USDA Hardiness Zones for Americans

American gardeners will find these two websites helpful in determining hardiness zones.  If you live within the USA, head to the U.S. National Arboretum Website where you will find a clickable map to zoom in on your region.  At the National Arborday Website you can also search for your USDA Zone by zip code.

USDA Hardiness Zones for Canadians

Canadian gardeners can figure out their USDA Plant Hardiness Zone using this table, to determine which of our Rock Stars® are suitable for your region. We express Zones as a range: for example if you live in Zone 5, make sure the LOWER number in the range equals your Zone or any Zone below yours. A plant rated hardy for Zones 7 to 9 might not survive for you, but one rated for Zones 3 to 9 includes your Zone 5, so it should survive with no problems.


Min. Winter Temp. (°F) 

 Min. Winter Temp. (°C) 


Below -50

 Below -46


-50 to -40

 -46 to -40


 -40 to -30

 -40 to -34


 -30 to -20

 -34 to -29


 -20 to -10

 -29 to -23


 -10 to 0

 -23 to -18


 0 to 10

 -18 to -12


 10 to 20

 -12 to -7


 20 to 30

 -7 to -1

The USDA Plant Hardiness system makes use of the average minimum winter temperature to determine Zone. This does not always correspond with the Agriculture Canada Zone system, so it’s wise to know both for your region. Other factors such as proximity to a building, winter soil moisture and snow cover (or lack of it) can make a big difference from one year to the next. Zones are never 100% accurate and are only meant as a general guide on expected winter survival.