Cut off as much as you like, then a bit more, these thrive on being cut down. Don’t worry about it being just bare trunks, it will soon grown, then try to keep it in check each year.
Gardening on the wild, windy west side of Dartmoor.
Ditto Lyn. that's just what I do. They are great. The only problem is as a hedge, I trim with a hedge cutter, then over time wander along with my secateurs cutting the jagged bits off.
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I live in west central Scotland - not where that photo is...