Tomato Leaf Curl and Yellowing: Diagnosing Heat and Water Stress

Tomato in sandy, humus-rich soil at 30–35°C (86–95°F) with upward leaf curl and patchy yellowing? Classic heat and water stress. High temps reduce photosynthesis, curl leaves to reduce surface area. Sandy soil drains fast—roots may dry between waterings. Yellowing suggests nutrient uptake issues (calcium, magnesium) from irregular moisture.

Fixes: mulch 3+ inches (straw, shredded leaves) to stabilize soil moisture/temperature. Water deeply, consistently—drip irrigation ideal. Shade cloth (30–40%) during peak heat. Check for spider mites (underside of leaves). Foliar spray with kelp extract helps stress tolerance.

Resource: Colorado State's tomato problem guide (ext.colostate.edu/pubs/garden/02949.html) covers curl viruses, herbicide drift, and physiological disorders. Compare symptoms.

Tomatoes want 70–85°F days, consistent moisture. Adapt the environment, not the plant.