North American hardiness zones

Zone 1: below -46°C (below -50°F) 
Zone 2: -46 to -40°C (-50 to -40°F) 
Zone 3: -40 to -34°C (-40 to -30°F) 
Zone 4: -34 to -29°C (-30 to -20°F) 
Zone 5: -29 to -23°C (-20 to -10°F) 
Zone 6: -23 to -18°C (-10 to 0°F) 
Zone 7: -18 to -12°C (0 to 10°F) 
Zone 8: -12 to -7°C (10 to 20°F) 
Zone 9: -7 to -1°C (20 to 30°F) 
Zone 10: -1 to 4°C (30 to 40°F)

© The Heather Society, 29 September 2008