Pruning plum trees is an essential practice to ensure they grow healthily and produce as much fruit as possible. While plums do not require the precise pruning needed for apples and pears, proper care in their training and thinning is still crucial. Here’s a breakdown of when and how to prune plums effectively.
When to Prune Plums
- Avoid winter pruning: Pruning in winter increases the risk of infection by silver leaf disease, which plums are especially prone to.
- Best timing:
- Early spring: Ideal for young trees.
- Mid-summer (July): Best for established trees.
How to Prune Plums
There are several methods for pruning plums, each suited to different tree shapes and growth habits.
- Bush Training
- Goal: Create an open-centred tree with a clear stem (75 cm or 2.5 ft).
- Rootstock impact: Depending on the rootstock, the tree’s size will vary:
- ‘Pixy’ rootstock: 3 m (10 ft)
- ‘St. Julien A’: 3.6-4.5 m (13-15 ft)
- ‘Brompton’ and ‘Myrobalan B’: 6 m (20 ft)
- Pruning Steps:
- In early spring, start by forming the tree with the same formative pruning as apples and pears.
- On established trees, remove buds on the lower trunk and suckers from the rootstock.
- Regular pruning involves thinning out crossing, weak, or diseased growth.
- July Thinning: If the tree is crowded, perform additional thinning to improve air circulation and light penetration.
- Pyramid Training
- Smaller size: Suitable for trees on ‘St. Julien A’ (2.4 m or 8 ft) or ‘Pixy’ rootstocks (1.8 m or 6 ft), which makes them easy to net against birds.
- Initial Pruning (spring): Prune as you would for apples and pears.
- After First Summer:
- Prune in July when the young shoots have finished growing.
- Shorten new branches to 20 cm (8 in) above a downward or outward-pointing bud.
- Cut side branches back to a bud at 15 cm (6 in).
- Train and tie in the central leader to the stake.
- Subsequent Years:
- In April, shorten the central leader by two-thirds.
- Keep shortening the central leader each year to maintain the desired height.
- In late June, remove vertical shoots that compete with the central leader.
- In July, repeat the pruning of branch leaders to 20 cm (8 in).
- Fan Training
- Trellising: Plums trained in a fan shape are typically grown against a wall or fence.
- Spacing: Wires are fixed 15 cm (6 in) apart to train the tree.
- Tree Size:
- On ‘Pixy’ rootstock: 3 m (10 ft) height and 2 m (6.5 ft) spread.
- On ‘St. Julien A’: 3.6 m (12 ft) height and 2.4 m (8 ft) spread.
- Cordon Training
- For limited spaces, plums can be trained as cordons, a vertical form ideal for smaller gardens.
Dealing with Neglected and Overgrown Bush Trees
Renovating an old, neglected plum tree requires patience:
- Stage Renovation: Gradually prune over several years to balance the tree’s growth.
- Thinning: Focus on removing excess shoots from the tree’s centre to improve light penetration.
- Handling New Shoots: If large pruning cuts lead to excessive new growth, thin the shoots during the summer to keep the tree well-formed.
Controlling Vigour
Excessive vigour can cause trees to grow too large. A technique called festooning helps manage this by tying down young, flexible branches to the horizontal. This technique reduces unnecessary upward growth:
- Tie Down: Attach one end of the tie to the branch tip, and the other end to a stake or the tree trunk. Leave ties in place until the branch naturally stays in position, which typically happens by the following spring.
Common Problems and Solutions
- Overcropping: Heavy crops can break branches. To prevent this:
- Thin the fruit early in the season to reduce weight.
- Prune broken branches back to undamaged wood, cutting to a natural fork.
- Bare Wood: Address bare wood areas by:
- Spring Notching: Prune just above dormant buds to stimulate growth in bare sections.
- Removing Bark: For larger branches, remove a small section of bark above dormant shoots to encourage new growth.
- Diseases: Watch out for silver leaf disease, honey fungus, bacterial canker, plum aphids, and plum moths. Prompt pruning and correct care can help mitigate these threats.
By following these methods, you can ensure your plum tree thrives and produces abundant, healthy fruit. Regular pruning in the right seasons and using the appropriate techniques based on your tree’s growth form will help you maximize your tree’s productivity and longevity.