An occasional light frost will likely not kill your established hollyhocks, so long as you are growing them in a suitable zone. That said, if hard freezes are an issue in your climate, your hollyhocks may be safer if you overwinter them indoors. As we mentioned previously, transplanting hollyhocks can be problematic because of their hefty root structures. So, the best solution if you live in such a location is to either 1-keep hollyhocks in a greenhouse or 2-keep them in containers instead of your garden bed. That way, you can just move the containers inside if you have to. Remember, if your hollyhocks spend significant time indoors, you will have to harden them again when you put them back outside.