Dennison, Ohio has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 4.7 °C (low) to 16.7 °C (high). Annual precipitation averages 1079.3 Millimeters. Dennison is located in USDA Plant Hardiness Zone 6b. The growing season typically runs from the last frost around Apr. 21 - Apr. 30 through the first frost around Oct. 11 - Oct. 20.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -6.9 °C | 2.5 °C | 79.5 mm |
| February | -6.2 °C | 4.3 °C | 60.2 mm |
| March | -2.1 °C | 9.8 °C | 87.12 mm |
| April | 3.6 °C | 17.2 °C | 97.28 mm |
| May | 9.4 °C | 22.7 °C | 106.68 mm |
| June | 14.2 °C | 27.1 °C | 128.02 mm |
| July | 16.4 °C | 29 °C | 102.11 mm |
| August | 15.4 °C | 28.4 °C | 96.27 mm |
| September | 11.3 °C | 24.9 °C | 86.36 mm |
| October | 5 °C | 18.1 °C | 81.03 mm |
| November | -0.1 °C | 11.2 °C | 75.44 mm |
| December | -3.8 °C | 5.2 °C | 79.25 mm |
| Annual | 4.7 °C | 16.7 °C | 1079.26 mm |
| Average First Frost Date | Oct. 11 - Oct. 20 |
| Average Last Frost Date | Apr. 21 - Apr. 30 |
| Average Days With Frost | 100-125 Days |
| Plant Hardiness Zone | Zone 6b : -20.6°C to -17.8°C |
| Plant Hardiness Zone - 2012 | Zone 6a : -23.3°C to -20.6°C |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |