Quick answer

Prune an established plum in July or the first half of August, small cuts only after that, and a young one in early spring as the buds open, inside the spore season but on cuts small enough to close fast. Nothing in autumn or winter, bar a branch you have confirmed as silver leaf: spores run from September to May and cold wounds close slowly. Bacterial canker is not an exception; that cut waits for July or August. Rain forecast? Wait for a dry spell. Leaves turning? Wait for next summer, or next spring on a young tree.

Ask when to prune plum trees in the UK and the awkward part is that the tree looks most prunable at exactly the wrong moment. A bare plum in February is easy to read and wide open to silver leaf.

The safe windows are summer for a cropping tree and spring for a young one. Which is yours depends on the tree's age, its training and whether it is already diseased.

Table of contents

What to look at before you decide

Five checks, most of them a ninety-second look, nothing to buy. They settle more than the date does: a plum in Truro and one outside Aberdeen are not on the same schedule.

How old the tree is

Newly planted, first year in the ground. Almost nothing comes off. Frank P Matthews says new trees, bare root included, need very little pruning in their first year, and the RHS sets the timing at April, not winter. Missed April? Leave it alone this year and make the first formative cut next spring, as the buds open.

Young and still being shaped, growing seasons two and three. The one stage where spring, not summer, is the mainstream answer. Gardeners' World prunes young trees lightly as the buds burst; the RHS says early spring, after they open. Pick three or four well spaced main branches and cut to outward-facing buds.

Spring sits inside the spore season, which is why it is the exception and not the rule: a young tree's cuts are few and small, on wood that is about to grow away and close them. Keep the spring work light: the framework cut above, plus anything dead, broken or crossing.

Established, from its fourth season on, whether or not it has cropped yet. Summer, and the work shrinks to crossing, weak, vertical and diseased wood. A Victoria, one of the best known eating plums, joins this group in its fourth summer.

On the line? Go by the tree, not the birthday: still filling out its framework, young; cropped last year on a settled framework, established.

Free-standing, or trained flat against a wall

A bush or half-standard in the open is pruned once a season. A pyramid runs longer, and takes its July cut whatever the tree's age: the RHS shortens its central leader in April, then comes back in the third week of July for the branch leaders. A fan runs a different rhythm again, and runs it from its first summer whatever the tree's age: shoots pinched back through June, shortened again in late July or early August, wall-pointing shoots rubbed out with a thumb while soft. A fan is the usual way to train a plum flat against a wall, because the RHS says stone fruit is not suited to training as an espalier.

The trained form buys an escape route. RHS guidance on established fans lets the replacement pruning of late cultivars, still hanging in autumn, wait until spring. Replacement pruning is taking out one or two of the oldest fruited branches each year and tying in a young shoot to replace them, keeping young wood in the framework.

Whether this year's shoots have stopped growing

This is the signal that beats the calendar. A shoot tip still soft, pale and floppy is extending; once it has set a small tight bud and the top few centimetres have gone firm, growth is over. The shoot is the test, not the date.

On a fan the June pinch removes the tip the test reads, so that one runs on the date: once the pinched shoots have gone woody at the base, the second shortening is due.

Whether any leaves are silvered, and what is inside the wood

Silver leaf is the fungus Chondrostereum purpureum, and it shows as a silvery sheen over one branch or one side of the tree, clearest on plums. Do not cut on the leaves alone: silvering with no staining inside the wood is false silver leaf, brought on by cold, drought or another non-disease stress, and that branch is not infected. Not infected is not the same as healthy, though: Suffolk Fruit and Trees puts false silvering down to drought or malnutrition.

The confirming test is a cut across the branch, and it wants wood of some size: Suffolk Fruit and Trees puts the brown staining on wood 2.5cm across or more, and says it shows more clearly if you wet the cut face. Thinner than that and the cut face will not read either way, so a slim silvered shoot stays unconfirmed and the silvering itself is all you have to judge on. An irregular dark stain in the centre, not following the heartwood, means the real thing, and the RHS cuts 10-15cm (4-6in) beyond where the staining stops. Get the wood off site: fruiting bodies form on it as it lies.

Confirmed silver leaf is the one thing that overrides the calendar entirely: it comes out in whatever month you find it. The RHS cuts affected branches as soon as possible, certainly before the fruiting bodies appear, and NIAB is the reason for the hurry: a living silvered branch is not yet a source of infection, but once it dies the fruiting bodies follow and the spores with them. So: dry day, 10-15cm past the staining, burnt or binned the same day.

Whether there is sunken dead bark, or shotholes in the leaves

Gum on the bark by itself means very little. The RHS notes that gum production from the bark of Prunus is quite common and, without dead sunken bark, likely to have come from something other than bacterial canker: physical damage, or environmental stress.

What you are looking for is sunken dead patches of bark in spring and early summer, often oozing gum, and round brown leaf spots that drop out as though the leaf had been shot. That is bacterial canker, a Pseudomonas syringae infection. No fungicide spray is available to amateur gardeners, so cutting it out is the only treatment, and the RHS still times that cut for July or August, back to healthy tissue. It calls the disease serious and able to kill larger branches or whole trees, so mark the wood now rather than let the summer window pass.

Paint that wound promptly. Elsewhere on a plum, wound paint is only worth it where silver leaf keeps recurring.

Month by month, August round to July

Sources disagree about the edges. On established trees the RHS bacterial canker page is tightest: where possible, all pruning in July or August, when tissues are most resistant. Gardeners' World opens from mid-June, Frank P Matthews stretches to early autumn, Ashridge Nurseries prefers bud break to midsummer.

They do not agree at the far end either. Frank P Matthews is content pruning into early autumn, and Ashridge calls the winter risk small and mainly a commercial grower's problem. What the four share is the growing season, and the only month inside all their windows, on the usual reading of Ashridge's mid-summer, is July. NIAB sits further in still, putting the job in late spring to early summer, though it agrees with the four that autumn and winter are out. Read mid-June to late August as the outer limit and July as the target: the cost of pruning in July is a few developing fruits, which Gardeners' World tells you not to worry about, and the cost of being wrong about February is a dead branch.

Damsons and gages take the same window: Suffolk Fruit and Trees gives the September to May prohibition for plums, greengages and damsons together.

August, and the closing of the window

Late August is the tail of the season, not the middle. On an established tree a crossing branch or a few thin shoots can still come off in a dry spell. A reshape cannot: a wide wound opened now goes into September still open. A free-standing bush or half-standard in its first three seasons is not in this paragraph; its window was spring.

September and October, when the tree looks ready and is not

Put the secateurs down, with one exception: a branch confirmed as silver leaf, or one already carrying brackets, comes out now rather than in July. Otherwise silver leaf spores turn active from September, and the RHS names mid to late autumn alongside the dormant season as the time to avoid. Pick the fruit and rake up what falls.

November to January, the do-nothing months

No routine pruning. Wounds close slowly in cold wet wood, and NIAB puts spore production at its greatest now. Ashridge is the outlier, calling the winter risk small and largely a commercial grower's concern; the RHS, Gardeners' World and NIAB say keep off. Firm stakes, check ties are not cutting in, and look over any dead wood for brackets with a woolly white top and purple-brown underside.

Find one and that branch is already producing spores: take it out and get it off site rather than waiting for July. Ashridge Nurseries removes dead, damaged and diseased wood at any time of year, and this is the case for it.

February and March, the months people get wrong

A bare plum in February is easy to see into and completely off limits. Every apple and pear nearby is being pruned, which is where the mistake starts. Walk round with soft string, loop it on each branch you mean to remove, then leave the tree until summer. Bare-root planting season too, and a plum that goes in now waits until April.

Young trees are the exception, and in a mild spring or a southern garden their buds can be moving by March. Once open, the formative cut can start. Everything else waits.

April to June, young trees then the summer window

Once the buds open, young trees get their formative cut. Cropping trees are left alone, with two exceptions: a trained fan carrying a late cultivar, which takes its replacement pruning now, and wall-pointing shoots on any fan, rubbed out with a thumb while soft.

From mid-June the window opens on established trees. Thin the fruitlets first: the RHS reduces them to one every 5-8cm (2-3in) or a pair every 15cm (6in), which is the difference between decent plums and a snapped branch.

July, the best month of the year for it

If you do this once a year, do it now. Growth has stopped extending, tissues are at their most resistant, spores are fewest and there is season left for the wound to close. Northern gardens run two to three weeks behind the south, so read the shoots, not the calendar. On an established tree, that is; a young one had its turn in spring.

Making the cut, step by step

This is the summer prune on an established tree. A young tree's formative cut is a lighter version of Steps 1, 2, 3 and 4, plus the framework cut described above, done in spring as the buds open: ignore Step 1's July date, but not its dry spell.

Step 1. Wait for a dry spell, and check the tree is ready

Stone fruit is pruned only in dry weather, and the RHS is unambiguous about it, so wait for a settled few days rather than a dry morning. Then check the shoots: the RHS cuts in the third week of July, once the young shoots have finished growing.

Step 2. Clean the blades, and clean them again between trees

Blades go from branch to branch, so wipe them with a garden disinfectant before the first cut, between trees and after anything you suspect. NIAB tells plum growers to disinfect between cuts, and our notes on cleaning garden tools cover what shifts dried sap.

Step 3. Take out the dead, the broken and the crossing first

On an established tree this is nearly the whole job: dead wood, anything the wind has torn, and branches rubbing across each other, cut to a healthy junction rather than a stub.

Live plum wood wants a slicing cut, which is what a sharp pair of bypass secateurs gives you. An anvil blade presses onto a flat plate instead: fine on dead wood, but on live wood it crushes, and the ragged wound is the entry point. If gripping a standard pair is the problem, a ratchet pair with bypass blades does the same job with less hand force. Check the blade before you buy, because the ratchet is only a force mechanism and Draper notes ratchet secateurs come with either bypass or anvil blades.

Step 4. Open the middle and lose the verticals

The RHS limits the established bush prune to crossing, weak, vertical and diseased material, and Gardeners' World describes the target as an open wine glass, or goblet. Shoots growing into the centre shade the wood that would carry the fruit.

Step 5. Shorten this year's growth, but only on a form that needs it

Skip this step on an open bush or a half-standard: Step 4 was the job there. Gardeners' World is looser on an established bush, branches back by about a third and side shoots by half, but that goes past the RHS limit in Step 4, and taking a third off every branch will usually blow past the whole-tree third in Step 6. Taking too much at once is what produces a forest of water shoots.

Annual shortening belongs to the restricted forms, which are built on it. On a free-standing pyramid the RHS shortens new branches to 20cm (8in) above a downward or outward-pointing bud, and side branches to a bud at 15cm (6in).

Fans are measured in leaves rather than centimetres: pinch a shoot with seven or eight main leaves back to six, then shorten it to three in late July or early August.

Step 6. Stop at a third of the whole tree

Frank P Matthews caps it at about a third of the tree in any one year, which is a different measurement from shortening a branch by a third: judge it by the pile on the ground. Beyond that, the RHS stages renovation across several years. The cap covers routine work; confirmed diseased wood comes out however much there is.

Step 7. Pull the suckers, then clear the prunings away

The RHS rubs out buds developing on the lower trunk and pulls rootstock suckers off rather than cutting them. Get the prunings off site the same day: silver leaf fruits on a heap of brash just as readily as on the tree.

What goes wrong, and how to recover

You pruned in winter and the leaves came back silvery. Do the staining test first, because a stressed tree silvers too. If it is confirmed, take the branch out and get it off site rather than stacking it. The RHS does not promise an infected tree recovers, so treat this as containment.

The tree threw up a forest of upright shoots. That is the usual answer to taking too much off at once. Rub them out with a thumb the following summer while they are soft, and resist meeting a thicket with another hard cut.

A branch split under the weight of fruit. Most plums set more fruit than their wood can hold, and Ashridge Nurseries singles out Victorias as famous for breaking under the weight of their crops if they are not thinned. Tidy the tear back to healthy wood in the summer window rather than leaving a ragged stump, then prevent the repeat by thinning fruitlets and propping laden branches.

Frequently asked questions

Is it too late to prune a plum tree at the end of August?

At the end of August, small cuts on an established plum are still fine in dry weather; a reshape is not. The RHS bacterial canker page puts all pruning, where possible, in July or August, and spores turn active from September. A fan's second shortening belongs to late July or early August, and the RHS wants stone fruit on a fan finished by late August, so a dry day this week is the last of it. A free-standing bush or half-standard in its first three seasons is not in this window: young trees get their framework cut in spring. A young fan is the exception, because the RHS manages a fan's re-growth through the summer from its first season. Anything needing a saw waits for next July.

Can I prune a plum tree in February?

No, and a bare February plum is the most tempting mistake in fruit growing. The RHS avoids pruning plums in the dormant season and in mid to late autumn, because wounds close slowly in the cold and infectious spores are about from September to May. The one thing that does come out in February is a branch you have confirmed as silver leaf, or dead wood already carrying its brackets. Bacterial canker is not in that exception: the RHS times that cut for July or August, so mark the wood now and cut it then.

My plum has silvery leaves. Should I cut the branch off straight away?

Cut into the branch before you cut it off, because silvering alone does not confirm silver leaf. Silvering with no dark stain inside the wood is false silver leaf, brought on by cold, drought or another non-disease stress, and that branch is not infected. The staining shows on wood 2.5cm across or more, so wet the cut face and look for a dark irregular stain in the centre; on thinner wood the cut face will not read either way, so that branch stays unconfirmed. A confirmed branch comes out in whatever month you found it.

When do I prune a plum that does not ripen until October?

In the same summer window as any other plum, with the fruit still on the tree. Waiting for the harvest on a late cultivar such as Marjorie's Seedling pushes the job into October. On a trained fan, the RHS lets replacement pruning of late cultivars wait until spring instead.

When do I prune a Victoria plum tree?

A Victoria takes the standard rule: a light spring cut for its first three seasons, then July or the first half of August once established. Thinning matters more on this one than the pruning does, because Ashridge Nurseries says Victorias are famous for breaking under the weight of their crops if they are not thinned. The RHS reduces the fruitlets in early summer to one every 5-8cm (2-3in) or a pair every 15cm (6in).

Do I need to paint or seal a plum pruning cut?

Not as a routine. The RHS treats wound paint as worthwhile only where silver leaf is a recurring problem, so on most plums a clean cut with sharp blades in a July dry spell is the whole of the protection. Bacterial canker is the exception: there the RHS cuts back to healthy wood and paints promptly, to keep re-infection out.