Yellow leaves on tomato plants can be worrying, but they do not always mean the plant is lost. The cause may be simple stress, watering trouble, lack of nutrients, or pests.
The best approach is to observe the whole plant before acting too quickly.
Both too much water and not enough water can turn tomato leaves yellow. Soil that stays soggy can suffocate roots, while very dry soil prevents the plant from absorbing nutrients properly.
Check the soil a few centimeters deep before watering again.
Older lower leaves often yellow when the plant lacks nitrogen. Other nutrient problems can cause yellowing between veins or pale new growth.
Feed tomatoes with a balanced fertilizer made for vegetables, but avoid overfeeding. Too much fertilizer can stress roots and reduce fruit quality.
Look under leaves for small insects, sticky residue, spots, or webbing. Yellowing with brown marks or wilting may point to disease or root problems.
In hot weather, lower leaves can also yellow naturally as the plant focuses energy on fruit and new growth.
Remove badly damaged lower leaves, improve airflow, water deeply but not constantly, and keep mulch around the base. Watch the plant for a few days before making big changes.
Tomato leaves turn yellow for several reasons, from watering problems to nutrients, pests, disease, or heat. Start with soil moisture and leaf inspection before choosing a fix.