Guide to Pruning Plum Trees

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Quick Facts

  • Suitable for: Plum trees
  • Timing: Early spring (April) or mid-summer (July)
  • Difficulty: Moderate

When to Prune Plum Trees

Plum trees are best pruned in early spring for young trees or mid-summer for established ones. Avoid winter pruning to minimize the risk of silver leaf disease, a common issue for plums and other Prunus species.

How to Prune Plum Trees

There are several methods to prune plum trees, depending on their training form:

1. Bush Form

The bush form is the most common and creates an open-centered tree with a clear stem of about 75 cm (2.5 ft).

  • Size: The ultimate size depends on the rootstock:
    • ‘Pixy’ rootstock: 3 m (10 ft)
    • ‘St. Julien A’ rootstock: 3.6–4.5 m (13–15 ft)
    • ‘Brompton’ or ‘Myrobalan B’ rootstock: 6 m (20 ft)
  • Process: Prune in early spring during formative years to create an open structure. Remove crossing, weak, vertical, or diseased branches. In July, thin crowded branches further if necessary.

2. Pyramid Form

This form produces a smaller tree, ideal for netting against birds.

  • Size:
    • ‘St. Julien A’ rootstock: 2.4 m (8 ft)
    • ‘Pixy’ rootstock: 1.8 m (6 ft)
  • Steps:
    • First Year (July): Shorten new branches to 20 cm (8 in) above a downward or outward-facing bud. Cut side branches back to 15 cm (6 in). Train and tie the central leader to a stake.
    • Subsequent Years (April): Shorten the central leader by two-thirds annually until the desired height is reached, then maintain this height by shortening it slightly each May. Remove competing vertical shoots in late June. Continue to shorten branch leaders and side branches each July.

3. Fan Form

Fan-trained trees are grown against walls or fences using horizontal wires spaced 15 cm (6 in) apart.

  • Size:
    • ‘Pixy’ rootstock: 3 m (10 ft) high by 2 m (6.5 ft) wide
    • ‘St. Julien A’ rootstock: 3.6 m (12 ft) high by 2.4 m (8 ft) wide
  • Process: Trees can be purchased as maidens or partially trained specimens. Prune and train as necessary to maintain the fan shape.

4. Cordon Form

Cordon training is suitable for limited spaces. Consult specific guidelines for this method.

Renovating Neglected or Overgrown Bush Trees

To restore an old, neglected plum tree, stage the renovation over several years:

  • Aim for a balanced tree with an open center to improve light penetration.
  • Large pruning cuts may result in a mass of new shoots. Thin these in summer, leaving just one or two.
  • Use techniques like festooning (tying down young branches to reduce vigour) to control growth. Ties can be removed once branches stay naturally in place.

Common Problems and Solutions

  1. Overloaded Branches:
    • Heavy crops can cause branches to break. Thin fruit to prevent damage.
    • Prune broken branches back to a natural fork to avoid stubs.
  2. Bare Wood Areas:
    • In spring, prune just above bare sections to stimulate dormant buds.
    • For large branches, remove a small section of bark near dormant shoots to encourage growth (notching).
  3. Diseases and Pests:
    • Common issues include silver leaf disease, honey fungus, bacterial canker, pocket plum, plum aphids, and plum moth.

Additional Tips

  • Plum trees are heavy croppers, so thinning fruit and branches is crucial to avoid stress and damage.
  • Regular maintenance pruning and light thinning every summer will ensure healthy growth and fruit production.

For further information on growing and training specific plum tree forms, consult specialized resources or horticultural advice services.

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