A frost-date table gives you two anchor dates for the year. Nearly everything else in a planting calendar is counted from one or the other.
The last spring freeze
This is the date after which a freeze (at your chosen temperature) becomes unlikely. Spring crops that tolerate cold are often planted weeks before it, and tender crops are planted after it. Planting calendars therefore count in weeks relative to this date: minus four weeks, plus two weeks and so on.
The first fall freeze
This is the date by which freezing weather has typically arrived. Fall plans count backwards from it: if a crop needs 60 days to mature, and you add a safety buffer, you subtract those days from the first fall freeze to find the last sensible sowing date.
The freeze-free season
The days between the two dates is the freeze-free season. NOAA publishes its own season-length statistic, which is computed differently from simply subtracting the median dates, so the two numbers can differ by a few days. That is normal.
A freeze-free season is not the whole growing season. Cool-season crops grow before the last spring freeze and after the first fall freeze; warm-season crops need warm soil and warm nights as well.
Mild climates
In parts of Florida, the Gulf coast, southern Texas, Arizona and coastal California freezes are only occasional. A table may show a "last freeze" in January or February and a "first freeze" in December or even the following January. Dates in the cold season are placed in the adjacent calendar year so that spring still comes before fall. Where a station's season is 360 days or more, our products mark it with an asterisk (365*): the dates describe occasional freezes, and many years have none.
Different thresholds
Tables list dates for several temperature thresholds (36F, 32F, 28F, 24F). The same station will have an earlier last 28F date than 32F date in spring, and a later first 28F date in fall. See the guide on the thresholds for what they mean.
Dates are historical 1991-2020 statistics, not a forecast. Always check the current forecast.
Want the dates for your own station? See the Garden Calendars workbook and regional packs, or the free sample PDF. Next guide: 32F, 28F, 24F and 36F: what the freeze thresholds mean in a frost-date table.
Please note. Historical 1991-2020 averages from NOAA; actual frost dates vary year to year; not a forecast or a guarantee; not agricultural advice. Planting windows are generic offsets from historical dates; follow your seed packet, your local extension office and the current weather forecast. This product is AI-assisted, so errors are still possible; please report them to gb1@mail.grokbot.com.
Source: Palecki, M., Durre, I., Applequist, S., Arguez, A., Lawrimore, J. (2021). U.S. Climate Normals 2020: U.S. Annual/Seasonal Climate Normals (1991-2020), version 1.0.1. NOAA National Centers for Environmental Information. doi:10.25921/4ek7-fk11. Quietcog is independent and is not affiliated with, endorsed by or sponsored by NOAA or the National Weather Service. Quietcog processed the station files; any processing errors are ours.
Support: gb1@mail.grokbot.com.