Plums are a joy. Who can pass an enticing bowl without sampling one of these ripe, succulent fruits? But, as ever, the trees need tlc, pruning and disease control, if they’re to provide such a tasty harvest next year.
Correct pruning ensures a healthy productive tree. Although a plant must heal the wounds we make by pruning, many species, like apples, can carry out these repairs at any time of year.
But all members of the prunus genus, plums, greengages, cherries, peaches, nectarines, apricots, and ornamental prunus, are not so easy-going. The fungal disease, silver leaf, can attack open wounds and soon kill the trees. So, pruning must be done when wounds are quickly healed.
This happens between spring and autumn when the sap is up and a plum is actively growing. So there’s still just time to prune this genus of trees.
Silver leaf can also enter open wounds caused by broken branches or damage to the bark of a tree incorrectly attached to a stake.
The fungus releases toxins which spread through the tree, cause tell-tale dark brown stains in the wood and penetrate the leaves. These toxins disrupt leaf tissues and allow air to enter the leaves, making them look silvery. The fungus itself doesn’t damage the tree: the now useless leaves stop photosynthesising.
There are 2 feasible times to prune: once buds have burst in spring, or after harvest, provided the tree is still growing and leaves haven’t started discolouring. You can prune early and mid-season varieties now, but will need to wait till next year with later fruiters, like Marjorie’s Seedling.
Rather than training plum trees, I grow them as bushes partly because they crop better. Like other top fruit, plum varieties are grafted on rootstocks which control their vigour. Most readily available trees are grafted on to St Julian A, which produces a 3.5 -4m tree. A few are grafted on ‘dwarfing’ Pixy which reaches 3m.
You can’t fight the rootstock to get a significantly smaller tree, but should always remove skyward growing stems. A young tree’s leader should be reduced to around 1m high, just above the junction with several side branches. This encourages 4 or 5 of these branches to grow strongly, leaving the centre open and airy. I find this makes harvesting from the ground much easier or I nip up the gently sloping boughs of a mature tree for the higher fruits.
Otherwise, keep pruning to a minimum, encouraging fanning branches and removing crossing ones. And remove any sucker growth the moment you see it.
If you’re still harvesting, look out for Brown Rot. This disease is caused by various strains of the Monolinia fungi and is very common during the wet weather we’ve been having. Plums turn soft and brown before developing cottony pustules and the fungus spreads rapidly though fruit clusters. They may spread into fruiting spurs and twigs where they may cause caner.
The fungus overwinters in cankers and mummified fruit. It can also cause spur wilt where flowers and then leaves of a twig wilt and turn brown. Cut and destroy immediately. That’s easier said than done on a big tree, but get what you can. And be sure to rake up and landfill any damaged fruits.
Trees are more susceptible in poorly drained soil, or if overfed with high nitrogen fertilisers, causing a potassium-nitrogen imbalance.
And, like me, you’re probably cursing all these split plums just now. Sadly, it’s the inevitable result of our recent wet weather following on the heels of a long dry spell. Keep picking them off early to prevent rot spreading, cut out any bad bits and stew.
Plant of the week
Aster amellus is a European autumn daisy that provides blue, purple and pink shades from late summer to October. ‘Veilchenkonigin’ has thin ray florets in an intense lavender purple.
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