Fall crops race the calendar. The question is simple: what is the latest day I can sow and still have the crop reach maturity before the first fall freeze?
The formula
Last sowing date = first fall freeze date - days to maturity - buffer.
- Days to maturity comes from the seed packet.
- The buffer accounts for slower growth as days shorten and nights cool. Several extension guides suggest adding about two weeks. We use 14 days by default, and the workbook lets you change it.
- Frost-tender crops that stop growing at the first freeze, such as bush beans, deserve a longer buffer.
A worked example
Suppose your station's median first fall freeze at 32F is October 25. A bush bean packet says 55 days to maturity. With a 14-day buffer for the fall slowdown and another 14 days because beans are frost-tender, the count is 55 + 14 + 14 = 83 days back: sow by about August 3.
A hardy crop with 45 days to maturity, such as a turnip, needs 45 + 14 = 59 days: sow by about August 27.
Sowing windows, not single dates
Our products show a window of about three weeks ending at that last sowing date, so there is room for succession sowings. Sowing earlier in the window gives larger plants before the cold; sowing later gives a smaller margin.
Choose your risk level
The earlier (cautious) fall date gives a safer, earlier last-sowing date. The median is a middle path. The later (optimistic) date assumes the freeze comes late.
What about hot weather?
Late summer heat can slow germination of cool-season crops. Seed packets and extension guides cover tricks such as shading and watering for your area.
The first fall freeze date is a historical 1991-2020 statistic from NOAA, not a forecast. Offsets and windows are generic planning defaults, not agricultural advice. Check the current weather forecast as the date approaches.
Want the dates for your own station? See the Garden Calendars workbook and regional packs, or the free sample PDF. Next guide: Your yard is not the weather station: microclimates and frost dates.
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.