How to Trim a Plum Tree

Plum trees are generous. They grow in most Surrey gardens, fruit reliably for years, and only ask one thing in return: don’t prune them in winter.

(If that’s news, good — you’re reading this before the damage is done. If it isn’t, you’re probably reading this after a March tidy and a very bad August.)

The answer to “when should I trim my plum tree?” is: late July through early August, here in the Lower Mainland. Not spring. Not autumn. Not January because you finally have a free Saturday. Summer — when the tree is actively growing, wounds seal fast, and the fungal spores that cause silver leaf disease are at their least active.

Quick answer: Trim plum trees in summer. Cut to an open vase shape, remove crossing branches and dead wood, and take out no more than 20–25% of the canopy in one session. Do not prune in winter or spring — silver leaf disease enters through dormant-season cuts and can kill the tree within a few seasons.

When to trim a plum tree — and why it’s backwards from everything else

Most trees get pruned in winter. Dormant season, no leaves, easy to see the structure. For apples, pears, and most ornamental trees, that’s perfectly fine.

Plum trees are different. They’re highly susceptible to silver leaf disease — a fungal infection that enters through freshly cut wood. In winter, the spores are active in the soil and air, and the tree’s natural sealing mechanism is at its slowest. That’s the worst combination you can create.

I reckon half the plum trees I’ve assessed across the Fraser Valley that looked sick or dying had a winter or early spring pruning somewhere in their history. Sometimes it was five years back. Silver leaf is patient.

The window that works: late July through early August.The tree is in active growth. Wounds callus over quickly. Spore counts are lower. The structure is visible enough to work with, and the season’s vigorous growth is obvious and easy to target.

A few weeks either side is fine. If you miss the window, wait until next summer. One skipped pruning season won’t hurt the tree. One winter prune might cost you the tree.

For a broader view on fruit tree timing generally, our guide to when to trim fruit trees in the Fraser Valley covers the other common species and where the rules differ.

How to prune a young plum tree

Young plum trees — anything planted in the last three years — need to be trained into shape before they need maintenance pruning. The goal is a structure that will work for the next twenty years, not a tidy-up job.

The target shape is an open vase or goblet: three to five main branches (scaffold branches), angled outward from the trunk at about knee to hip height, with the centre kept relatively clear. This lets light and air into the canopy, reduces disease pressure, and keeps the tree at a manageable size as it matures.

In the first summer after planting:

• Select three to five well-spaced branches emerging from the trunk at 40–60 cm off the ground
• Remove everything else back to the trunk — no stubs longer than 1 cm
• Cut the selected branches back by about a third, to an outward-facing bud

In years two and three: remove inward-growing or crossing branches, and shorten the leaders by about a quarter each season. You’re not pruning hard — you’re shaping.

Clean tools. Sharp tools. Flat cuts close to the branch collar. Do it in summer. Nothing complicated about it.

Pruning an established plum tree

Once a plum tree is five or six years old, the annual maintenance changes. You’re no longer training it — you’re keeping it productive and healthy.

What to remove each summer:

• Dead or diseased wood — cut back to healthy tissue, well behind any discolouration
• Crossing branches — two branches rubbing create a wound on both
• Water shoots — the vigorous vertical shoots that spring from old wood or below the graft union. They look strong. They’re drawing energy away from fruiting wood. Remove them at the base as soon as you see them
• Inward-growing branches — anything closing off light and airflow to the centre of the canopy

What not to remove: more than 20–25% of the canopy in a single season. Heavy pruning triggers a flush of water shoots the following year that undoes your work and then some.

A homeowner near Langley called us in after attempting to tidy a neglected 10-year-old plum tree himself — in March, effectively winter. He left stubs on three of the main limbs and created four competing leaders off the central trunk. By August, two of those limbs had the distinctive silvery sheen of silver leaf. Crown reduction and silver leaf removal ran $650. It would have been a $300 summer tidy if he’d called first. The tree survived, but it took two full seasons to look right again.

Silver leaf disease: why the timing matters this much

Silver leaf (Chondrostereum purpureum) is a fungal disease that affects plums, cherries, and other stone fruit. It gets into the tree through wounds — most commonly pruning cuts made during the dormant season when spores are active and the tree can’t seal fast enough to keep them out.

The first sign is a silvery, metallic sheen on the upper surface of leaves — usually one or two branches initially. That’s not a nutrient problem. It’s a fungal toxin travelling through the sapwood. Within one to three seasons, those branches die back. In a severe case, the infection reaches the trunk and the whole tree follows.

If you see silver leaf symptoms:identify which branches are affected, then cut back to healthy wood well behind the discolouration. Look for clean, white timber in the cross-section — any brown staining means you’re still in infected tissue. Keep cutting until you find clean wood.

Remove all affected material from the property. Don’t compost it. Don’t chip it into mulch.

A small infection on one branch, caught early, is manageable in summer with sharp tools and some patience. If multiple main scaffold branches are involved, or the staining appears when you cut into the trunk — that’s the conversation about whether the tree is worth trying to save or whether removal is the honest call. The RHS has a clear diagnostic guide to silver leaf disease if you want to confirm what you’re looking at before touching anything.

Common plum tree pruning mistakes

Pruning in winter or spring.Covered above. Don’t. (And yet here we are, having the conversation, which means someone in your neighbourhood is about to do it.)

Leaving stubs.A stub — a cut that leaves 3–4 cm of branch sticking out — doesn’t seal. The dead tissue rots back to the collar, which is exactly where you don’t want rot to establish. Cut close to the branch collar, but not into it.

Topping. Flat cuts across the top of the canopy to control height. This is sometimes called hat-racking in the trade. It doesn’t reduce the tree — it triggers dozens of weak, fast-growing shoots from just below the cut. Two seasons later the tree is larger and structurally worse. If height is the problem, crown reduction — selective removal back to lateral growth — is the technique, not topping.

Over-removing in one session. More than a third of the canopy at once stresses the tree. Spread heavy work over two or three consecutive summers.

Dull tools. A rough cut tears more tissue than a clean cut and takes longer to seal. Sharpen or replace blades before you start — this is not optional.

Applying wound sealant. Old guidance. Modern arboricultural consensus, including ISA Canada, is clear: sealants trap moisture and promote the rot they’re supposed to prevent. A clean summer cut is its own protection.

When not to call us — and when you should

Small plum tree, under about 5 metres, accessible from the ground or a short step ladder, being maintained rather than rescued: do it yourself in summer. A decent pair of loppers and sharp secateurs is all you need. You genuinely don’t need an arborist for that.

Call us when:

• The tree is above 6 metres and you’d need a ladder past shoulder height to reach the main structure
• Branches are near the house, power lines, or a shared fence
• You’re seeing silver leaf symptoms on more than one limb
• The tree hasn’t been touched in a decade and needs significant crown reduction
• You’ve already pruned and something looks wrong

Nine times out of ten, the assessment call either saves someone from a bigger mistake or confirms they were doing fine on their own. Consultation is $150 and credited against any work that follows.

What plum tree pruning costs in Surrey, BC

Nobody lists prices. We do.

Rule of thumb: annual light pruning costs half what a major crown reduction does. Keep up with the tree and you’ll spend less over ten years than if you let it go for five and then call for emergency help. That’s the boring, correct answer.