Garretts Mill, Maryland has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 6.5 °C (low) to 18.4 °C (high). Annual precipitation averages 1078.5 Millimeters. Garretts Mill is located in USDA Plant Hardiness Zone 7a. The growing season typically runs from the last frost around Apr. 11 - Apr. 20 through the first frost around Oct. 11 - Oct. 20.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -4.6 °C | 5.2 °C | 79.76 mm |
| February | -3.8 °C | 7.1 °C | 61.21 mm |
| March | -0.1 °C | 11.8 °C | 90.93 mm |
| April | 5.4 °C | 18.6 °C | 86.11 mm |
| May | 10.8 °C | 23.6 °C | 108.97 mm |
| June | 15.8 °C | 28.1 °C | 99.82 mm |
| July | 18.2 °C | 30.7 °C | 103.38 mm |
| August | 17.2 °C | 29.7 °C | 83.82 mm |
| September | 13.3 °C | 25.9 °C | 112.27 mm |
| October | 6.9 °C | 19.8 °C | 86.36 mm |
| November | 1.4 °C | 13.2 °C | 79.25 mm |
| December | -2.5 °C | 7.4 °C | 86.61 mm |
| Annual | 6.5 °C | 18.4 °C | 1078.49 mm |
| Average First Frost Date | Oct. 11 - Oct. 20 |
| Average Last Frost Date | Apr. 11 - Apr. 20 |
| Average Days With Frost | 100-125 Days |
| Plant Hardiness Zone | Zone 7a : -17.8°C to -15°C |
| Plant Hardiness Zone - 2012 | Zone 6b : -20.6°C to -17.8°C |
| Current Drought Conditions | Moderate Drought |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |