Late winter: the main window
From about February into early spring, most deciduous trees are dormant. With the leaves gone, it is easy to see crossing branches, weak forks and deadwood. Insects and fungi are inactive, so fresh cuts are less likely to be infected, and the tree starts sealing them within weeks once it wakes up. Frozen ground also means less damage to your lawn and beds.
The exceptions
Some trees need different timing:
- Oak: prune only in the dormant season, never April to July. Oak wilt, a fatal disease spread by beetles drawn to fresh wounds, has been confirmed in Ontario.
- Maple and birch: they bleed sap heavily when cut in late winter. It looks alarming but is harmless to a healthy tree; if you would rather not see it, wait until the leaves are fully out.
- Spring-flowering trees and shrubs (lilac, crabapple, magnolia, serviceberry): right after they finish flowering, because they set next year's buds over the summer.
- Dead, broken or hanging branches: any time of year. Season does not matter once a branch is a hazard.
When to avoid pruning
The least good times are when leaves are coming out in spring, when the tree has spent its reserves and bark tears easily, and during leaf drop in autumn, when fungi are spreading spores. Avoid heavy pruning during a drought, too: a stressed tree copes badly with losing leaf area.
How much to take
Less than people expect. A good rule is to remove no more than about a quarter of the living crown in a year, cut back to a branch or the trunk collar rather than leaving stubs, and never top a tree: topping causes weak, fast regrowth and decay that shortens the tree's life. Deadwood, crossing branches and weak forks come first.
Permits and City trees
Under Ottawa's Tree Protection By-law, pruning that maintains a tree's health and follows good arboricultural practice needs no permit. Heavy cuts, topping or root damage can still count as injuring a protected tree. A tree on the City boulevard belongs to the City: report problems to 3-1-1 rather than pruning it yourself.
Bisson Services prunes trees of every size across Orleans and Ottawa. See tree pruning, or call (613) 558-4806 for a free estimate.
