Marathon, Ontario climate data is summarized below. Average annual temperatures range from -2.2 °C (low) to 6.4 °C (high). Annual precipitation averages 554 Millimeters. Marathon is located in USDA Plant Hardiness Zone 3b. The growing season typically runs from the last frost around May 21 - May 31 through the first frost around Sep. 21 - Sep. 30.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -19.23 °C | -8.71 °C | 0 mm |
| February | -19.22 °C | -7.64 °C | 0 mm |
| March | -11.54 °C | -0.6 °C | 0 mm |
| April | -3.91 °C | 5.13 °C | 29 mm |
| May | 3.29 °C | 11.98 °C | 79 mm |
| June | 8 °C | 16.61 °C | 90 mm |
| July | 10.68 °C | 18.03 °C | 86 mm |
| August | 12.27 °C | 19.45 °C | 74 mm |
| September | 8.71 °C | 15.92 °C | 82 mm |
| October | 3.17 °C | 9.58 °C | 76 mm |
| November | -3.75 °C | 2.59 °C | 38 mm |
| December | -15.3 °C | -5.88 °C | 0 mm |
| Annual | -2.2 °C | 6.4 °C | 554 mm |
| Average First Frost Date | Sep. 21 - Sep. 30 |
| Average Last Frost Date | May 21 - May 31 |
| Average Days With Frost | Over 180 Days |
| Plant Hardiness Zone | Zone 3b : -37.2°C to -34.4°C |
| Current Drought Conditions | Normal |