About When Is the Last Frost

When Is the Last Frost gives every US ZIP code its frost dates and a planting calendar, free.

Data sources

• Frost dates: NOAA National Centers for Environmental Information, U.S. Climate Normals 1991–2020 — freeze (32°F) probability dates for 7,245 stations. Each ZIP code uses the nearest NOAA station. Stations are classed as having a normal frost season, occasional light frost, rare frost, or frost possible in any month, from NOAA's freeze-probability dates and average number of nights at or below 32°F.
• Hardiness zones: derived from the PRISM Climate Group (Oregon State University) data behind the 2023 USDA Plant Hardiness Zone Map, via the open-source frostline project. This is not the official USDA map; check the USDA site for the authoritative zone.
• ZIP code locations and place names: GeoNames postal code data, licensed CC BY 4.0.
• Planting windows: common timing guidance from university extension services, expressed as weeks before or after the frost date.

Limitations

Frost dates are 30-year statistics, not forecasts. Hills, valleys, cities and bodies of water can shift frost by weeks over short distances. Always check the 10-day forecast before planting tender crops.

For exactly how frost dates are matched to ZIP codes and how planting windows are calculated, see the methodology. Questions or corrections: contact us. Data built 2026-11-11.