Why Are My Tomato Leaves Yellow?

As your tomato plant matures and puts energy into fruiting, it naturally sheds its lower leaves. If your plant is otherwise healthy, producing fruit, and only yellowing at the bottom — this is normal. Remove the yellow leaves to improve airflow and move on.

The most common nutritional cause of yellowing. Nitrogen deficiency starts with older, lower leaves going uniformly pale yellow, then progresses up the plant if not addressed. Often seen in container-grown tomatoes where nutrients run out quickly.

This causes yellowing between the leaf veins while the veins themselves stay green — called interveinal chlorosis. It's very common in tomatoes grown in pots or in acidic soils, and often gets worse as the season progresses and fruiting draws on the plant's reserves.

Overwatered tomatoes show yellowing that can appear anywhere on the plant. The soil stays constantly wet, roots lack oxygen, and nutrient uptake fails. Often confused with nutrient deficiency.

Brown spots with yellow halos on lower leaves, spreading upwards. A fungal disease that spreads quickly in warm, wet conditions — common in UK summers.

Dark, water-soaked patches on leaves that turn yellow and then brown rapidly, often with a white mould on the underside of leaves in humid conditions. Can kill a plant in days.