They have grown really leggy, and flopped forwards (onto other plants) a lot. I think that cutting them back will encourage them to grow denser, but how much can I get away with before the plant suffers? Part of the problem is that they are in quite a shady patch - they are flopping forwards to get to the light, maybe, but they have plenty of flowers on so can't be too unhappy.
I've been delaying doing it until the flowers finish - because they look quite pretty - but in that time they have grown even leggier!
Thanks for any advice.