A damson tree can often remain productive for 50 years. There’s usually no need to prune a damson tree, apart from snipping to keep its shape and cutting back branches if they’re getting in the way.
The best time to prune a straggly damson is early summer, June/July. This will reduce the risk of silver leaf fungi disease (the airborne spores of which are more active during the winter period) and bacterial canker.
Don’t just take it from me!
‘Don’t be tempted to prune stone fruit such as damson in winter as they are prone to the airborne bacteria silver leaf, which is pulled into a winter cut’,
Dan Pearson in The Observer, 28 November 2010.
Monty Don, answering a gardening question in the Daily Mail, says
‘Damsons are by nature small, scruffy trees that do not need nor are improved by pruning. So if you can, just leave it to mature naturally. However, if necessary, the best time to cut it back, as with all plums, is midsummer to avoid excessive bleeding.’