Castleton, Vermont has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 35.8 °F (low) to 56.7 °F (high). Annual precipitation averages 41.4 Inches. 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 | 11.0 °F | 29.5 °F | 2.75 in. |
| February | 11.8 °F | 32.3 °F | 2.13 in. |
| March | 21.7 °F | 41.3 °F | 2.82 in. |
| April | 33.2 °F | 56.4 °F | 3.25 in. |
| May | 44.8 °F | 68.5 °F | 3.65 in. |
| June | 54.2 °F | 77.3 °F | 4.37 in. |
| July | 59.0 °F | 81.7 °F | 4.45 in. |
| August | 57.5 °F | 80.1 °F | 4.14 in. |
| September | 49.4 °F | 72.8 °F | 3.55 in. |
| October | 38.5 °F | 59.0 °F | 4.06 in. |
| November | 29.3 °F | 46.3 °F | 3.04 in. |
| December | 19.0 °F | 35.1 °F | 3.19 in. |
| Annual | 35.8 °F | 56.7 °F | 41.4 in. |
| 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 : -20°F to -15°F |
| Plant Hardiness Zone - 2012 | Zone 5a : -20°F to -15°F |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |