Harrowsmith, Ontario climate data is summarized below. Average annual temperatures range from 36.1 °F (low) to 54.2 °F (high). Annual precipitation averages 22 Inches. Harrowsmith is located in USDA Plant Hardiness Zone 5b. 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 | -24.7 °F | -19.5 °F | 228.6 in. |
| February | -25.1 °F | -19.5 °F | 101.6 in. |
| March | -21.5 °F | -15.8 °F | 965.2 in. |
| April | -17 °F | -11.1 °F | 1524 in. |
| May | -13.3 °F | -6.7 °F | 1600.2 in. |
| June | -10.4 °F | -4.4 °F | 1803.4 in. |
| July | -9 °F | -2.9 °F | 1981.2 in. |
| August | -9.5 °F | -3.4 °F | 1828.8 in. |
| September | -12.1 °F | -6 °F | 1295.4 in. |
| October | -15.1 °F | -10.1 °F | 1346.2 in. |
| November | -18.5 °F | -13.8 °F | 939.8 in. |
| December | -22 °F | -17.9 °F | 584.2 in. |
| Annual | 36.1 °F | 54.2 °F | 22.02 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 5b : -15°F to -10°F |
| Current Drought Conditions | Normal |