One additional thing that is important to note is the duration that the
plant is exposed to extreme temperatures. A sustained exposure to -40F
temps for a day would probably do more damage than an hour at -45F temps.
At the University of Saskatchewan last year they had -49F for 1 hour, and
some of their cherries escaped with no damage. Lon has also mentioned that
there are some Montana vitis riparia grapes that have survived -70F temps.
I have to be honest, after supercooling fails at -40F I don't know what
process allows plants to survive these extremes.
Dean Kreutzer
Regina, Saskatchewan Canada
USDA zone 3
[NAFEX] Hardiness Additional info,
Dean Kreutzer, 10/19/2004