Plum tree pruning is a task you only need to do once a year to ensure healthy growth and reduce the chance of any problems from developing. Different types of plum tree require slightly different pruning processes, although most are relatively straight-forward to do, while the age of the tree also influences the type of pruning required.
Pruning your plum tree once a year is always worthwhile. It allows you to properly manage the shape of the tree and stop it from getting out of control, while also maximising the amount of fruit to expect.
Never Prune Plum Trees During Winter
Before getting into the best time to prune a plum tree here in the UK, it’s important to know when not to prune one. Never prune your plum tree during the winter! While growth is dormant, the tree becomes more susceptible to silver leaf disease.
Silver leaf disease is a fungal infection common to plum trees that produces spores during the winter, which is why you want to avoid pruning during this period. If you have pruned the plum tree during winter with your pruning saw and notice silver leaf (a silver sheen develops on leaves or whitish-purple fungus on branches) then you need to immediately remove the effected branches.
When to Prune
The best time to prune a plum tree in the UK is either spring or mid-summer. If your plum tree is still young and developing, look to prune during spring rather than summer, which is best saved for more established plum trees.
How to Prune a Plum Tree
There are several methods used to prune plum trees with bush, pyramid, fan, and cordon being the most widely used methods. The type of rootstock will also impact each of these pruning methods, namely how large the tree grows.
Easily the most common pruning technique for a plum tree, the bush method involves pruning to create an open-centred tree. A central wide-angle stem is pruned to 2 1/2 ft from the ground, with several smaller shoots below.
The final height of a bush prune plum tree is determined by the type of rootstock, with Pixy rootstocks reaching around 10ft, St Julien A rootstocks reaching between 13-15ft, and Myrobalan 3B approximately 20ft.
Bush pruning focuses on creating an open-centre tree in younger trees, although the process is still used in more established tree too. Simply prune away any buds that develop on lower portion of the tree trunk, removing any suckers that rise from the base of the rootstock.
To create the open-centre, you want to prune away branches with some pruners or garden shears at the top of the tree that are crossing or vertical, while also removing any weak or diseased branches that have developed over the year. Should the open-centre still look overcrowded after spring pruning, prune again during the mid-summer (around July).
Related: How to prune a bay tree
A different pruning process is used for pyramid plum trees as they are generally much smaller compared to bush plum trees, reaching around 6ft (Pixy rootstocks) or 8ft (St Julien A rootstocks).
The process is the same as creating a bush prune tree when the tree is new, pruning above a wide-angle central stem to encourage balanced branch growth from an open centre. After doing this in spring the tree is then pruned with tree loppers again in summer.
This involves pruning the newly established shoots around the 3rd week in July, making them around 8-inches long. After this, cut away side branches until they are a bud – around 6-inches long. Once this pruning is done, you tie the central stalk to the stake.
Wait until the next spring and remove the height of central stalk by around two thirds. Repeat this process again each subsequent spring until the tree is 6ft (Pixy rootstock) or 8ft (St Julien A rootstock).
After reaching these heights, simply prune away additional height from the central stalk to maintain the 6ft/8ft height. If any vertical shoots reach a similar height as the central stalk, prune these away during late June.
Also, prune any branch leaders to about 8-inches and any side branches to 6-inches in late July, repeating annually with above pruning.
Fan training is a process that involves creating a fan-shaped tree by fixing it to fences or walls using horizontal wire. It’s a method you can use on partly trained or maiden trees and will produce trees that are around 10 ft x 6ft (Pixy rootstock) and 12ft x 8ft (St Julien A rootstock).