Understanding USDA Hardiness Zones, AHS Heat Zones, and Sunset Climate Zones can be a crucial aspect of successful gardening, particularly when it comes to selecting appropriate plants for your region.
- USDA Hardiness Zones: Developed by the United States Department of Agriculture, this system divides North America into 13 zones based on average minimum winter temperatures. Each zone is further divided into “a” and “b” for more accuracy. Plants are often labeled with the range of zones where they can thrive. However, it’s worth remembering that this system only takes winter cold into account.
- AHS Heat Zones: Developed by the American Horticultural Society, this system considers the average number of days per year a region experiences temperatures over 86°F (30°C), as many plants can’t tolerate excessive heat. There are 12 heat zones. When combined with USDA Hardiness Zones, you get a more complete picture of a plant’s adaptability.
- Sunset Climate Zones: This system, created by Sunset Magazine, is considered the most precise in the USA, especially for the West Coast. It takes into account not just winter cold and summer heat, but also length of growing season, timing and amount of rainfall, winter lows, summer highs, wind, and humidity. It defines 24 zones in the West, 60 across the USA, and more in Canada and Mexico.
Together, these three systems give a comprehensive guide to what can grow in a given location. Using them can help gardeners avoid costly and disappointing mistakes and can lead to healthier, more vibrant gardens.