Alliston, Ontario climate data is summarized below. Average annual temperatures range from 2.1 °C (low) to 12.5 °C (high). Annual precipitation averages 664 Millimeters. Alliston 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. 11 - Oct. 20.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -10.24 °C | -2.34 °C | 7 mm |
| February | -11.29 °C | -2.75 °C | 0 mm |
| March | -5.78 °C | 4.18 °C | 29 mm |
| April | 0.46 °C | 12.08 °C | 50 mm |
| May | 6.36 °C | 19.61 °C | 79 mm |
| June | 11.7 °C | 24.1 °C | 97 mm |
| July | 14.28 °C | 26.61 °C | 129 mm |
| August | 13.56 °C | 25.64 °C | 117 mm |
| September | 9.32 °C | 21.39 °C | 63 mm |
| October | 4.64 °C | 14.19 °C | 45 mm |
| November | -1.25 °C | 7.35 °C | 29 mm |
| December | -6.18 °C | 0.43 °C | 19 mm |
| Annual | 2.1 °C | 12.5 °C | 664 mm |
| Average First Frost Date | Oct. 11 - Oct. 20 |
| Average Last Frost Date | May 1 - May 10 |
| Average Days With Frost | 125-150 Days |
| Plant Hardiness Zone | Zone 5b : -26.1°C to -23.3°C |
| Current Drought Conditions | Normal |