Castroville, California has a Warm-Summer Mediterranean Climate climate (Köppen classification: Csb). Average annual temperatures range from 48 °F (low) to 62.8 °F (high). Annual precipitation averages 16.5 Inches. Castroville is located in USDA Plant Hardiness Zone 9b.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 42.5 °F | 60.3 °F | 3.31 in. |
| February | 43.4 °F | 60.7 °F | 3.31 in. |
| March | 44.5 °F | 61.7 °F | 2.23 in. |
| April | 45.6 °F | 60.9 °F | 1.31 in. |
| May | 49.0 °F | 61.4 °F | 0.45 in. |
| June | 51.5 °F | 63.4 °F | 0.13 in. |
| July | 54.3 °F | 63.7 °F | 0.05 in. |
| August | 54.7 °F | 64.6 °F | 0.05 in. |
| September | 53.2 °F | 65.8 °F | 0.09 in. |
| October | 49.5 °F | 66.5 °F | 0.7 in. |
| November | 45.2 °F | 64.3 °F | 1.65 in. |
| December | 42.1 °F | 60.1 °F | 3.21 in. |
| Annual | 48 °F | 62.8 °F | 16.49 in. |
| Average First Frost Date | No Frost |
| Average Last Frost Date | |
| Average Days With Frost | Frost Free |
| Plant Hardiness Zone | Zone 9b : 25°F to 20°F |
| Plant Hardiness Zone - 2012 | Zone 9b : 25°F to 20°F |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Csb - Warm-Summer Mediterranean Climate |