Tomato plants turn yellow for a variety of common reasons, including:
- Improper watering: Both overwatering and underwatering can cause yellow leaves. Tomato plants need deep, regular watering but the soil should dry out between watering to avoid sogginess and root rot. Watering at the base and early in the day is best.
- Nutrient deficiencies: Lack of nitrogen is a frequent cause of yellowing, especially on older leaves, as the plant moves nitrogen to younger leaves. Deficiencies in magnesium or iron can also cause yellow leaves or yellow spotting.
- Sunlight deficiency: Tomato plants need at least 6 hours of direct sunlight to thrive. Lack of sufficient sunlight can cause lower leaves to yellow.
- Transplant shock: When young tomato plants are moved outdoors, some temporary yellowing may occur as they adjust.
- Diseases: Several fungal and bacterial diseases cause yellowing leaves with distinctive patterns or spots, such as early blight, late blight, Fusarium wilt, and Septoria leaf spot.
In summary, yellow tomato leaves are often due to watering issues, nutrient deficiencies, sun exposure, transplant stress, or diseases. Identifying the specific cause involves checking watering practices, sunlight, signs of disease, and soil fertility to apply the correct remedy for healthy tomato plants.