Get the pruning time wrong and you risk more than a poor harvest.
You’re opening the tree up to silver leaf disease, a fungal infection that can kill established branches. In severe cases, it can kill the whole tree.
When to Prune Plum Trees – By Professional Tree Surgeons
Mid summer pruning
In Scotland, it is best to lightly prune plum trees that are already established is mid-summer, between June and August.
Stone fruits like plums and damsons behave differently from apple and pear trees in this respect.
Apple and pear trees get pruned in winter when they’re dormant.
But for plums, winter pruning increases the risk of silver leaf. This is because fungal spores are most active in cold, damp conditions and find their way into open pruning wounds easily.
On a dry and warm day
Prune on a dry day whenever you can.
Summer pruning lets the tree seal its cuts quickly.
Wet conditions help fungal spores settle and take hold in fresh pruning wounds.
Maturity of the tree factors
The age of a plum tree matters.
Plum trees ages between one to three years should be lightly to moderately pruned in summer for formative shaping and health. If the Scottish weather is good, you may be able to push the pruning forward into spring.
Once the tree is established and ages further, pruning is even lighter. The goal of this is to remove dead of diseased branches, while encouraging airflow to healthy sections.
Tools for Pruning Your Plum Tree
Sharp, clean tools make the difference between a clean pruning cut and a ragged one that tears bark and slows healing.
For pruning your plum tree, you’ll need secateurs for shoots and smaller branches up to about 1cm (roughly 1in) diameter.
Loppers handle branches up to 3-4cm across, and pruning saws deal with anything larger.
Most domestic jobs on an established plum can be handled with secateurs or a pruning saw alone, but having loppers available for mid-sized branches makes the work faster.
You might not think to do this, but always sterilise tools between trees. Particularly if you’ve been cutting out diseased wood.
Bacterial canker and silver leaf can both travel on dirty blades.
How to Prune a Plum Tree
The general rule with pruning plums is to remove dead, diseased, and crossing branches before anything else, then work on the shape.
On a free-standing plum tree, go through the structure in this order.
Remove Dead, Diseased, and Damaged Wood
Start with any branches that are clearly dead, diseased, or damaged.
Branches affected by silver leaf disease develop a silvery sheen on the leaves, and a cross-section of infected wood shows brown staining in the centre.
Cut back to clean wood, removing at least 15cm beyond any visible staining.
Bacterial canker shows as sunken, discoloured patches on the bark with amber-coloured gum oozing from the wood.
Prune away affected branches back to healthy tissue and burn or bag the prunings.
Don’t leave a stub.
Each pruning cut should come back to the main branch or trunk, just outside the branch collar (the slightly raised ring of bark where the branch meets the parent wood). The collar is where the tree seals over a wound.
Cut through it or leave a protruding stub above it, and the wound won’t heal correctly.
Remove Crossing and Inward-Growing Branches
Branches growing into the centre of the tree reduce air circulation and block light penetration. They rub against neighbouring branches they create wounds that let disease in.
Removing crossing branches and shoots growing into the centre opens the canopy.
Better air flow and light reach the fruit.
Reducing that congestion also cuts the damp conditions that let fungal disease take hold through summer.
A well-balanced, open-centred plum tree is what you’re aiming for.
Where two branches are rubbing or crossing, remove the weaker one, or the one in the more awkward position that would be harder to work around in future years.
Shorten Side Shoots
With the structural work done, shorten side shoots back to three or four good buds.
Cut just above an outward-facing bud, pointing away from the centre of the tree rather than back toward it.
New growth follows the direction of the bud, so an outward-facing bud sends growth out into open space rather than back into the canopy.
A good pruning cut sits just above the bud, angled slightly to shed water away from it. Don’t cut so close that you damage the bud, and don’t leave a long section of shoot above the bud that will die back to a stub.
Pull Up Any Suckers
Suckers grow up from the rootstock below the graft union.
They’re not part of the plum variety you planted and they take energy away from the tree.
Pull up any suckers you find rather than cutting them at ground level. Cutting tends to stimulate more shoots from the same root.
Grip the sucker as close to its origin as you can manage and pull it sharply downward to remove it cleanly.
Thin the Fruit in Early Summer
Plum trees often set more fruit than the branches can comfortably carry.
After a warm spring, overcrowded clusters that aren’t thinned in late June tend to stay small, ripen poorly, and put enough weight on shoots to break them.
Aim for plums spaced roughly 5-8cm apart along each shoot once thinning is done.
Pruning Young Plum Trees
Young plum trees need formative pruning in the first few years to build a strong, open framework before the main fruit-bearing branches are established.
For a free-standing tree, the aim is to develop three or four main branches coming out at wide angles from a short trunk around 75cm tall.
In the first growing season, select the strongest shoots to become the main framework branches and remove everything else.
In the second and third years, the main framework branches should be pruned back by about a third to encourage branching and keep the tree correctly shaped.
Remove any shoots growing into the centre as they appear, and prune away shoots growing toward a wall or fence if the tree is planted close to one.
Don’t forget newly planted fruit trees should be mulched to ensure they have the best chances to thrive.
Cutting Back an Overgrown Plum Tree
A neglected plum tree that’s been left for several years tends to become congested in the centre.
Multiple branches cross, dead wood accumulates, and side shoots that have grown well beyond where they’re useful.
The tree may still be producing fruit, but branches breaking under the weight of a heavy crop becomes a real risk.
The weight of fruit on thin, overcrowded branches means much of what does ripen will be small.
The way to prune an overgrown plum is to spread the restoration over two or three years rather than trying to get the tree correctly shaped in a single session.
Removing too much growth at once stresses the tree and triggers a flush of vigorous, unproductive new growth the following spring.
In the first year, focus on dead, diseased, and crossing branches.
In the second year, continue opening the centre and shortening side shoots.
By the third season, the tree should be producing better fruit and be manageable on a yearly maintenance basis.
The general rule of thumb is to not remove more than a third of the tree’s total growth in a single year.
Pruning Mistakes to Avoid
Remembering when to prune
Pruning in autumn or winter is the most damaging mistake, and the one that catches most gardeners out.
Plum trees are not apple and pear trees, and carrying over the same timing increases the risk of silver leaf considerably.
Leaving stubs
Leaving stubs after cuts is a close second.
Cut back to the collar cleanly.
A stub can’t heal over, eventually dies back into the branch below it, and creates an entry point for disease in the process.
Removing too much
The way to prune a neglected plum is gradually.
Only take away a third of the problem growth at most in any single year.
Going too hard in year one triggers vigorous, unproductive regrowth that creates more work the following season.
Silver Leaf Disease
Silver leaf disease is the main reason plum trees require a different pruning schedule from other fruit trees.
The pathogen enters through pruning wounds, broken branches, and damaged bark.
As it spreads through the tree, it causes the characteristic silver sheen on the upper surface of the leaves.
But by the time the silvering is visible, the fungus may have been active in the wood for several months.
Not just a plum tree problem
All stone fruits are susceptible to silver leaf disease, including damsons, cherries, and peaches.
The risk is highest in autumn and winter when spore counts in the air are elevated and the tree can’t heal pruning wounds quickly.
Summer pruning, on a dry day with clean tools, is the most effective prevention.
Pruning wounds made in summer close over quickly. Spores have far less time to settle before the wound seals.
Silver lead disease inspection
Plum trees require close inspection each year when you prune.
If you spot the silvering on leaves, cut back into the wood and check the cross-section. Brown staining in the centre of the wood confirms active infection.
Remove all stained wood back to 15cm beyond the last visible staining, and dispose of infected material by burning it or double-bagging it.
Composting infected wood keeps the risk of silver leaf in your garden for longer.
Silver leaf has no chemical cure once it’s established in the wood.
If you’re uncertain whether a tree is infected, expert advice from a qualified arborist is worth getting before you start cutting.
Trees stay healthy through prevention.
Correct timing and clean tools are your main defences against silver leaf. Remove infected wood as soon as you spot it, and the fungus is far less likely to spread.
Frequently Asked Questions
What month can you prune a plum tree?
Established plum trees should be pruned between June and August. Early spring or mid-summer works for young trees in their formative years. Autumn and winter pruning increases the risk of silver leaf disease and should be avoided.
Can you trim the top of a plum tree?
Cutting back the top of a plum tree to limit its height is possible, but hard topping creates large open wounds, triggers vigorous unbalanced regrowth, and distorts the shape of the tree long-term. If a plum tree has grown too tall, removing the leading shoot back to a strong side branch lower down is a better approach than a flat cut across the top. For more significant height reduction, crown reduction carried out by a certified arborist is the safer option.
What branches to cut when pruning?
Remove dead, diseased, and damaged branches first. Then take out any branches that are crossing or growing into the centre of the tree. Finally, shorten side shoots to three or four good buds, cutting just above an outward-facing bud. As a general rule, branches that are growing in the wrong direction, rubbing against others, or blocking light from the centre of the canopy are the ones that should be removed.
What part of a tree should not be cut?
Don’t cut into the branch collar (the raised ring of tissue where a branch meets the trunk or a larger branch). The collar is what the tree uses to heal over a pruning wound. Cut through it and the wound can’t seal properly. Leave a protruding stub above it and the stub dies back through the collar, again preventing healing. Every pruning cut should land just outside the collar, with no stub remaining.
Need Help Pruning a Plum Tree?
If your plum tree appears to be struggling or if you want to increase your chances of a fruitful year, GGM Landscaping is here to help.
We have been handling fruit trees for decades.
We understand how to care for an established tree that has gone several years without attention, when it needs some extra help and deep watering, and when significant main branches need to come out and the wrong cut would leave wounds that take years to close over.
For expert tree maintenance and care or for structural work to help save a neglected tree, our tree surgery team is here for you.
We take the time to assess what needs doing and carry out the work safely at the right time of year.
Call us on 07946 322717 or request a free quote and we’ll take a look.