Grasston, Minnesota has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 31.5 °F (low) to 53.2 °F (high). Annual precipitation averages 31.3 Inches. Grasston is located in USDA Plant Hardiness Zone 4a. The growing season typically runs from the last frost around May 1 - May 10 through the first frost around Sep. 21 - Sep. 30.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 1.2 °F | 21.4 °F | 0.71 in. |
| February | 4.7 °F | 26.8 °F | 0.85 in. |
| March | 17.6 °F | 39.2 °F | 1.53 in. |
| April | 30.6 °F | 53.6 °F | 2.74 in. |
| May | 43.1 °F | 67.0 °F | 3.87 in. |
| June | 53.7 °F | 76.5 °F | 4.43 in. |
| July | 58.0 °F | 80.8 °F | 4.37 in. |
| August | 55.3 °F | 78.8 °F | 3.97 in. |
| September | 46.8 °F | 70.7 °F | 3.19 in. |
| October | 34.8 °F | 56.3 °F | 2.94 in. |
| November | 22.5 °F | 40.0 °F | 1.61 in. |
| December | 9.5 °F | 26.7 °F | 1.12 in. |
| Annual | 31.5 °F | 53.2 °F | 31.33 in. |
| Average First Frost Date | Sep. 21 - Sep. 30 |
| Average Last Frost Date | May 1 - May 10 |
| Average Days With Frost | 150-180 Days |
| Plant Hardiness Zone | Zone 4a : -30°F to -25°F |
| Plant Hardiness Zone - 2012 | Zone 4a : -30°F to -25°F |
| Current Drought Conditions | Abnormally Dry |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |