Sources and method
Public data from NOAA, the USDA and the U.S. Census Bureau, and planting windows in our own words.
- Frost dates
- NOAA NCEI U.S. Climate Normals 1991–2020
- Hardiness zones
- USDA Plant Hardiness Zone Map (2023), PRISM Climate Group, Oregon State University
- ZIP locations
- U.S. Census Bureau ZCTA Gazetteer
- Your data
- Stays on your device. No account.
Frost dates
Frost dates come from the U.S. Climate Normals 1991–2020 of NOAA's National Centers for Environmental Information: for each weather station, the dates of a 32 °F frost in spring and fall. The last spring frost is the median date, so in half of all years the last frost comes later; the site also gives the date that frost is over by in 9 of 10 years. The first fall frost works the same way, and in a few mild places it falls in early January of the next year.
Which weather station
For each ZIP code the site picks a nearby weather station with a similar climate: among the stations within 30 miles, the closest one, where every half-zone step between the station's hardiness zone and the ZIP code's beyond the first counts as 15 extra miles. That way a valley town is not given a mountain station's dates. With no station within 30 miles, the closest station anywhere is used, and when it is more than 50 miles away the calendar says so.
Where frost is rare
In the warmest places, from zone 10a up, many weather stations go most years without a freeze. When the station chosen for such a ZIP code is one of them, or every station nearby is, the site says frost is rare and suggests planting by the seasons instead of frost dates.
Hardiness zones
Zones come from the USDA Plant Hardiness Zone Map (2023), with the ZIP code file from the PRISM Climate Group, Oregon State University. A zone is the average coldest winter night, in 5 °F bands. The map covers the lower 48 states and DC here; Alaska, Hawaii and Puerto Rico are not covered yet.
ZIP code locations
Each ZIP code is placed at the center of its ZIP Code Tabulation Area from the U.S. Census Bureau Gazetteer Files (2023). ZIP codes without an area of their own, such as PO boxes, take a neighboring area's location, and the calendar says so.
Planting windows
When to sow, plant out and pick is counted in weeks from your frost dates, using general garden practice of the kind US extension services publish, written as our own numbers. Frost-tender crops never go out before the median last frost. Where the season is too short for a crop, the calendar says so instead of inventing dates.
Photos and icons
The photographs and the drawn crop icons were generated for this site. They show no real people.