Marlborough, Connecticut has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 4.6 °C (low) to 15.7 °C (high). Annual precipitation averages 1276.4 Millimeters. Marlborough is located in USDA Plant Hardiness Zone 6b. The growing season typically runs from the last frost around Apr. 21 - Apr. 30 through the first frost around Oct. 11 - Oct. 20.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -7.4 °C | 2.4 °C | 95.25 mm |
| February | -6.7 °C | 3.8 °C | 82.55 mm |
| March | -2.5 °C | 8.2 °C | 114.05 mm |
| April | 3.1 °C | 14.9 °C | 109.73 mm |
| May | 8.5 °C | 20.7 °C | 94.49 mm |
| June | 13.7 °C | 25.3 °C | 112.01 mm |
| July | 16.8 °C | 28.2 °C | 102.11 mm |
| August | 16 °C | 27.4 °C | 108.97 mm |
| September | 11.8 °C | 23.6 °C | 114.3 mm |
| October | 5.5 °C | 17.2 °C | 126.24 mm |
| November | 0.2 °C | 11 °C | 100.84 mm |
| December | -4.1 °C | 5.5 °C | 115.82 mm |
| Annual | 4.6 °C | 15.7 °C | 1276.36 mm |
| Average First Frost Date | Oct. 11 - Oct. 20 |
| Average Last Frost Date | Apr. 21 - Apr. 30 |
| Average Days With Frost | 100-125 Days |
| Plant Hardiness Zone | Zone 6b : -20.6°C to -17.8°C |
| Plant Hardiness Zone - 2012 | Zone 6a : -23.3°C to -20.6°C |
| Current Drought Conditions | Moderate Drought |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |