Maynard, Iowa has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 2.3 °C (low) to 13.5 °C (high). Annual precipitation averages 958.1 Millimeters. Maynard is located in USDA Plant Hardiness Zone 5a. The growing season typically runs from the last frost around May 1 - May 10 through the first frost around Oct. 1 - Oct. 10.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -13.3 °C | -3.8 °C | 28.96 mm |
| February | -11.3 °C | -1.4 °C | 29.72 mm |
| March | -4.5 °C | 6 °C | 50.04 mm |
| April | 1.9 °C | 14.2 °C | 97.03 mm |
| May | 8.6 °C | 20.8 °C | 119.38 mm |
| June | 14.7 °C | 26.2 °C | 147.57 mm |
| July | 16.3 °C | 27.7 °C | 129.79 mm |
| August | 14.9 °C | 26.6 °C | 103.12 mm |
| September | 10.2 °C | 23.3 °C | 93.73 mm |
| October | 3.3 °C | 16.1 °C | 70.87 mm |
| November | -3.4 °C | 6.9 °C | 48.51 mm |
| December | -9.6 °C | -0.6 °C | 39.37 mm |
| Annual | 2.3 °C | 13.5 °C | 958.09 mm |
| Average First Frost Date | Oct. 1 - Oct. 10 |
| Average Last Frost Date | May 1 - May 10 |
| Average Days With Frost | 150-180 Days |
| Plant Hardiness Zone | Zone 5a : -28.9°C to -26.1°C |
| Plant Hardiness Zone - 2012 | Zone 4b : -31.7°C to -28.9°C |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |