Harrowsmith, Ontario climate data is summarized below. Average annual temperatures range from 2.3 °C (low) to 12.3 °C (high). Annual precipitation averages 559 Millimeters. 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 | -12.39 °C | -3.07 °C | 9 mm |
| February | -13.12 °C | -3.18 °C | 4 mm |
| March | -6.69 °C | 3.63 °C | 38 mm |
| April | 1.46 °C | 12.07 °C | 60 mm |
| May | 8.09 °C | 19.91 °C | 63 mm |
| June | 13.23 °C | 24.13 °C | 71 mm |
| July | 15.74 °C | 26.73 °C | 78 mm |
| August | 14.93 °C | 25.8 °C | 72 mm |
| September | 10.2 °C | 21.13 °C | 51 mm |
| October | 4.77 °C | 13.87 °C | 53 mm |
| November | -1.21 °C | 7.1 °C | 37 mm |
| December | -7.64 °C | -0.22 °C | 23 mm |
| Annual | 2.3 °C | 12.3 °C | 559 mm |
| 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 : -26.1°C to -23.3°C |
| Current Drought Conditions | Normal |