Dear Susan, I do not use zones as they do not work! For instance they say the Shetland islands are zone 8, no trees can grow there as it is cold and the the wind is evil. The next stop from the Shetlands is the north pole.
Yet is rate it the same as some place in America that has 70F more in the summer than than the Shetlands, just because the winter temperature is the same. However in he Shetlands it snows and never stps, whereas in this place in America it does not!
If snow covers a plant it insulates it, unless you get permafrost.
Even the American Horticultural Society have stated that zone maps do not work. They have put us down to zone 8 because of three bad winters, which is the same as the Shetlands, and I grow palms in my garden.
Regards.
Neil.
