Should be done immediately after flowering, removing up to a third off the length of flowered stems, and 2-3 inches off the rest of it if you want. I expect the confusion has arisen because Buddleia davidii requires vastly different treatment - that one you cut back hard at end of March.

Do it after it flowers. and dont be afraid to hard prune it, for eg, have pruned globosa many times, last year hard pruned a fifteen year old globosa, to aprox two feet from the ground, has responded well and will flower its head off this year, over the years it was just pruned a little after each flowering, but it was time to give it a jolly good prune.

Ooh, this is very interesting. I hadn't realised that you had to treat different ones so differently. most of mine are weyeriana....do you know how to prune those?

Karen - same as for Buddleia davidii - March or April, within 2 inches of old wood, cut back hard.

Thank you!