The leaves on your tomato plants can turn yellow for several reasons. These culprits may range from fungus or insects to lack of proper nutrition. Yellow leaves are not only unsightly, but they are in danger of dropping from the plant early, exposing the tomatoes to too much sun. Working proactively to prevent these issues, as well as keeping an eye out for any signs of trouble, can help ensure yellow leaves never appear on your tomato plants.
Space your tomato plants at least 15 to 24 inches apart. Larger spaces between plants allow for better air circulation and make it harder for fungus to form.
Plant your tomatoes in a different spot than you did the previous year. Fungus can develop in the soil over the winter months. Wait at least two years before planting tomatoes in a location where they have been planted before.
Pick up any dead leaves or fruit that fall from the plant as soon as possible. Quick attention to fallen debris helps keep rot at bay.
Use row covers to shield your tomatoes from leafhoppers, insects that infect tomato plants with curly top virus. Curly top virus causes plants to turn yellow and then stops their growth.
Dust the leaves of your tomato plants with sulfur, which can be found at most garden supply stores. Apply according to the directions on the package. Sulfur helps prevent an infestation of some insects that feed on the plants and cause the leaves to turn yellow.
Plant tomatoes in a raised area. Leaves sometimes turn yellow as a result of poor drainage.