The frost dates in a table are for the weather station's location. Your yard may be earlier or later by days, and sometimes by weeks.
What causes the difference
- Cold-air drainage. On calm, clear nights cold air flows downhill like water and pools at low points. A garden at the bottom of a slope can freeze when the hilltop does not.
- Elevation. Higher ground is generally colder over the season, though not always on a single still night.
- Heat storage. Walls, paving and large rocks release stored warmth at night, and a south-facing wall can protect plants nearby.
- Water. Large lakes and the ocean moderate temperatures, delaying fall freezes and sometimes spring warming.
- Cities. Dense areas often stay warmer overnight than the surrounding countryside.
- Cover. Row cover, a cold frame or a tree canopy can all change what plants experience.
Simple ways to learn your yard
- Put an inexpensive min-max thermometer in the bed and write down the overnight low during the shoulder seasons.
- Note the first and last dates when frost shows on the ground, the car or the lawn.
- Compare your numbers with your nearest NOAA station and its neighbours, then record the difference.
- After two or three seasons you can shift the table by your own offset.
The Garden Journal has a freeze-event log and an observations log for this.
Using it with the tables
If your yard runs colder than the station, lean toward the cautious (10%) spring date and the cautious fall date. If it runs warmer, the median may be enough. Either way, treat the table as a starting point.
The dates are historical 1991-2020 statistics from NOAA station records. They are not a forecast or a guarantee.
Want the dates for your own station? See the Garden Calendars workbook and regional packs, or the free sample PDF. Next guide: What "10%, 50% and 90%" mean on 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.