Frost dates by hardiness zone
A hardiness zone is a band of winter lows, not a frost date. Here is the real spread of NOAA median frost dates across the 6,712 stations matched to each 2023 USDA zone. Your ZIP code gives a closer answer than your zone.
| Zone | Avg. coldest night | ZIP codes | Stations (with frost dates) | Median last spring frost (10th–90th pct) | Median first fall frost | States |
|---|---|---|---|---|---|---|
| Zone 1a | -60 to -55°F | 5 | 1 (1) | too few stations | too few stations | 1 |
| Zone 1b | -55 to -50°F | 11 | 5 (2) | too few stations | too few stations | 1 |
| Zone 2a | -50 to -45°F | 27 | 11 (9) | too few stations | too few stations | 1 |
| Zone 2b | -45 to -40°F | 17 | 10 (6) | too few stations | too few stations | 1 |
| Zone 3a | -40 to -35°F | 23 | 8 (4) | too few stations | too few stations | 2 |
| Zone 3b | -35 to -30°F | 230 | 75 (73) | May 19 (May 14–May 31) | Sep 22 | 5 |
| Zone 4a | -30 to -25°F | 814 | 256 (244) | May 14 (May 7–May 25) | Sep 27 | 15 |
| Zone 4b | -25 to -20°F | 1,284 | 376 (354) | May 11 (May 3–May 31) | Sep 30 | 15 |
| Zone 5a | -20 to -15°F | 2,426 | 602 (577) | May 9 (Apr 28–May 29) | Oct 2 | 18 |
| Zone 5b | -15 to -10°F | 2,880 | 574 (555) | May 4 (Apr 22–May 26) | Oct 8 | 26 |
| Zone 6a | -10 to -5°F | 5,187 | 779 (763) | May 1 (Apr 18–May 23) | Oct 14 | 28 |
| Zone 6b | -5 to 0°F | 5,271 | 749 (736) | Apr 24 (Apr 10–May 16) | Oct 20 | 31 |
| Zone 7a | 0 to 5°F | 4,877 | 738 (732) | Apr 18 (Apr 6–May 9) | Oct 23 | 31 |
| Zone 7b | 5 to 10°F | 3,855 | 500 (500) | Apr 7 (Mar 31–Apr 23) | Oct 31 | 25 |
| Zone 8a | 10 to 15°F | 3,430 | 546 (546) | Mar 30 (Mar 20–Apr 11) | Nov 6 | 21 |
| Zone 8b | 15 to 20°F | 3,379 | 560 (560) | Mar 19 (Mar 8–Apr 16) | Nov 12 | 18 |
| Zone 9a | 20 to 25°F | 2,199 | 363 (363) | Mar 4 (Feb 15–Mar 30) | Nov 25 | 13 |
| Zone 9b | 25 to 30°F | 2,085 | 278 (277) | Feb 4 (Jan 14–Mar 4) | Dec 13 | 8 |
| Zone 10a | 30 to 35°F | 1,234 | 133 (127) | Jan 19 (Jan 4–Feb 13) | Jan 2 | 5 |
| Zone 10b | 35 to 40°F | 752 | 55 (22) | frost rare | frost rare | 2 |
| Zone 11a | 40 to 45°F | 205 | 19 (1) | frost rare | frost rare | 3 |
| Zone 11b | 45 to 50°F | 16 | 11 (0) | frost rare | frost rare | 2 |
| Zone 12a | 50 to 55°F | 30 | 6 (0) | frost rare | frost rare | 1 |
| Zone 12b | 55 to 60°F | 137 | 38 (1) | frost rare | frost rare | 2 |
| Zone 13a | 60 to 65°F | 102 | 16 (0) | frost rare | frost rare | 2 |
| Zone 13b | 65 to 70°F | 26 | 3 (0) | frost rare | frost rare | 2 |
Zones with too few stations (Alaska and the far north) list each station’s own dates instead of a median. In the warmest zones most stations rarely or never reach 32°F.
How these numbers are made
Each ZIP code gets one zone from the USDA-ARS / PRISM 2023 ZIP tables, which use the map’s 1991–2020 average of the coldest winter night of each year. A ZIP code can span more than one zone, and USDA’s own lookup works by ZIP or address. Each NOAA station is assigned the most common zone among the closest ZIP codes listed on its station page (a tie goes to the zone of the closest of those ZIPs). Frost dates are NOAA’s 50%-probability (median) 32°F dates for each station, the same values shown on the station pages. Zone figures are the median, 10th and 90th percentile across stations; a first fall frost in January to June is counted in the following year.
Not the official USDA Plant Hardiness Zone Map. Zones shown here are the values published in the USDA-ARS / Oregon State University PRISM Group 2023 ZIP code tables, shown unaltered. For the official interactive map, visit planthardiness.ars.usda.gov.
Sources
- USDA Agricultural Research Service and PRISM Group, Oregon State University, 2023 Plant Hardiness Zone Map ZIP code tables (CONUS, Alaska, Hawaii, Puerto Rico), files dated November 17, 2023. Data © PRISM Group, Oregon State University, https://prism.oregonstate.edu, accessed November 1, 2026. Official map: planthardiness.ars.usda.gov.
- NOAA National Centers for Environmental Information, U.S. Climate Normals 1991–2020, annual/seasonal normals by station (version 1.0.1), file dated June 27, 2023; documentation.
- U.S. Census Bureau, 2024 Gazetteer ZIP Code Tabulation Areas file, dated August 30, 2024 (ZIP centroids used to find the nearest station).
Freeze dates are 30-year probabilities, not forecasts. Check your local forecast before planting tender plants.