What causes tomato leaves to curl or turn yellow?
Written by
Liu Xiaohui
Reviewed by
Prof. Martin Thorne, Ph.D.Tomato leaf curling or yellowing is often a sign of underlying issues, e.g., heat stress. Tomato leaves can cup upward as temperatures rise during a heat wave. Yellowing patterns usually indicate a specific nutrient deficiency. Both of these problems occur as a result of environmental stress, pest damage, or mistakes in care. Determining the exact cause will help you tailor the remedy to the problem.
Water-Related Stress
- Overwatering causes yellow lower leaves and root suffocation
- Underwatering makes leaves curl inward to conserve moisture
- Inconsistent watering leads to yellowing between veins
Nutrient Shortages
- Nitrogen deficiency: overall yellowing starting from bottom
- Magnesium lack: yellow between veins on mature leaves
- Potassium shortage: brown leaf edges with curling
Heat stress, when temperatures climb above 90°F, causes dramatic curling upward. This also reduces leaf surface area to conserve water. If you get a heatwave, ensure they get afternoon shade. Mulch will help to keep your roots cool. Water deeply before the worst heat hits. Mine came back within days once I provided them with shade.
Nutrient problems vary considerably. For example, the lack of nitrogen will first cause the older leaves to yellow. The lack of magnesium will cause a mosaic pattern. The lack of potassium will cause the leaf edges to brown. Test the soil before applying any supplements. Balanced fertilizers can correct most deficiencies relatively quickly.
Viral illnesses can cause downward curling of the growth, also known as 'stunting'. Aphids dispense these viruses, which cannot be cured. If you do spot an infected plant, remove it immediately. You can control aphids by spraying them with neem oil. Plant resistant varieties such as 'Defiant' or 'Mountain Merit' to help protect your tomato plants.
Too much water causes leaves to be yellow and limp. Check your soil moisture before watering. If you dig down 3 inches and the soil feels moist, wait to water. If you have heavy soils, you may need to improve the drainage. Underwatered plants have crispy and curled leaves. Water them until the water drains out of the bottom of the container.
Read the full article: 8 Common Problems With Tomato Plants and Solutions
