I used to winter them in Western Nebraska where I saw it hit -40 on two different winters and it was -40 every night for more than a month once. The bees did not do well that winter, but if it's only a week or so, they did about as well as they do at -20 F or so. I also sat it hit that in Laramie and the bees survived. I think all my fall honey has always crystallized...