When to prune trees in London, ON

“When should I prune?” is one of the most common tree questions. For most trees in Southwestern Ontario the answer is late winter, but there are a few important exceptions.

The short answer: late winter, for most trees

For most deciduous trees, the dormant season is the best time for routine pruning. In London that usually means from late fall, after the leaves drop, until just before the buds open in spring. Late winter is often ideal.

• You can see the structure. With the leaves off, it’s easier to spot crossing, rubbing, dead and poorly attached branches.
• Less stress on the tree. A dormant tree has its energy stored, and wounds begin to close when growth starts in spring.
• Fewer pests and diseases are active in cold weather to find fresh cuts.
• Frozen ground can mean less wear on lawns and gardens under the work.

Trees with their own timing

Oaks: not from April through July

Oak wilt has been confirmed in Ontario. It is spread in part by small sap beetles that are drawn to fresh wounds on oaks in the warm months. The standard advice is to avoid pruning or wounding oaks from April through July. If an oak must be cut in that window for safety, the work should be planned with that risk in mind.

Elms: prune while dormant

The beetles that carry Dutch elm disease are most active in spring and early summer and are attracted to freshly cut elm wood. Elms are best pruned while dormant, and elm wood shouldn’t be stored as firewood with the bark on.

Dead, broken or hanging branches don’t wait for the calendar. Safety pruning can happen any time of year.

Spring-flowering trees: prune after they bloom

Magnolias, crabapples, serviceberries and flowering cherries set their flower buds the year before. Pruning them in winter removes those buds. If flowers matter to you, prune soon after they finish blooming. For fruit trees prone to fire blight, such as pears and some crabapples, pruning in dry, dormant weather is safer.

Maples and birches that “bleed”

Maples, birches and a few others can drip sap when cut in late winter and early spring. It looks alarming but is not usually harmful. If you’d rather avoid it, these trees can be pruned once the leaves have fully expanded.

When not to wait

Some work is about safety, not timing. Dead branches, broken or hanging limbs (often called “hangers”), storm damage and branches that are touching a roof or a service line can and should be dealt with whenever they are found. Keep people and cars clear, and don’t try to remove large limbs near wires yourself.

Times to go easy

• During leaf-out in spring. A tree has spent much of its stored energy pushing out new leaves, so heavy pruning then is harder on it.
• During drought. A tree already short of water copes poorly with losing leaves and with new wounds.
• Heavy cuts in late summer and early fall. Light pruning is fine, but heavy pruning late in the season can push new growth that may not harden off before winter.

How much to take

Good pruning has a reason behind every cut: removing dead wood, improving structure, clearing a roof or path, or reducing weight on a weak limb. A common guideline is to remove no more than about a quarter of a tree’s live canopy in one year, and often much less on mature trees.

Cuts should be made just outside the branch collar, the slightly swollen area where a branch joins the trunk, so the tree can seal the wound. Wound paint isn’t needed. Topping, or cutting a tree back to stubs, should never be done: it leads to weak regrowth and decay.

Check whether a permit is needed

Some trees in London are protected, and the City of London may require a permit for work on certain trees on private property. Trees owned by the City, such as many boulevard trees, shouldn’t be pruned without the City’s permission. Before major work, check whether a permit is needed. If you’re not sure, we can help you check.

This is general information. Every tree and site is different. For advice on a specific tree, get a free quote or book a Certified Arborist Assessment.

About the author

Jason Korkidakis

Jason is Koala Tree’s Owner and Lead Arborist in London, ON. He leads an 8-person crew and assesses trees for homeowners, condo boards and property managers.

ISA Certified Arborist ON-3263ATRAQ qualifiedPPQ qualified

About Jason More Field Notes