Although I've had this growing for a few years I've not been able to find out when I should cut this back. I usually take about a third off the top each spring, but the clump is getting taller and taller. So I'm wondering if I'm not cutting enough off. Anyone out there got one as well. I love it for the red berries, that turn black and look fabulous with a frost on them. So it has a good interest all year.
Hypericums on the whole react well to cutting down to ground level, but I have never had this one. They were a weed in our garden when we arrived here some 17 years ago, and we still have the occasional outbreak! I'd certainly cut them back hard now if I were you. I do have a very small one in an alpine bed, grows to about 12 inches, and that gets cut back around now too.
These are a tall variety, currently still with last year's berries on and standing 3ft tall!
This is a cultivar of Hypericum indorum. It doesn't have to be pruned but if it's getting too big you could cut half the stems right back this year and half next. That way you'll still get the flowers and berries and by next year it will be smaller.