Castine, Maine has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 36.7 °F (low) to 54.4 °F (high). Annual precipitation averages 48.9 Inches. Castine 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 | 14.1 °F | 30.3 °F | 3.95 in. |
| February | 15.6 °F | 32.4 °F | 3.32 in. |
| March | 22.9 °F | 39.8 °F | 4.04 in. |
| April | 33.2 °F | 51.5 °F | 4.39 in. |
| May | 43.1 °F | 62.7 °F | 3.81 in. |
| June | 52.3 °F | 71.8 °F | 4.23 in. |
| July | 58.4 °F | 77.6 °F | 3.2 in. |
| August | 57.5 °F | 77.0 °F | 3.23 in. |
| September | 50.4 °F | 69.7 °F | 3.93 in. |
| October | 40.3 °F | 57.7 °F | 5.36 in. |
| November | 31.3 °F | 46.4 °F | 4.72 in. |
| December | 21.5 °F | 36.3 °F | 4.7 in. |
| Annual | 36.7 °F | 54.4 °F | 48.88 in. |
| 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 : -15°F to -10°F |
| Plant Hardiness Zone - 2012 | Zone 5b : -15°F to -10°F |
| Current Drought Conditions | Moderate Drought |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |