Why do we not prune plum trees in the winter?
There is one specific reason why the Prunus genus of fruit trees, of which plum is a member, are an exception to the winter pruning guidance: silver leaf disease (Chondrostereum purpureum).
Silver leaf is a fungal disease which is infectious between September and May. Spores enter the tree through wounds, so pruning in the depths of winter will leave your plum open to attack.
Signs of silver leaf include a silvery sheen on the leaves followed by branch die-back. Cutting across the branches will often reveal an irregular dark stain, while dead branches will sprout white, woolly bracket-shaped fungi with a purple-brown underside.
By the time April has arrived, your plums will be more resilient to silver leaf and there will be fewer silver leaf spores around.
However, when pruning plum trees, the best time to choose will depend on the age of the tree and its shape.
Pruning plum trees: the best time for young plum trees
Once the winter is out of the way, plums are not as sensitive to pruning as other species of fruit tree. However, when training a young plum, we recommend you prune in April.
For most plum trees, you will be aiming for a bush shape. After removing any suckers (thin shoots) and rubbing out buds near the base of the tree, concentrate on creating an open space in the centre of your tree. This will maximise light and air circulation, boosting fruit yields and reducing the chances of disease. To achieve this shape, target those branches that are growing inwards and downwards for removal, especially where they are rubbing other branches.
If you are aiming for a pyramid shape plum tree, we advise pruning twice a year. While training the tree, reduce the leader (main vertical branch) by two thirds in April and prune back side branches in May. Then, in late June, remove competing leaders before cutting branches back slightly in late July. After the tree has reached its ideal height, you can simply cut back the leader to this level each May while tidying up the side branches.
We have written an in-depth guide to pruning trees, so please refer to that if you are unsure about how to go about pruning.
Pruning plum trees: the best time for mature plum trees
Once your plum trees are nicely established, you can leave pruning until late June or July, when the risk of silver leaf has completely passed.
There is one important caveat to all of the advice above. When pruning plum trees, the best time to remove dead, dying or diseased branches (the ‘Three D’s’), is as soon as possible. These serve only to deprive your tree of energy for fruit production.
Left unchecked, diseases will spread to healthy branches, and dead branches can suddenly fall. While this isn’t a problem with a small plum tree, a branch falling from 15 foot could be a danger to people, pets and property. Since neglected plum trees often produce all their fruit along the upper branches, the extra weight increases the risk of this happening.
Are you having problems pruning your plum tree?
While plum trees are relatively resilient to pruning, like any tree, they will struggle if neglected. If you have mature plum trees which are only producing plums at height, this is a sign that they need serious attention.
27th November 2020
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