In order to know if a plant survives and performs in a certain climate, the U.S. Department of Agriculture published in 1965
a first map on plant hardiness zones for North America. Zones were defined based on average annual minimum temperatures
and each of the zones represents an area of winter hardiness for the plants.
Cold temperatures in winter are normally the most important factor if a plant survives or not.
However other factors like humidity, soil etc. are for the plants also of importance in order that they can survive or perform.
But if these would have been taken into account with all its combinations, it would have been too complicated
with too many zones and one would loose the overview.
Below are some links to European as well as to non-European USDA zone maps and some additional information about USDA zone maps.
European USDA Zone map can be found at the following places:
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