Hardiness zones are geographical regions that help gardeners and landscapers identify which plants are most likely to thrive in their area based on climate conditions, particularly winter temperatures. The concept is primarily based on the lowest average winter temperature a region experiences, which influences a plant's ability to survive cold weather.

The United States Department of Agriculture (USDA) developed the USDA Plant Hardiness Zone Map, which divides the country into 13 zones, ranging from Zone 1 (harsh, extremely cold) to Zone 13 (mild, warm). Each zone is defined by a temperature range, typically in 10-degree Fahrenheit increments, where certain plants can reliably grow.

By consulting the hardiness zones, gardeners can select plants that are well-suited to their local climate, reducing the risk of plant failure due to temperature extremes. Hardiness zones are not only useful for choosing flowering plants, trees, and shrubs but also for understanding the compatibility of fruits and vegetables with the local growing seasons.