Table of the USDA Plant Hardiness Zones:

zone          minimum temperature

1           less than - 45°C / - 49°F

2           - 45°C up to - 40°C / - 49°F up to - 40°F

3           - 40°C up to - 34°C / - 40°F up to - 29°F

4           - 34°C up to - 29°C / - 29°F up to - 20°F

5           - 29°C up to - 23°C / - 20°F up to - 9°F

6           - 23°C up to - 18°C / - 9°F up to 0°F

7           - 18°C up to - 12°C / 0°F up to +10°F

8           - 12°C up to - 7°C / + 10°F up to + 19°F

9           - 7°C up to 0°C / + 19°F up to + 32°F

10           0°C up to + 5°C / +32°F up to + 41°F

11           + 5°C up to + 10°C / + 41°F up to + 50°F

12           + 10°C up to +15°C / + 50°F up to + 59°F

The temperature for given zone of each species is only for indication and it always depends on specific conditions of your area - the amount and consistency of precipitation in the winter, the course of spring and autumn weather etc.