Growing regions designated by the US Department of Agriculture (USDA) which divides the United States and southern Canada into 11 planting zones based on a 10 degree Fahrenheit difference in the average annual minimum temperatures. Using these zones as a guide, seed companies and nurseries label their horticultural products based on which zones plants will grow most successfully in. Higher numbered zones are generally warmer.
Also see: Get Into Your Growing Zone - USDA Plant Hardiness Zones Explained
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