The terms “freeze free period”, “frost-free period”, and “frost free days” are generally synonymous if they are based on a critical air temperature of 32 degrees Fahrenheit (0 degrees Celsius). These terms equate to the expected number of days between the last freezing temperature in spring (January –July) and the first freezing temperature in the fall (August-December). The number of days is based on the probability that the values for the standard “normal” period will be exceeded in 5 years out of 10. In the transactional soils database (NASIS) these numbers are populated in the Component table as the data element ‘frost free days’. In Official Soil Series Descriptions (OSDs) and detailed soil map unit descriptions, the range of numbers (low values and high values only) are displayed as ‘frost-free period.’ For more information see the Climatic Setting section in Part 618 of the National Soil Survey Handbook (NSSH) at: http://soils.usda.gov/technical/handbook/contents/part618.html#00). Also see Part 614 of the NSSH for an example of how frost-free period is shown in the Geographic Setting section of OSDs.
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Freeze Free Period vs Frost Free Days
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