Are they in the ground outside, or in pots indoors? If they are indoors you can cut back anytime. In the garden outdoors, wait until you see the first new growth forming at the base and cut then. Last thing you want in our climate is the hollow stems to get filled with spring rains and then freeze. That'll kill 'em!

GGG

I see these quite often in the Atlanta metro area. They don't get a good head of steam until August. They bloom profusely then linger until about November. At that time, most folks cut them to the ground and toss mulch over the base.

Since we are on the subject over here(I posted on the Brugs forum)...
I received about an 18" rooted cutting from a friends father(with leaves and all) and I am trying to figure out what to do with it. I don't have a south facing window inside to pot it and stick it in, as a matter of fact I don't really have any windows to put it in front of.

Can I keep it inside in rooted stick form until spring? Any other suggestions???