Plainwell, Michigan has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 3.7 °C (low) to 14.7 °C (high). Annual precipitation averages 1024.1 Millimeters. Plainwell is located in USDA Plant Hardiness Zone 6a. 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 | -8 °C | -0.1 °C | 77.47 mm |
| February | -7.8 °C | 1.3 °C | 55.37 mm |
| March | -3.7 °C | 7.2 °C | 61.72 mm |
| April | 2.2 °C | 14.6 °C | 94.74 mm |
| May | 8.3 °C | 20.9 °C | 109.47 mm |
| June | 13.2 °C | 25.9 °C | 102.36 mm |
| July | 15.3 °C | 28.1 °C | 92.96 mm |
| August | 14.6 °C | 27.2 °C | 99.57 mm |
| September | 10.4 °C | 23.8 °C | 86.87 mm |
| October | 4.5 °C | 16.5 °C | 99.31 mm |
| November | -0.3 °C | 8.9 °C | 76.96 mm |
| December | -4.8 °C | 2.6 °C | 67.31 mm |
| Annual | 3.7 °C | 14.7 °C | 1024.11 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 6a : -23.3°C to -20.6°C |
| Plant Hardiness Zone - 2012 | Zone 5b : -26.1°C to -23.3°C |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |