Lanark, Ontario climate data is summarized below. Average annual temperatures range from 1.3 °C (low) to 12 °C (high). Annual precipitation averages 741 Millimeters. Lanark is located in USDA Plant Hardiness Zone 5a. The growing season typically runs from the last frost around May 11 - May 20 through the first frost around Sep. 21 - Sep. 30.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -13.54 °C | -3.99 °C | 5 mm |
| February | -13.64 °C | -3.47 °C | 3 mm |
| March | -7.62 °C | 2.85 °C | 25 mm |
| April | 0.56 °C | 12.04 °C | 60 mm |
| May | 7.21 °C | 19.97 °C | 80 mm |
| June | 12.38 °C | 23.98 °C | 119 mm |
| July | 14.52 °C | 26.48 °C | 138 mm |
| August | 13.62 °C | 25.59 °C | 114 mm |
| September | 9.02 °C | 21.05 °C | 77 mm |
| October | 3.88 °C | 13.68 °C | 64 mm |
| November | -2.1 °C | 6.62 °C | 34 mm |
| December | -9.03 °C | -1.36 °C | 22 mm |
| Annual | 1.3 °C | 12 °C | 741 mm |
| Average First Frost Date | Sep. 21 - Sep. 30 |
| Average Last Frost Date | May 11 - May 20 |
| Average Days With Frost | 150-180 Days |
| Plant Hardiness Zone | Zone 5a : -28.9°C to -26.1°C |
| Current Drought Conditions | Normal |