Hartford, Maine has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 1.2 °C (low) to 12.2 °C (high). Annual precipitation averages 1322.1 Millimeters. Hartford 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 | -12.7 °C | -2.6 °C | 92.46 mm |
| February | -12.1 °C | -1.1 °C | 88.39 mm |
| March | -6.7 °C | 3.8 °C | 101.6 mm |
| April | -0.2 °C | 11.1 °C | 117.09 mm |
| May | 6 °C | 18.2 °C | 101.85 mm |
| June | 11.2 °C | 22.9 °C | 138.18 mm |
| July | 14.3 °C | 25.9 °C | 102.11 mm |
| August | 13.3 °C | 25.4 °C | 104.9 mm |
| September | 8.8 °C | 21.3 °C | 93.22 mm |
| October | 3 °C | 13.9 °C | 147.83 mm |
| November | -2.4 °C | 6.9 °C | 114.3 mm |
| December | -8.2 °C | 0.7 °C | 120.14 mm |
| Annual | 1.2 °C | 12.2 °C | 1322.07 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 5a : -28.9°C to -26.1°C |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |