Castine, Maine has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 2.6 °C (low) to 12.5 °C (high). Annual precipitation averages 1241.6 Millimeters. 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 | -9.9 °C | -0.9 °C | 100.33 mm |
| February | -9.1 °C | 0.2 °C | 84.33 mm |
| March | -5.1 °C | 4.3 °C | 102.62 mm |
| April | 0.7 °C | 10.8 °C | 111.51 mm |
| May | 6.2 °C | 17.1 °C | 96.77 mm |
| June | 11.3 °C | 22.1 °C | 107.44 mm |
| July | 14.7 °C | 25.3 °C | 81.28 mm |
| August | 14.2 °C | 25 °C | 82.04 mm |
| September | 10.2 °C | 20.9 °C | 99.82 mm |
| October | 4.6 °C | 14.3 °C | 136.14 mm |
| November | -0.4 °C | 8 °C | 119.89 mm |
| December | -5.8 °C | 2.4 °C | 119.38 mm |
| Annual | 2.6 °C | 12.5 °C | 1241.55 mm |
| 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 : -26.1°C to -23.3°C |
| Plant Hardiness Zone - 2012 | Zone 5b : -26.1°C to -23.3°C |
| Current Drought Conditions | Abnormally Dry |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |