About FrostCal

FrostCal is a free reference for frost dates and planting dates across 4,807 US cities. Look up any ZIP code or city to see when frost typically ends in spring and returns in fall, with no account and no app required.

Why it exists

Most frost-date tools give a single date and stop there. A single date hides the part gardeners actually need: how much risk you're taking by planting on it. FrostCal shows three dates for every location: a typical date, a safer date, and a riskier one. Each comes from 30 years of weather records, so you can decide how much risk to take with tender plants.

Where the data comes from

• Frost dates and temperatures: NOAA National Centers for Environmental Information, 1991–2020 U.S. Climate Normals. Every city page names the weather station it uses and how far away it is.
• Hardiness zones: the USDA 2023 Plant Hardiness Zone Map.
• Places: GeoNames, used under CC BY 4.0.
• Planting windows: timing rules for 42 crops based on university extension guidelines, applied to each city's own frost dates.

The methodology page explains how stations are matched to cities and how the probability ranges work.

How the site is maintained

Pages are generated directly from the data above, so every city uses the same method and nothing is copied by hand. The site is rebuilt monthly. The underlying climate normals are revised by NOAA once a decade; the next release (2001–2030) will be adopted when it's published.

Independence

FrostCal is an independent project. It is not affiliated with NOAA, the USDA, or any seed or garden company. The site is free to use and is supported by advertising.

Corrections

If a date looks wrong for your area, or your town is missing, email twoface692@gmail.com. Microclimates are real: a valley, a hilltop, or a spot near a large lake can differ from the nearest station by a week or more, and reports like that help improve the site.