There's some advice here: http://www.kirmandesign.com/pruninggroup01.asp and here: http://www.gardenersworld.com/forum/thread/?threadId=81266. I had to prune mine quite hard in 2014 as it had gone mad and left what I thought was only dead woody stems, but last year there was new growth out of these and the flowers this year have been fantastic. So be prepared to go without flowers for a year if you prune it back hard.
Replied: Thursday 26th of May 2016 04:18 PM
