Cut it back and let it dry out. Remove it from the pot and keep it frost and mouse free over the winter. If you prefer you can keep it in the pot as long as it is dry - otherwise its a good idea to cover it with dry sand, sawdust, compost etc.

I have kept mine for several years now. The first year I tipped the pots on the side in the back of the open shed until they dried out, tipped them out and wiped off most of the earth and stored them in sawdust in polystyrene boxes (the sort greengrocers have broccoli come in) they kept well, if you can stop the mice eating the polystryrene! Last year I was lazy and just tipped the posts on the side and left them in the back of the barn with some paper sacks over the top, but may have lost one or two to mice - mind you the weather was mild last year, so might not always get away with that!