Swanzey, New Hampshire has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 1.7 °C (low) to 14 °C (high). Annual precipitation averages 1168.7 Millimeters. Swanzey is located in USDA Plant Hardiness Zone 5b. The growing season typically runs from the last frost around May 11 - May 20 through the first frost around Oct. 1 - Oct. 10.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -11.5 °C | -0.4 °C | 83.06 mm |
| February | -10.8 °C | 1.3 °C | 72.64 mm |
| March | -5.9 °C | 5.9 °C | 86.36 mm |
| April | 0.4 °C | 13.4 °C | 89.66 mm |
| May | 6.4 °C | 19.9 °C | 95 mm |
| June | 11.6 °C | 24.7 °C | 109.47 mm |
| July | 14.4 °C | 27.6 °C | 109.47 mm |
| August | 13.4 °C | 26.7 °C | 105.41 mm |
| September | 8.9 °C | 22.4 °C | 103.89 mm |
| October | 2.9 °C | 15.4 °C | 123.95 mm |
| November | -2.4 °C | 8.6 °C | 89.66 mm |
| December | -7.3 °C | 2.6 °C | 100.08 mm |
| Annual | 1.7 °C | 14 °C | 1168.65 mm |
| Average First Frost Date | Oct. 1 - Oct. 10 |
| Average Last Frost Date | May 11 - May 20 |
| Average Days With Frost | 150-180 Days |
| Plant Hardiness Zone | Zone 5b : -26.1°C to -23.3°C |
| Plant Hardiness Zone - 2012 | Zone 5b : -26.1°C to -23.3°C |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |