timing
Hardiness zone
Last reviewed 2026-10-04
A hardiness zone is a geographic category based on the average annual extreme minimum temperature for a location. The USDA Plant Hardiness Zone Map divides the United States into 10 degree Fahrenheit zones, with five degree Fahrenheit half zones. The zone helps compare perennial cold tolerance, but it does not determine planting dates by itself.
What it means
A zone describes a long-term temperature pattern, not the weather in one year. Two gardens in the same zone can differ because of elevation, wind, slope, urban heat, soil drainage, and exposure. A plant listed for a zone range may still fail in a particular site for reasons unrelated to winter minimum temperature.
How it affects the garden
Use the zone as one filter when choosing perennial plants, shrubs, and trees. Combine it with light, soil, moisture, mature size, and the plant's actual cultural requirements. For annual vegetables, frost dates and soil temperature are usually more useful for deciding when to sow or transplant. The frost date finder provides a different kind of timing information.
Example
A perennial labeled hardy in zones 5 to 8 is expected to tolerate the typical minimum temperature range represented by those zones. That does not promise survival in a wet site, an exposed container, or an unusually severe cold event.
Common confusion
Hardiness zone is not the same as climate zone, heat zone, or last frost date. It focuses on average annual extreme cold. A last frost date is a seasonal probability estimate used for timing.
Sources
The USDA Plant Hardiness Zone Map defines the zone system and provides the current map.
