USDA plant hardiness zone

USDA Plant Hardiness Zones are areas in North America categorized according to their lowest winter temperatures. The current map was revised and published by the United States Department of Agriculture (USDA) in 1990 and can be used as a guideline for categorizing locations suitable for growing a particular annual plant variety.

The temperatures are referred to as "average annual minimum temperatures" and are based on the lowest temperatures recorded for each of the years 1974 to 1986 in the United States and Canada and 1971 to 1984 in Mexico. The map shows 10 different zones, each of which represents an area of winter hardiness for the plants of agriculture and our natural landscape. The lastest version also introduces zone 11 to represent areas that have average annual minimum temperatures above 40°F (4.4°C) and that are therefore essentially frost free.

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