You could also just sink the pot into the ground for the winter. That way the roots would be insulated.
Joann

Yes, they will survive. I'm in northeast Ohio and we have some pretty harsh winters. We have a couple mints planted in 3 gallon pots, they have come back every year for the last 5.

The same with catnip.

I'm with neoguy - I've left spearmint & peppermint outside in pots for more than 20 years and have lost very few. This also works with chives - never had a single pot of chives not come back.

If you want to leave the mint in pots but are afraid it won't survive the winter, before the ground starts to freeze mound mulch or leaves at least 6" around (only 1-2" ontop) the pot(s). Around March/April you can take them out of the mulch to thaw. Once thawed I repot into a bigger pot.

I have a corner of the yard that is dug into a hill that I set all of my potted plants into and then surround them with leaves for the winter, I haven't lost much considering I overwinter about 50+ pots. Also, for pots smaller than 1 gal I dig out the middle of my raised beds and set the pots in the middle and fill in with soil and then let whatever leaves fall on top stay until spring. Needless to say I don't have a greenhouse...yet!

I've had a sweet black peppermint and a Vietnamese spearmint in plastic pots (the kind that look like terra cotta, but lighter) for probably 10 years now, with no problems. The pots are probably 2-3 gallons capacity, and stay on my driveway year-round.

Now that I think about it, I can't remember the last time I divided those, either... really tough to kill a mint...