Pruning Buxus

I have 4 round  large buxus in containers. When is the best time to shape/prunw them

I have see online July and Septemeber but dont know what is correct.

thanks

Hello, Mike.

The first week in June is the best time to be pruning box (certainly not now). Some  old gardeners would suggest cutting on Derby Day.

I have done them as late as the last week of July but wouldn't leave it later than that as any new growth hasn't time to ripen and harden before the winter frosts and the plants can get badly damaged.