest upright stem. That is your leader. Look for any rival stem of similar size. Remove the rival entirely, or shorten it to a lateral branch so it stops competing with the designated leader.

If you are unsure which stem to keep, choose the one positioned most directly above the trunk, because it usually carries the most vigorous terminal growth.

Step 2: Pick the permanent scaffold branches

Scaffold branches are the main limbs the tree will carry for life. Good ones are clearly smaller in diameter than the trunk where they attach. They leave the trunk at a wide, open angle rather than a tight V. They are spaced out vertically and around the trunk, not bunched at one height. They sit above the clearance height you will eventually need over a lawn, path or driveway.

You do not need to choose them all in one year. Mark the obvious keepers now and revisit the remaining candidates next winter, when the structure is easier to judge.

Step 3: Leave temporary lower branches for now

Crown raising is the gradual removal of lower limbs to create clearance, and on a young tree it should happen slowly rather than all at once. It is tempting to strip the lower trunk bare, but small lower branches feed the trunk and help it develop thickness and taper. Shorten any that interfere with mowing, and remove them gradually over several years as the canopy rises. This is the slow version of crown raising described in the full pruning guide.

Step 4: Remove the problem branches

Each winter, look for dead or broken branches. They are an entry point for decay. Remove them back to live wood or the collar.

Crossing or rubbing branches wound the bark where they wear. Keep the better placed branch and remove the other.

Tight V-shaped unions trap bark and weaken the joint. Remove or shorten the weaker stem.

Branches growing back into the canopy crowd and rub. Remove them at the point of origin.

Suckers from the base steal energy and spoil the form. Cut them at the base. If a removed tree keeps sending them up, the stump usually needs grinding, which is a different job from pruning a tree you are keeping.

Step 5: Make the right cut

A correct cut is made just outside the branch collar, the slightly swollen ring where the branch meets the trunk. Do not cut flush to the trunk, and do not leave a stub. For any branch heavy enough to tear bark as it falls, use three cuts.

First, a small undercut a short distance out from the trunk. Second, a top cut a little further out, which removes the weight. Third, the final cut just outside the collar.

Extension guidance describes the same sequence for large limbs: an undercut first so the bark does not tear, then a relief cut further out, then the final cut that leaves the collar intact (University of Minnesota Extension, Pruning trees and shrubs). Use clean, sharp hand pruners or a pruning saw appropriate to the branch diameter.

When to do it

For most young deciduous trees, late winter while the tree is dormant is ideal. The structure is easy to see without leaves. Species exceptions are in when to prune trees in Ontario. Check for nesting birds before cutting in spring or summer (Canada.ca, General nesting periods of migratory birds).

What not to do

Do not top the tree to keep it small. Topping causes weak regrowth and decay (ISA, Why Topping Hurts Trees). If the species will outgrow the spot, that is a planting question, not a pruning one. More on this: why you should not top a tree.

Do not over-prune in one year. Remove a modest amount each winter and let the tree respond before making additional structural corrections.

Do not prune a newly planted tree heavily. Beyond dead or broken branches, let it settle in first.

A simple yearly routine

Once each winter, for each young tree, ask five questions. Is there still one clear leader? Any dead, broken, crossing or rubbing branches? Any new tight V unions forming? Do lower temporary branches need shortening or removing? Is anything growing toward the house, a path or a line?

Ten minutes a year, for the first several years, is probably the most economical tree maintenance a homeowner can provide.

When to call us

Call a professional if the tree is already too tall to reach from the ground, if a codominant split is already large, or if branches are near power lines. We are happy to do a single structural visit and show you what to watch for afterward. Call or text (289) 675-8777, or see our tree trimming and pruning service and the tree pruning guide for Durham Region. Company background is on the about page.

Sources

International Society of Arboriculture, Pruning Young Trees, Why Topping Hurts Trees, and Pruning Mature Trees.

University of Minnesota Extension, Pruning trees and shrubs.

Government of Canada, General nesting periods of migratory birds.