The only thing that annoys me more than nay sayers of global climate change (that’s right not global warming), are those ready to embrace some idea of a local warming trend. That is, with the newly restructured zone hardiness map in North America showing formerly zone 3 areas upgraded to 4’s, and so on. These were altered through long term data, based mostly on minimum lows in a hundred year period. Well, guess what? NOAA printed a very long list of US locations that broke historic records for minimum temps. This was the last week of Feb. 2015. These were in Maine, Michigan, Texas, Kentucky, to name a few. These spanned from NY City to Miami.
What does it mean? Perhaps it means we should thing again about thinking anything positive about weather fluctuation. We have always preached caution when planting marginally hardy plants. As of late, we have had a very large number of folks looking to plant peaches and sweet cherries up here in the north, since the hardiness maps lightened up. Only one year later and they have proved invalid. Our state of Vermont just had the coldest February on record, for instance.
Rootstocks choice for trees such as apples are an example of preparing for the unexpected. Our nursery only sells apple trees on cold hardy seedling stock, taking temps down to 40’s below and colder. Compare that with most cloned stocks that are used, almost exclusively, in the US nursery trade. These latter stocks are only designed for zone 5 (15 to -20). This includes all of the Malling stocks. In this situation, a tree on the industry standard, could wind battered and bewildered. That is dead.
You can decide from there.