Grafton, Ontario climate data is summarized below. Average annual temperatures range from 4.2 °C (low) to 11.1 °C (high). Annual precipitation averages 654 Millimeters. Grafton is located in USDA Plant Hardiness Zone 6a. 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 | -8.27 °C | -1.14 °C | 13 mm |
| February | -9.17 °C | -1.71 °C | 7 mm |
| March | -3.51 °C | 3.33 °C | 47 mm |
| April | 2.16 °C | 8.77 °C | 70 mm |
| May | 7.4 °C | 14.39 °C | 70 mm |
| June | 12.91 °C | 19.57 °C | 82 mm |
| July | 16.28 °C | 23.02 °C | 93 mm |
| August | 16.44 °C | 23.28 °C | 83 mm |
| September | 12.54 °C | 19.87 °C | 51 mm |
| October | 7.16 °C | 13.75 °C | 55 mm |
| November | 1.26 °C | 7.68 °C | 46 mm |
| December | -4.36 °C | 1.55 °C | 37 mm |
| Annual | 4.2 °C | 11.1 °C | 654 mm |
| Average First Frost Date | Oct. 1 - Oct. 10 |
| Average Last Frost Date | May 1 - May 10 |
| Average Days With Frost | 125-150 Days |
| Plant Hardiness Zone | Zone 6a : -23.3°C to -20.6°C |
| Current Drought Conditions | Normal |