Grafton, Ontario climate data is summarized below. Average annual temperatures range from 39.6 °F (low) to 51.9 °F (high). Annual precipitation averages 25.8 Inches. 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 | -22.4 °F | -18.4 °F | 330.2 in. |
| February | -22.9 °F | -18.7 °F | 177.8 in. |
| March | -19.7 °F | -15.9 °F | 1193.8 in. |
| April | -16.6 °F | -12.9 °F | 1778 in. |
| May | -13.7 °F | -9.8 °F | 1778 in. |
| June | -10.6 °F | -6.9 °F | 2082.8 in. |
| July | -8.7 °F | -5 °F | 2362.2 in. |
| August | -8.6 °F | -4.8 °F | 2108.2 in. |
| September | -10.8 °F | -6.7 °F | 1295.4 in. |
| October | -13.8 °F | -10.1 °F | 1397 in. |
| November | -17.1 °F | -13.5 °F | 1168.4 in. |
| December | -20.2 °F | -16.9 °F | 939.8 in. |
| Annual | 39.6 °F | 51.9 °F | 25.77 in. |
| 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 : -10°F to -5°F |
| Current Drought Conditions | Normal |