Ava, I have kept choc cosmos outdoors in winter...Before I realised I couldn't do that!! Mind you its cornwall! You need to bring it indoors...Now. We all have different ideas about this, as with dahlias, but if it's already in a pot bring it in and wrap fleece around it and keep dry. If its still in the garden knock soil off and wrap in fleece or similar and keep frost off. It's bit harder than keeping dahlias, I think. Maybe in cardboard box, even with dry newspaper. Good luck.