The usual advice from RHS etc is to prune them when the sap is rising so that it seals the cuts against infection from Silverleaf spores landing on them … ie prune from late spring to midsummer.
I never prune any prunus after the end of June.
Gardening in Central Norfolk on improved gritty moraine over chalk ... free-draining.
I agree with dove. Summer pruning won't premote the same boom in growth which is why I would do it over a few years so not to leave it bald. If you cut back a stem it will make it more bushy eventually but like mentioned above, these are trees and you will always be fighting it's instinct to reach for the sky.
Posts
I never prune any prunus after the end of June.
Gardening in Central Norfolk on improved gritty moraine over chalk ... free-draining.