Heat Zones

To obtain the Heat Zone of a region it is necessary to record the number of days per year during which the temperature will go above 30° C [86° F]. The Zone-Index is given by the average of those days according to the following table:

Average number
of days per year
above 30° C [86° F]
Below -1 1
1to7 2
> 7to14 3
> 14to30 4
> 30to45 5
> 45to60 6
> 60to90 7
> 90to120 8
> 120to150 9
> 150to180 10
> 180to210 11
Above 210 12

This Heat Zone Index was designed by the American Horticultural Society (AHS). The average is calculated over a period of 12 years (7 years in some cases, when data are missing).
The temperature is one limiting factor among several others such as humidity, soil conditions, insolation, exposure to wind.
Back         Home