hardinesszone

Hardiness zone is a geographic area defined by the average annual minimum winter temperature, used to indicate which plants are capable of withstanding winter conditions in that area. The term is most often associated with the USDA Plant Hardiness Zone Map, which divides the United States and parts of Canada into 1 through 13 zones. Each zone roughly corresponds to a 10-degree Fahrenheit band of minimum winter temperature, with subdivisions a and b for finer tolerance (for example, 5a and 5b). The maps are based on historical climate data and are periodically updated to reflect changing conditions.

Gardeners use hardiness zones to select species and cultivars that can survive winter in their location. A plant labeled as hardy to zone 6, for instance, should tolerate typical winter lows found in zone 6. However, zone alone does not guarantee survival; microclimates such as cold winds, southern exposure, or insulated micro-sites, as well as soil, moisture, and snow cover, can influence outcomes. Additionally, some plants may require winter chill or specific timing of dormancy that a zone map does not capture.

Beyond the USDA system, other regions maintain their own hardiness ratings, such as the Canada Plant Hardiness Index and the Royal Horticultural Society's ratings used in the UK. All systems share the goal of guiding plant selection, while recognizing that real-world survival depends on multiple interacting factors.