Growing Season Length by Frost Dates
On this page
For a simple frost-based comparison, count the calendar days from the 50% last spring freeze to the 50% first fall freeze, using the same temperature threshold at both ends. This page uses NOAA's 32 °F freeze dates. It describes the interval between two climate normals; it is not a guarantee of frost-free weather in a particular year.
Example growing-season intervals
| NOAA station | Last spring freeze, 50% | First fall freeze, 50% | Interval |
|---|---|---|---|
| Columbus Port Columbus International Airport, Ohio | Apr 18 | Oct 27 | 192 days |
| Cleveland, Ohio | Apr 20 | Nov 3 | 197 days |
| Austin Bergstrom Airport, Texas | Mar 12 | Nov 16 | 249 days |
The calculation is the date difference, not an inclusive count of both endpoint dates. Columbus, for example, has 192 calendar days between April 18 and October 27. The site calculator finds the interval from the selected NOAA station's 50% dates.
Why the probability level matters
The 50% dates are the middle of the historical distribution. A gardener who wants a more cautious interval can use the 10% last-spring date (later) and 10% first-fall date (earlier). At Columbus, those dates are May 5 and October 14, a shorter interval of 162 days. This gives a bigger buffer against freezes; it does not account for every crop's heat, day-length or maturity needs.
Don't mix probability levels without labeling the choice. The 10% spring date is late and cautious, while the 10% fall date is early and cautious. The frost date guide explains why the order flips between spring and fall.
Use the interval as context
Compare stations only when the threshold and probability level match. A 32 °F freeze interval is different from a 36 °F frost interval, and a 10%-to-10% interval is different from a 50%-to-50% interval. The frost date tool lets you select a nearby station and see the values separately.
NOAA's 1991–2020 normals summarize historical climate at stations. The yard may differ from the station, and the actual dates shift from year to year. Use local forecasts near the edges of your growing plans.
Sources
- NOAA National Centers for Environmental Information, U.S. Climate Normals 1991–2020, annual/seasonal station data.
- NOAA Climate.gov, Last Freeze map, which uses the 50% last-freeze date.