Dedham, Maine has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 2.9 °C (low) to 11.1 °C (high). Annual precipitation averages 1177.8 Millimeters. Dedham is located in USDA Plant Hardiness Zone 5a. 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 | -10.6 °C | -3.8 °C | 91.19 mm |
| February | -9.9 °C | -1.4 °C | 73.15 mm |
| March | -6.4 °C | 3.2 °C | 97.79 mm |
| April | 1.3 °C | 9.9 °C | 103.38 mm |
| May | 7.4 °C | 16.4 °C | 92.71 mm |
| June | 12.6 °C | 21.4 °C | 100.58 mm |
| July | 16 °C | 24.7 °C | 84.84 mm |
| August | 15.3 °C | 24.3 °C | 86.36 mm |
| September | 11.1 °C | 20.1 °C | 95.76 mm |
| October | 5 °C | 13.1 °C | 127 mm |
| November | -0.7 °C | 5.8 °C | 110.49 mm |
| December | -6.8 °C | -0.4 °C | 114.55 mm |
| Annual | 2.9 °C | 11.1 °C | 1177.8 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 5a : -28.9°C to -26.1°C |
| Plant Hardiness Zone - 2012 | Zone 5a : -28.9°C to -26.1°C |
| Current Drought Conditions | Abnormally Dry |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |