I really don't know how to answer that, Tom, as the zones seem to not always hold true for frosts and freezes. We usually don't have our first frost until after Thanksgiving, but it came early this year and we are forecast to have a mild winter. The freeze that came last night was a hard one and most everything that will get hurt by it, DID !!! The majority of my brugs are inground and my brug cutting event is as near the middle of November as possible. This year's temps were in the mid seventies with a nice breeze blowing, so we were all very comfortable "doing the deed of cutting them back" !! I had not cut my very large Dr. Seuss, so just threw a frost protector over him, and his cuttings are still viable. He has seven trunks this year, so most everyone who wants a trunk cutting will get one. I will cut him back tomorrow.
USDA Zone 7/8
North Central Texas