Dedham, Iowa has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 3.1 °C (low) to 14.9 °C (high). Annual precipitation averages 864.9 Millimeters. Dedham is located in USDA Plant Hardiness Zone 5a. The growing season typically runs from the last frost around Apr. 21 - Apr. 30 through the first frost around Oct. 1 - Oct. 10.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -11.9 °C | -2 °C | 20.83 mm |
| February | -9.7 °C | 0.6 °C | 27.18 mm |
| March | -3.7 °C | 8.1 °C | 48.51 mm |
| April | 2.3 °C | 15.6 °C | 90.42 mm |
| May | 9.4 °C | 21.7 °C | 123.7 mm |
| June | 15.3 °C | 27.3 °C | 130.05 mm |
| July | 17.3 °C | 28.9 °C | 102.62 mm |
| August | 15.8 °C | 27.7 °C | 101.35 mm |
| September | 10.6 °C | 24.6 °C | 81.28 mm |
| October | 3.9 °C | 17.3 °C | 68.58 mm |
| November | -3.1 °C | 8.2 °C | 38.35 mm |
| December | -8.7 °C | 0.9 °C | 32 mm |
| Annual | 3.1 °C | 14.9 °C | 864.87 mm |
| Average First Frost Date | Oct. 1 - Oct. 10 |
| Average Last Frost Date | Apr. 21 - Apr. 30 |
| 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 | Moderate Drought |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |