Hardiness Zone Map 2020. Each growing zone is 10°f warmer (or colder) in an average winter than the adjacent zone. The table above shows you the minimum average yearly temperatures.
The new hardiness zone map released this year has been created using gis (geographic information system) to examine hardiness zones at a much finer scale. The usda plant hardiness zone map is the standard by which gardeners and growers can determine which perennial plants are most likely to thrive at a location.