I think you have to carry on watering it till the leaves die off then leave it in a cool dry place until next year, we put ours in the greenhouse when it gets warmer under the potting bench and it comes out the next year.
If anyone knows different please put me right :o)) Jackie x

Jen check out Balcony's blogs, he grows some real beauties and has written some very good imformative blogs over his years on goy...

check on spritzhenry's blogs she did a very comprehensive one a few years ago now.

I do keep them yr on yr and they flower in april/may for me.