Castleton, Vermont has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 2.1 °C (low) to 13.7 °C (high). Annual precipitation averages 1051.6 Millimeters. Castleton is located in USDA Plant Hardiness Zone 5a. 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 | -11.7 °C | -1.4 °C | 69.85 mm |
| February | -11.2 °C | 0.2 °C | 54.1 mm |
| March | -5.7 °C | 5.2 °C | 71.63 mm |
| April | 0.7 °C | 13.6 °C | 82.55 mm |
| May | 7.1 °C | 20.3 °C | 92.71 mm |
| June | 12.3 °C | 25.2 °C | 111 mm |
| July | 15 °C | 27.6 °C | 113.03 mm |
| August | 14.2 °C | 26.7 °C | 105.16 mm |
| September | 9.7 °C | 22.7 °C | 90.17 mm |
| October | 3.6 °C | 15 °C | 103.12 mm |
| November | -1.5 °C | 7.9 °C | 77.22 mm |
| December | -7.2 °C | 1.7 °C | 81.03 mm |
| Annual | 2.1 °C | 13.7 °C | 1051.57 mm |
| Average First Frost Date | Oct. 1 - Oct. 10 |
| Average Last Frost Date | May 1 - May 10 |
| Average Days With Frost | 150-180 Days |
| Plant Hardiness Zone | Zone 5a : -28.9°C to -26.1°C |
| Plant Hardiness Zone - 2012 | Zone 5a : -28.9°C to -26.1°C |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |