Groton, Massachusetts has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 3.4 °C (low) to 15.3 °C (high). Annual precipitation averages 1224.5 Millimeters. Groton is located in USDA Plant Hardiness Zone 6a. The growing season typically runs from the last frost around May 1 - May 10 through the first frost around Oct. 1 - Oct. 10.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -9.4 °C | 1.2 °C | 90.17 mm |
| February | -8.6 °C | 2.7 °C | 85.34 mm |
| March | -4.1 °C | 7.1 °C | 108.46 mm |
| April | 1.9 °C | 14.5 °C | 100.84 mm |
| May | 7.9 °C | 20.7 °C | 95.5 mm |
| June | 13.3 °C | 25.6 °C | 114.81 mm |
| July | 16.3 °C | 28.7 °C | 93.73 mm |
| August | 15.3 °C | 27.8 °C | 99.82 mm |
| September | 10.8 °C | 23.7 °C | 102.62 mm |
| October | 4.3 °C | 16.7 °C | 121.67 mm |
| November | -1 °C | 10.2 °C | 98.04 mm |
| December | -5.8 °C | 4.3 °C | 113.54 mm |
| Annual | 3.4 °C | 15.3 °C | 1224.54 mm |
| Average First Frost Date | Oct. 1 - Oct. 10 |
| Average Last Frost Date | May 1 - May 10 |
| Average Days With Frost | 125-150 Days |
| Plant Hardiness Zone | Zone 6a : -23.3°C to -20.6°C |
| Plant Hardiness Zone - 2012 | Zone 5b : -26.1°C to -23.3°C |
| Current Drought Conditions | Moderate Drought |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |