Frost dates for Groton, CT
At Groton, the median last spring frost (32°F) is Apr 8 and the median first fall frost is Nov 2, for a typical growing season of 207 days. For a 90% chance that the last frost has passed, wait until Apr 22. Nearby ZIP codes are in USDA hardiness zones 6b to 7a.
- Apr 8Last spring frost (median)50% chance of 32°F after this date
- Apr 22Safer planting date10% chance of 32°F after this date
- Nov 2First fall frost (median)50% chance of 32°F by this date
- 207 daysGrowing season (median)between 32°F freezes
Last spring frost dates
The chance that the temperature drops to the threshold after each date.
| Temperature | 90% chance later | 50% chance later | 10% chance later |
|---|---|---|---|
| 36°F | Apr 10 | Apr 22 | May 5 |
| 32°F | Mar 28 | Apr 8 | Apr 22 |
| 28°F | Mar 14 | Mar 29 | Apr 7 |
| 24°F | Mar 4 | Mar 17 | Mar 31 |
First fall frost dates
The chance that the temperature has dropped to the threshold by each date.
| Temperature | 10% chance by | 50% chance by | 90% chance by |
|---|---|---|---|
| 36°F | Oct 8 | Oct 21 | Nov 4 |
| 32°F | Oct 18 | Nov 2 | Nov 15 |
| 28°F | Nov 1 | Nov 14 | Dec 1 |
| 24°F | Nov 13 | Nov 29 | Dec 14 |
Growing season length
Days between the last spring and first fall freeze, as the length reached in 9, 5 and 1 out of 10 years.
| Temperature | 9 in 10 years at least | 5 in 10 years at least | 1 in 10 years at least |
|---|---|---|---|
| 36°F | 162 days | 181 days | 199 days |
| 32°F | 188 days | 207 days | 226 days |
| 28°F | 212 days | 232 days | 255 days |
| 24°F | 236 days | 256 days | 277 days |
Chance of a freeze in any year
| Temperature | Chance per year |
|---|---|
| 36°F | 100% |
| 32°F | 100% |
| 28°F | 100% |
| 24°F | 100% |
ZIP codes whose closest station is this one
| ZIP | Hardiness zone | Avg. extreme low | Distance |
|---|---|---|---|
| 06340 | 7a | 0 to 5°F | 1 km |
| 06355 | 7a | 0 to 5°F | 6 km |
| 06375 | 7a | 0 to 5°F | 9 km |
| 06335 | 7a | 0 to 5°F | 10 km |
| 06339 | 6b | -5 to 0°F | 11 km |
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.
About this station
- NOAA station ID USC00063207, at 41.3503, -72.0378, elevation 12 m (40 ft).
- Data quality: Representative (10+ years), 24 years of freeze data.
- Average days per year at or below 32°F: 102.
- Frost risk changes over short distances. Valleys and low spots freeze earlier than hillsides and city centers.
Nearby weather stations
- Groton New London Airport (3 km)
- Norwich Public Utility Plant (20 km)
- Willimantic Windham Airport (45 km)
- Hampton (46 km)
- Storrs (52 km)
- Hartford Brainard Field (67 km)
- W Thompson Lake (67 km)
- Meriden Markham Muni Airport (68 km)
Sources
- 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.
- 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.
- 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.