Hartland, Wisconsin has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 2.7 °C (low) to 13.2 °C (high). Annual precipitation averages 922.5 Millimeters. Hartland 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. 1 - Oct. 10.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -11.4 °C | -2.7 °C | 44.45 mm |
| February | -9.9 °C | -0.6 °C | 41.15 mm |
| March | -4.6 °C | 5.7 °C | 52.83 mm |
| April | 1.6 °C | 12.9 °C | 96.77 mm |
| May | 7.7 °C | 19.4 °C | 104.39 mm |
| June | 13.2 °C | 24.8 °C | 120.14 mm |
| July | 15.9 °C | 27.3 °C | 104.9 mm |
| August | 15 °C | 26.3 °C | 97.54 mm |
| September | 10.5 °C | 22.5 °C | 81.79 mm |
| October | 4.2 °C | 15.3 °C | 73.91 mm |
| November | -1.9 °C | 7.3 °C | 54.36 mm |
| December | -7.8 °C | 0.4 °C | 50.29 mm |
| Annual | 2.7 °C | 13.2 °C | 922.52 mm |
| Average First Frost Date | Oct. 1 - Oct. 10 |
| 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 5a : -28.9°C to -26.1°C |
| Current Drought Conditions | Moderate Drought |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |