Harrow, Ontario climate data is summarized below. Average annual temperatures range from 6.3 °C (low) to 13.4 °C (high). Annual precipitation averages 522 Millimeters. Harrow is located in USDA Plant Hardiness Zone 7a. The growing season typically runs from the last frost around Apr. 21 - Apr. 30 through the first frost around Oct. 21 - Oct. 31.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -6.83 °C | -0.9 °C | 20 mm |
| February | -7.59 °C | -0.98 °C | 11 mm |
| March | -1.71 °C | 6 °C | 42 mm |
| April | 4.03 °C | 12.34 °C | 52 mm |
| May | 10.47 °C | 18.96 °C | 60 mm |
| June | 16.44 °C | 24.19 °C | 65 mm |
| July | 18.94 °C | 26.67 °C | 61 mm |
| August | 18.48 °C | 25.89 °C | 60 mm |
| September | 14.29 °C | 22.06 °C | 50 mm |
| October | 8.63 °C | 15.69 °C | 35 mm |
| November | 2.46 °C | 8.66 °C | 39 mm |
| December | -2.5 °C | 2.33 °C | 27 mm |
| Annual | 6.3 °C | 13.4 °C | 522 mm |
| Average First Frost Date | Oct. 21 - Oct. 31 |
| Average Last Frost Date | Apr. 21 - Apr. 30 |
| Average Days With Frost | 100-125 Days |
| Plant Hardiness Zone | Zone 7a : -17.8°C to -15°C |
| Current Drought Conditions | Normal |