Frost dates for Birch Hill Dam, MA
At Birch Hill Dam, the median last spring frost (32°F) is May 6 and the median first fall frost is Oct 1, for a typical growing season of 148 days. For a 90% chance that the last frost has passed, wait until May 19. Nearby ZIP codes are in USDA hardiness zone 5b.
- May 6Last spring frost (median)50% chance of 32°F after this date
- May 19Safer planting date10% chance of 32°F after this date
- Oct 1First fall frost (median)50% chance of 32°F by this date
- 148 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 | May 5 | May 19 | Jun 3 |
| 32°F | Apr 25 | May 6 | May 19 |
| 28°F | Apr 10 | Apr 23 | May 5 |
| 24°F | Mar 31 | Apr 9 | Apr 22 |
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 | Sep 9 | Sep 23 | Oct 4 |
| 32°F | Sep 19 | Oct 1 | Oct 16 |
| 28°F | Sep 29 | Oct 12 | Oct 31 |
| 24°F | Oct 7 | Oct 25 | Nov 11 |
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 | 106 days | 126 days | 145 days |
| 32°F | 131 days | 148 days | 166 days |
| 28°F | 152 days | 172 days | 193 days |
| 24°F | 177 days | 198 days | 219 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 |
|---|---|---|---|
| 01436 | 5b | -15 to -10°F | 4 km |
| 01475 | 5b | -15 to -10°F | 7 km |
| 01438 | 5b | -15 to -10°F | 11 km |
| 01468 | 5b | -15 to -10°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 USC00190666, at 42.6325, -72.1228, elevation 261 m (855 ft).
- Data quality: Representative (10+ years), 24 years of freeze data.
- Average days per year at or below 32°F: 178.
- Frost risk changes over short distances. Valleys and low spots freeze earlier than hillsides and city centers.
Nearby weather stations
- Tully Lake (8 km)
- Orange Muni Airport (15 km)
- Ashburnham N (16 km)
- Ashburnham (17 km)
- Barre Falls Dam (24 km)
- Fitchburg COOP (26 km)
- Fitchburg Muni Airport (31 km)
- Leverett #2 (39 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.