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.
How to prune plums
There are three commonly used methods of pruning plums: bush, pyramid and fan.
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, 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).
The pruning of a newly planted tree is the same as for apples and pears. Remember: carried out in April not winter to avoid silver leaf disease.
Afterwards 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. Also 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 competing with the central leader should be removed in late June
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).
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 and can help prevent trees becoming overgrown.
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.