Shakespeare famously wrote "what's past is prologue." In gardening, the use of historical temperature data can offer glimpses of the future and provide the basis for sound decision making. Two uses of historical temperature data in gardening are highlighted below.
The dates of the last freezing temperatures of the spring and the first freezing temperatures of the fall are of great importance to home gardeners, commercial horticulture, farmers, agribusiness, and others. These dates are sometimes referred to as "last frost" and "first frost".
Accurate long-range forecasts of freeze dates remain beyond the reach of science. Therefore, we rely on past temperature observations to calculate the historical probability of freezing temperatures occurring after (spring) or before (autumn) certain dates. Users evaluate these probabilities to make decisions based on their tolerance for risk.
View Freeze/Frost Date Probability Tables
The 2012 USDA Plant Hardiness Zone Map is the standard by which gardeners and growers can determine which plants are most likely to thrive at a location.
Hardiness zones are based on the average annual extreme minimum temperature during a 30-year period in the past, not the lowest temperature that has ever occurred in the past or might occur in the future. Gardeners should keep that in mind when selecting plants, especially if they choose to "push" their hardiness zone by growing plants not rated for their zone.
View Plant Hardiness Zone Maps
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