USDA Zone Definitions

Based on the average annual minimum temperature. Note: Some authors are still using the old USDA Zone designations (pre-1990) so both are listed below.

USDA Zone (1990)	Temperature (Celsius)	Temperature (Farenheit)	USDA Zone (1960)
Zone 1	-45.6 and below	below -50	Zone 1
Zone 2a	-42.8 to -45.5	-45 to -50	Zone 2
Zone 2b	-40.0 to -42.7	-40 to -45
Zone 3a	-37.3 to -39.9	-35 to -40	Zone 3
Zone 3b	-34.5 to -37.2	-30 to -35
Zone 4a	-31.7 to -34.4	-25 to -30	Zone 4
Zone 4b	-28.9 to -31.6	-20 to -25
Zone 5a	-26.2 to -28.8	-15 to -20	Zone 5
Zone 5b	-23.4 to -26.1	-10 to -15
Zone 6a	-20.6 to -23.3	-5 to -10	Zone 6
Zone 6b	-17.8 to -20.5	0 to -5
Zone 7a	-15.0 to -17.7	5 to 0	Zone 7
Zone 7b	-12.3 to -14.9	10 to 5
Zone 8a	-9.5 to -12.2	15 to 10	Zone 8
Zone 8b	-6.7 to -9.4	20 to 15
Zone 9a	-3.9 to -6.6	25 to 20	Zone 9
Zone 9b	-1.2 to -3.8	30 to 25
Zone 10a	1.6 to -1.1	35 to 30	Zone 10
Zone 10b	4.4 to 1.7	40 to 35
Zone 11	4.5 and above	40 and above	Zone 11