There are 11 USDA hardiness zones. Idaho's USDA hardiness zone will vary, depending on where you live in the valley. For the Boise, Idaho area where we are located, our USDA hardiness zone is 6b. That's from -5 degrees below zero to 0 degrees. Some feel we belong in zone 7 while others feel USDA hardiness should be zone 5. In part, the particular part of town you live in may make a difference on your hardiness zone. Add to that, some gardening folks have great protection from the elements while others have little protection.
USDA HARDINESS ZONE
Fahrenheit
Zone 1 Below -50 Zone 6 -10 to -0
Zone 2 -50 to -40 Zone 7 0 to 10
Zone 3 -40 to -30 Zone 8 10 to 20
Zone 4 -30 to -20 Zone 9 20 to 20
Zone 5 -20 to -10 Zone 10 30 to 40