Answer: These plants are not winter hardy in your area, either in the ground or in pots outside no matter what size pot. It can be difficult to overwinter them indoors. Your best shot would be to overwinter them in a cool greenhouse, but you could experiment with keeping them in a garage. Unfortunately, in my experience it is very difficult to overwinter them outside of a naturally warm climate. They are pretty enough that many gardeners are simply happy to replace them each spring just like any other annual.
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