Johnston, South Carolina has a Humid Subtropical Climate climate (Köppen classification: Cfa). Average annual temperatures range from 50.8 °F (low) to 74.7 °F (high). Annual precipitation averages 46.7 Inches. Johnston is located in USDA Plant Hardiness Zone 8a. 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 | 33.2 °F | 55.5 °F | 4.19 in. |
| February | 34.8 °F | 59.1 °F | 3.69 in. |
| March | 40.9 °F | 66.6 °F | 4.42 in. |
| April | 49.2 °F | 75.2 °F | 3.18 in. |
| May | 58.1 °F | 83.0 °F | 3.18 in. |
| June | 65.6 °F | 89.3 °F | 4.62 in. |
| July | 69.2 °F | 92.3 °F | 4.25 in. |
| August | 68.0 °F | 90.8 °F | 4.75 in. |
| September | 62.8 °F | 84.9 °F | 3.9 in. |
| October | 50.6 °F | 76.1 °F | 3.02 in. |
| November | 41.1 °F | 65.6 °F | 3.35 in. |
| December | 35.9 °F | 57.6 °F | 4.16 in. |
| Annual | 50.8 °F | 74.7 °F | 46.71 in. |
| Average First Frost Date | Nov. 1 - Nov. 10 |
| Average Last Frost Date | Mar. 21 - Mar. 31 |
| Average Days With Frost | 50-75 Days |
| Plant Hardiness Zone | Zone 8a : 10°F to 15°F |
| Plant Hardiness Zone - 2012 | Zone 8a : 10°F to 15°F |
| Current Drought Conditions | Abnormally Dry |
| Köppen Climate Classification | Cfa - Humid Subtropical Climate |