Casselman, Ontario climate data is summarized below. Average annual temperatures range from 34.9 °F (low) to 54.5 °F (high). Annual precipitation averages 20.8 Inches. Casselman is located in USDA Plant Hardiness Zone 5a. The growing season typically runs from the last frost around May 1 - May 10 through the first frost around Oct. 1 - Oct. 10.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -25.6 °F | -20.2 °F | 0 in. |
| February | -25.4 °F | -19.8 °F | 0 in. |
| March | -21.9 °F | -16 °F | 431.8 in. |
| April | -17.2 °F | -10.7 °F | 1193.8 in. |
| May | -13.5 °F | -6.3 °F | 1371.6 in. |
| June | -10.5 °F | -3.8 °F | 1930.4 in. |
| July | -9.1 °F | -2.4 °F | 2590.8 in. |
| August | -9.7 °F | -2.9 °F | 2133.6 in. |
| September | -12.4 °F | -5.5 °F | 1651 in. |
| October | -15.5 °F | -9.9 °F | 1320.8 in. |
| November | -18.9 °F | -14 °F | 635 in. |
| December | -22.8 °F | -18.6 °F | 177.8 in. |
| Annual | 34.9 °F | 54.5 °F | 20.84 in. |
| Average First Frost Date | Oct. 1 - Oct. 10 |
| Average Last Frost Date | May 1 - May 10 |
| Average Days With Frost | 150-180 Days |
| Plant Hardiness Zone | Zone 5a : -20°F to -15°F |
| Current Drought Conditions | Normal |