Irmo, South Carolina has a Humid Subtropical Climate climate (Köppen classification: Cfa). Average annual temperatures range from 52.9 °F (low) to 74.8 °F (high). Annual precipitation averages 47.9 Inches. Irmo is located in USDA Plant Hardiness Zone 8b. The growing season typically runs from the last frost around Mar. 21 - Mar. 31 through the first frost around Nov. 1 - Nov. 10.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 34.6 °F | 56.0 °F | 4.0 in. |
| February | 36.8 °F | 59.5 °F | 3.73 in. |
| March | 43.2 °F | 67.1 °F | 4.24 in. |
| April | 51.4 °F | 75.6 °F | 3.04 in. |
| May | 60.4 °F | 82.7 °F | 3.27 in. |
| June | 68.3 °F | 88.8 °F | 4.82 in. |
| July | 71.4 °F | 92.0 °F | 4.22 in. |
| August | 70.7 °F | 90.4 °F | 4.92 in. |
| September | 65.0 °F | 85.4 °F | 4.25 in. |
| October | 53.3 °F | 75.9 °F | 3.79 in. |
| November | 42.4 °F | 65.9 °F | 3.53 in. |
| December | 36.8 °F | 58.3 °F | 4.1 in. |
| Annual | 52.9 °F | 74.8 °F | 47.91 in. |
| Average First Frost Date | Nov. 1 - Nov. 10 |
| Average Last Frost Date | Mar. 21 - Mar. 31 |
| Average Days With Frost | 40-50 Days |
| Plant Hardiness Zone | Zone 8b : 15°F to 20°F |
| Plant Hardiness Zone - 2012 | Zone 8a : 10°F to 15°F |
| Current Drought Conditions | Moderate Drought |
| Köppen Climate Classification | Cfa - Humid Subtropical Climate |