Understanding Edaphia

USDA Hardiness Zones

A hardiness zone is one climate measure. It is especially useful for perennial winter survival, but annual vegetable timing needs more context.

What the zone measures

USDA Plant Hardiness Zones are based primarily on average annual extreme minimum winter temperature. The “a” and “b” subdivisions represent five-degree Fahrenheit bands within each numbered zone.

What the zone does not measure

The zone does not by itself tell you the last spring frost, first fall frost, summer heat, humidity, rainfall, day length, soil condition, or one correct vegetable planting date.

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