Um, you might want to rephrase your question - at the moment, you appear to be asking what you should do with pots during the winter - wash them and store them if they're not frost proof, is the answer. But I'm not sure that's what you really want to know, is it?

Maybe it's to do with Campanulas in a pot? If it's that, then my answer would be to plant it out, as they're (mostly) hardy perennials, apart from the odd biennial. I'm only guessing, though..

If Guest is asking about overwintering a campanula in a pot, then I would do nothing special. They are a hardy plant and can withstand the pot freezing. Whether or not the pot is frostproof is another matter and I could not judge that without seeing the pot.