Plum trees do not require as precise pruning as apples and pears, but still benefit from initial training and the thinning of old wood to ensure they produce as much fruit as possible. Plums are pruned in early spring or mid-summer to avoid infection by silver leaf disease.
Timing: Early spring or mid-summer (April or July)
When to prune plums
Avoid pruning plums in winter, as it increases the risk of infection by silver leaf disease to which plums and other Prunus species are prone. The best time for pruning is usually spring for young trees and mid-summer for established ones.
How to prune plums
There are three commonly used methods of pruning plums: bush, pyramid and fan. Plums trained as cordons are gaining popularity too.
The bush is perhaps the most popular method of training and pruning and creates an open-centred tree with a clear stem of 75cm (2½ft). Its ultimate size will depend on the rootstock it is grown on. Trees grafted onto ‘Pixy’ rootstocks will reach 3m (10ft), ‘St. Julien A’ 3.6-4.5m (13-15ft) and the ‘Brompton’ and ‘Myrobalan B’ 6m (20ft).
The overall aim of pruning is to create an open-centred tree. This begins with the same formative pruning as apples and pears but, importantly, is carried out in early spring.
On established trees, rub out any buds developing on the lower trunk and carefully pull off suckers arising from the rootstock. Pruning is mostly limited to removing crossing, weak, vertical and diseased material. If the plum tree is still crowded, then further thinning can be done in July.
A pyramid plum tree is considerably smaller than a pruned a bush, and this makes it practical to net against birds. Plums on ‘St. Julien A’ rootstocks are kept to 2.4m (8ft) and on ‘Pixy’ rootstocks to 1.8m (6ft).
After the initial pruning, follow these steps:
During the first summer:
- Prune in the third week of July when the young shoots have finished growing. Shorten new branches to 20cm (8in), cutting above a downward or outward-pointing bud
- Cut side branches back to a bud at 15cm (6in)
- Train and tie in the central leader to the stake
In subsequent years:
- During April, shorten the central leader by two-thirds.
- Repeat annually until the tree has reached 2.4m (8ft) on a ‘St. Julien A’ rootstock, or 1.8m (6ft) for ‘Pixy’, after which, shorten the central leader to 2.5cm (1in) or less each May, to keep the tree at the same height
- Vertical shoots at the top that compete with the central leader should be removed in late June
- In the third week of July, shorten branch leaders to 20cm (8in), pruning to a downward or outward-facing bud in the axil of the leaf. Cut side branches back to a bud at 15cm (6in)
A fan-shaped tree is created by training against a wall or fence with horizontal wires fixed 15cm (6in) (or two brick courses) apart. Trees can be bought as maidens, or partly trained. Expect the height and spread of trees on ‘Pixy’ rootstock to be 3m (10ft) high by 2m (6½ft) spread and trees on ‘St. Julian A’ to be 3.6m (12ft) by 2.4m (8ft).
Where space is particularly limited, plums can be trained as cordons. See our plum cordon page on this technique for more details.
Neglected and overgrown bush trees
Renovating an old, neglected plum tree should be staged over several years. Aim for a well-balanced tree, keeping the centre of the crown free from shoots to allow good light penetration. Trees respond to larger pruning cuts by sending up a mass of new shoots. Where this happens, the shoots will need to be thinned in the summer to leave just one or two.
The tying down of young, flexible branches to the horizontal can reduce excess vigour in large, unruly trees. This technique is known as festooning, and is best done in the summer. It can help prevent trees becoming overgrown, and is also effective for pyramid plums.
Ties are left in place until the branch stays naturally at the new position, usually the following spring. Attach one end of the tie to the branch tip, and the other end to a stake or the trunk.
Plums can be heavy croppers, leading to branches breaking under the weight of fruit, so thinning is important to prevent damage. Branches already broken should be pruned back into undamaged wood, ideally cutting back to a natural fork to avoid leaving stubs.
Bare wood areas can be difficult to remedy on fruit trees. Here are a few techniques to try:
- In spring, stimulate dormant buds by pruning back to just above the bare section.
- For large branches, before new growth starts in spring, remove a small section of bark from just above a dormant shoot where you want to encourage growth. This technique is known as notching, and aims to restrict the flow of suppressive growth hormones from further up the shoot to stimulate growth in the treated bud.
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