The United States Department of Agriculture (USDA) assigns Hardiness Zones (HZs) based on the average annual minimum temperature of a region. HZs are numbered from 1 (coldest) to 11 (warmest). Each HZ number indicates a temperature increase of 10 degrees Fahrenheit (F). Temperatures typically increase as elevation decreases (ex. moving down a mountain) or Latitude decreases (ex. moving toward the Earth’s equator). The map above does not show micro-climates within each HZ region where temperatures may be warmer or cooler. You should always contact your local agricultural extension office to find the HZ for your area.

Mighty Trees combines Hardiness Zones 9 & 10.

HZ# Temperature
Range
Color
1 Below -50F N/A
2 -50F to -40F  
3 -40F to -30F  
4 -30F to -20F  
5 -20F to -10F  
6 -10F to 0F  
7 0F to 10F  
8 10F to 20F  
9 20F to 30F  
10 30F to 40F  
11 Above 40F