I can't tell from the picture whether its C. alpina or C. macropetala, but it doesn't really matter - both these require no pruning at all, but if you want to restrict its size, you can do it immediately after the flowers have finished.

Thanks v.much - what would you say is the best way to avoid the bottom from beginning to look bare?

Pruning it, but the bottom isn't bare, is it.

It feels much thinner than up top.

Natural growth habit - but you've still got flowers right down to the bottom, so its doing well.

Monty Don said "if it flowers before june dont prune" isnt that a great way to remember it ?

Was it Carol Kline on a recent programe said 'To the ground' all of them?!!!!! I try to keep the label on the plant and keep a note and follow that advice. I should hate to prune your Clem to the ground as it is so pretty. It does need a haircut maybe to stop it rambling too far.