What Is a Hardiness Zone?
Using historical temperature data, the USDA has divided the country into 13 hardiness zones, ranging from 1 (coldest) to 13 (warmest). Each of these zones is further divided into “A” and “B” for greater accuracy, with A being colder than B. These zones are defined by average annual minimum temperature. For example, a zip code in which the average annual minimum temperature is between -15 and -10 Fahrenheit is assigned to hardiness zone 5B.
The idea behind the zones is that gardeners can look up their hardiness zone and use it to identify plants which will thrive in their area. For example, a gardener in Northwest Connecticut (hardiness zone 5) will confidently plant a variety that has been rated hardy to zone 4, but would generally not plant a variety that is only rated hardy to zone 6, because the zone 6 plant would not likely survive their typical winter.
