Tiffany wrote "I'm not a fan of bumping zone numbers up at all because all it takes is 1 unusually harsh winter to wipe out some/most/all of the marginally hardy plants"
Absolutely! The updated USDA map was barely dry (figuratively speaking), which bumped my zone from 4b to 5, and we had the most brutal winter in many, many years. We have a mountain ash in our back yard that is native up here that was severely stressed by the cold -- well, our frost was down 8 or 9 feet! -- and may or may not bounce back next year. The maps are helpful as a guideline, but there are certainly no absolutes...
