About and sources

Frost Window gives the average last spring frost and first fall frost for 3,206 US places with 10,000 or more people, and the planting dates that go with them.

Frost dates

From NOAA's U.S. Climate Normals, 1991–2020, published by the NOAA National Centers for Environmental Information. For each weather station, NOAA gives the dates by which the last spring frost (32°F) has passed in 9, 5 and 1 out of 10 years, and the same for the first fall frost, plus the chance of any 32°F night in a year. Each place uses the nearest station with these records; we name it, with its distance and elevation, on the place page. Places more than 50 miles from such a station get no page. A station can sit in a colder valley or a warmer city center than your garden, so treat the dates as a guide.

Planting dates

From USDA Home and Garden Bulletin No. 9 (1967), “Suburban and Farm Vegetable Gardens”: table 4, “Earliest dates, and range of dates, for safe spring planting of vegetables in the open,” and table 5, “Latest dates, and range of dates, for safe fall planting.” USDA lists dates for places whose average last freeze is January 30, February 8 and so on to June 10, and whose average first freeze is August 30 to December 20. For each place we use the column nearest its NOAA average date, within 15 days; outside that, we give no planting dates. We transcribed the tables from the scanned bulletin and checked every cell against it. Where the bulletin repeats the row above (“do.”), we do too. The table is from 1967 and is the published federal table; newer advice from your state's extension service may differ.

Places and ZIP codes

From the US Census Bureau: 2024 Gazetteer files (place and ZIP code area coordinates) and Vintage 2024 population estimates.

What we don't do

No forecasts, no AI-written advice, no ads. Every date on the site comes from one of the sources above.

Who runs it

Frost Window is operated by JY Concepts, New York, USA. Spotted a wrong date? Please tell us.