Data and method

What the numbers are, where they come from, and what they cannot tell you. Last verified 2026-10-17.

Frost data

All frost and freeze dates are from the NOAA NCEI U.S. Climate Normals 1991-2020 (Annual/Seasonal, v1.0.1), fetched station by station from NCEI's public files on 2026-10-17. We kept New England stations (CT, MA, ME, NH, RI, VT) whose freeze probability normals are flagged "Standard" (24+ years) or "Representative" (10+ years). Stations NOAA flags as "Estimated" were excluded. 246 stations are included. Variables used: ANN-TMIN-PRBLST (last spring freeze) and ANN-TMIN-PRBFST (first fall freeze) at 28, 32 and 36°F, and ANN-TMIN-PRBGSL (freeze-free season) at 32°F. Definitions: NOAA readme. The raw station data is in stations.json.

Planting schedule rules

Crop timing uses the per-crop rules in UNH Extension's "When to Plant Your Vegetable Garden" fact sheet, read 2026-10-17. The rules are expressed in weeks before or after the last frost. We apply them to the last-32°F-freeze date at the risk level you choose (50%, 30% or 10%). That mapping is our choice, because the UNH sheet does not define which probability its "last frost" means. The sheet is written for New Hampshire; other New England Extensions give similar but not identical guidance (see the directory). If your state's Extension says something different, follow them.

Limits

• Station normals are averages over 1991-2020, not forecasts, and climate is changing.
• A station is a point. Elevation, slope, cold-air drainage, water, pavement and tree cover change your frost dates. UNH Extension says freeze dates can vary between relatively close locations.
• We do not convert ZIP codes to dates. The "use my location" button on the home page runs in your browser only and nothing is sent anywhere.
• Soil temperature is often a better guide than the calendar; use a soil thermometer.

Other tools you may also like

Other sites cover frost dates too. We are one option among several; compare them.

• Old Farmer's Almanac frost dates (ZIP-based, 30% probability threshold, nearest station).
• SeedNana (state pages by NOAA station, with average, "safe" 10% and "early" 90% dates).
• GardenTrack (national NOAA freeze/frost normals CSV).

Corrections

If a date or link is wrong, check it against the source linked next to it. A public corrections contact is being set up. For gardening questions use your state's Extension helpline listed in the directory.