Castalia, Ohio has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 5.8 °C (low) to 15 °C (high). Annual precipitation averages 988.3 Millimeters. Castalia 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 Nov. 1 - Nov. 10.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -7 °C | 0.7 °C | 66.29 mm |
| February | -6.2 °C | 2.2 °C | 55.37 mm |
| March | -1.9 °C | 7.3 °C | 70.36 mm |
| April | 4.1 °C | 14.3 °C | 99.57 mm |
| May | 10.6 °C | 20.7 °C | 96.01 mm |
| June | 16.2 °C | 25.9 °C | 103.63 mm |
| July | 18.2 °C | 28.1 °C | 98.04 mm |
| August | 17.4 °C | 27.1 °C | 88.39 mm |
| September | 13.5 °C | 23.8 °C | 87.63 mm |
| October | 7.2 °C | 17.3 °C | 79.76 mm |
| November | 1.4 °C | 9.7 °C | 72.39 mm |
| December | -3.6 °C | 3.4 °C | 70.87 mm |
| Annual | 5.8 °C | 15 °C | 988.31 mm |
| Average First Frost Date | Nov. 1 - Nov. 10 |
| 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 6a : -23.3°C to -20.6°C |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |