Answer: There are several species and cultivars of Ruellia so whether or not your plant will survive your winter weather depends upon which you have. Ruellia malacosperma is hardy to 10-20F. It is commonly called Mexican Petunia. Ruellia humilis, commonly called wild petunia, is native to Minnesota and will survive your winters. Try to find the cultivar name of your plant - or the common name - or look for some indication on the tag that it is perennial.
As for your question about weather and temperatures, the USDA website is reasonably accurate with its temperature zones. Every garden has microclimates and sometimes you can stretch your zone a little by planting in a place protected by prevailing winds. But for the most part, it is best to choose plants hardy in your zone without additional winter protection.
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