if you are in a situation where you can cover them overnight, i have been able to make a it though a few frosts before harvesting. just make sure you pull the bag off as soon as the sun comes up or you can create a situation favorable to the growth of molds. i have no experience with the frost contacting the buds and subsequently affecting them or their potency, i have always covered up if there was a chance that a frost might come through. hope that helps.