Mertens, Texas has a Humid Subtropical Climate climate (Köppen classification: Cfa). Average annual temperatures range from 12.8 °C (low) to 25.2 °C (high). Annual precipitation averages 1003.3 Millimeters. Mertens is located in USDA Plant Hardiness Zone 8b. The growing season typically runs from the last frost around Mar. 1 - Mar. 10 through the first frost around Nov. 11 - Nov. 20.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 2 °C | 14.3 °C | 72.64 mm |
| February | 4.1 °C | 16.6 °C | 74.42 mm |
| March | 8.1 °C | 20.4 °C | 90.42 mm |
| April | 12.1 °C | 24.7 °C | 90.17 mm |
| May | 17.3 °C | 28.7 °C | 114.05 mm |
| June | 21.4 °C | 32.9 °C | 100.33 mm |
| July | 23.1 °C | 35.3 °C | 45.21 mm |
| August | 22.9 °C | 35.7 °C | 61.47 mm |
| September | 19.2 °C | 32.2 °C | 84.07 mm |
| October | 13.2 °C | 26.6 °C | 118.87 mm |
| November | 7.4 °C | 19.9 °C | 74.93 mm |
| December | 3.1 °C | 15.2 °C | 76.71 mm |
| Annual | 12.8 °C | 25.2 °C | 1003.29 mm |
| Average First Frost Date | Nov. 11 - Nov. 20 |
| Average Last Frost Date | Mar. 1 - Mar. 10 |
| Average Days With Frost | 30-40 Days |
| Plant Hardiness Zone | Zone 8b : -9.4°C to -6.7°C |
| Plant Hardiness Zone - 2012 | Zone 8a : -12.2°C to -9.4°C |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Cfa - Humid Subtropical Climate |