Hardiness Zones

Hardiness Zones are geographic areas delineated based on their average minimum temperature. They allow to know which plants may withstand winters in a region. This analysis assumes that plants can not tolerate prolonged low temperatures, including prolonged frosts. The plants die and their chance to leave the roots are uncertain. The winter of 1985 was very rigorous in Europe and several eucalyptus and mimosas, even in southern areas, were frozen. The mimosas survived but not eucalypts.
It is up to 12 different areas in different countries. Each zone is itself divided into sub-areas of suffixes "a", "b" and "c" (area "c" is slightly warmer than the others).
For example, a plant hardiness 4b can be grown without special protection in areas greater than or equal to 4b. By cons, it may not withstand the harsh winters of a lower zone (from 0 to 4a). In winter, protective measures would be required.
Cold hardiness is not the only criterion to be observed: the hardy trees do not necessarily heat. Thus, the trees of the northern regions, such as birch or walnut, do not support high temperatures.

Zones in Europe