Hardiness Zones

To obtain the Hardiness Zone of a region it is necessary to record the absolute minimal yearly temperature over several years. The number of the Zone is given by the average of those temperatures according to the following table (Celsius/Fahrenheit converter):

Fahrenheit Zone Celsius
Below -50 1 Below -45.6
-50to-40 2 -45.6to-40.0
-40to-30 3 -40.0to-34.4
-30to-20 4 -34.4to-28.9
-20to-10 5 -28.9to-23.3
-10to0 6 -23.3to-17.8
0to10 7 -17.8to-12.2
10to20 8 -12.2to-6.7
20to30 9 -6.7to-1.1
30to40 10 -1.1to4.4
Above 40 11 Above 4.4

The temperature is one limiting factor among several others such as humidity, soil conditions, insolation, exposure to wind.
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