Dedham, Massachusetts has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 4.8 °C (low) to 15.8 °C (high). Annual precipitation averages 1269.8 Millimeters. Dedham is located in USDA Plant Hardiness Zone 6b. The growing season typically runs from the last frost around Apr. 11 - Apr. 20 through the first frost around Oct. 21 - Oct. 31.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -7.3 °C | 2.7 °C | 102.11 mm |
| February | -6.5 °C | 4.1 °C | 89.41 mm |
| March | -2.3 °C | 7.9 °C | 123.95 mm |
| April | 3.3 °C | 14.6 °C | 112.01 mm |
| May | 8.6 °C | 20.4 °C | 93.22 mm |
| June | 13.8 °C | 25.3 °C | 105.92 mm |
| July | 17.2 °C | 28.6 °C | 93.47 mm |
| August | 16.3 °C | 27.7 °C | 97.54 mm |
| September | 12.2 °C | 23.8 °C | 97.54 mm |
| October | 5.9 °C | 17.2 °C | 124.97 mm |
| November | 0.8 °C | 11.3 °C | 105.16 mm |
| December | -3.9 °C | 5.8 °C | 124.46 mm |
| Annual | 4.8 °C | 15.8 °C | 1269.76 mm |
| Average First Frost Date | Oct. 21 - Oct. 31 |
| Average Last Frost Date | Apr. 11 - Apr. 20 |
| Average Days With Frost | 100-125 Days |
| Plant Hardiness Zone | Zone 6b : -20.6°C to -17.8°C |
| Plant Hardiness Zone - 2012 | Zone 6b : -20.6°C to -17.8°C |
| Current Drought Conditions | Moderate Drought |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |