Why Are My Tomato Leaves Turning Yellow? Common Problems & Fixes

A yellow tomato leaf isn’t cause for panic. But it is a sign that you need to take a closer look at your tomato plants. There are some simple reasons that leaves may turn yellow. From nutrient deficiencies to pests and diseases, you can learn to identify the cause and apply the right treatment.

When diagnosing the cause of yellow tomato leaves, first check whether older leaves are turning yellow or new leaves. This piece of information is important in diagnosing nutrient deficiencies.

A frost can damage the leaves and turn them yellow in the early spring and fall. If a newly transplanted tomato seedling has yellow leaves, it could be a sign of transplant shock. With proper care, the plant will recover. On an older tomato plant, yellow leaves can indicate the end of its life cycle.

Check tomato plants carefully for the presence of insects. Pests are often a cause of yellow tomato leaves. Many pests can be small and hard to see. A helpful method to identify pests is to hold a white sheet of paper up to the plant and shake the leaves.

Any pests will fall onto the paper, where you can see them more closely. A sticky trap can also catch roaming pests to help you see what’s munching in your garden.

These common issues are often the cause of yellow tomato leaves. Use this list to help identify and treat your plants.

Both too much and too little water can result in yellow tomato leaves.

When there is insufficient water, the leaves will droop and then turn yellow if the drought continues. Tomatoes need regular and deep watering. But don’t keep the soil too wet.

Overwatering can also result in yellow leaves. If the soil stays too wet, the roots will be prevented from taking up nutrients. Heavy clay soil will hold onto moisture and prevent oxygen from being available. If your soil has too much clay, amend it with compost.

Yellow tomato leaves can be a sign of plant disease. Each disease displays a unique pattern on the leaves, which can help determine what disease may be affecting your tomato plants.

When leaves turn yellow due to fungal diseases, you will also see small dark spots, usually with concentric rings. When fungal diseases are the culprit of yellow leaves, taking action quickly to save your tomato plants is crucial.

Powdery mildew starts out as white spots on the leaves, and as it progresses, it kills the plant tissue, and the leaves turn yellow. Powdery mildew is quite common in many climates, and there are helpful tips for prevention and treatment.

Verticillium and Fusarium wilt disease are both caused by pathogens in the soil. When tomato leaves turn yellow from wilt, you will first notice that even with consistent water, the plants droop. If these pathogens are present in your soil, consider planting yellow mustard as a cover crop. Yellow mustard has chemical properties that can help kill the wilt pathogens.

Tomatoes are considered “heavy feeders” and need a sufficient amount of nutrients to stay healthy. Nutrient deficiencies result in yellow leaves, stunted growth, and less fruit production. Getting the right nutrient mix will help your plants thrive.

Insufficient nitrogen is the most common issue for yellow leaves. When there’s not enough nitrogen, the older leaves turn yellow first. Following a healthy fertilizing schedule for tomato plants will help ensure the right amount of nitrogen at crucial growth times.

An iron deficiency is called iron chlorosis. One sign will be that the new leaves are turning yellow. The leaf veins will stay green, but the tissue between veins will turn yellow. Like many nutrient deficiencies, there may be plenty of iron in the soil; it just isn’t getting to the plant because of the soil pH. Tomatoes grow best in acidic soil. If the pH is too high, the plant can’t absorb iron. A soil test will determine if there is enough iron, and a pH test will help determine if you need to add amendments to change the pH.

Magnesium is required for chlorophyll formation, which gives leaves their green color. Similar to iron deficiency, magnesium deficiency in tomato plants results in green veins and yellow leaf tissue. The difference is that magnesium deficiency affects the older leaves first. The interveinal chlorosis pattern can look like spots at first. Magnesium deficiency is more common in sandy soil.

Yellow leaves can also be a sign of insect damage. Pests suck on the leaves feasting on the juices, and often spread disease. When pests attack tomato plants, they damage the plant cells, and the leaves can no longer photosynthesize. Identifying the specific pest can help you target your defense.

Aphid damage on tomato plants can be difficult to see until it is advanced. You may first notice sticky, shiny leaves. Aphids don’t often destroy a whole tomato plant but can affect the leaves. Encouraging beneficial predator insects is one natural way to get rid of aphids.

Damage caused by adult flea beetles leaves a scattering of various-shaped holes on the leaves. The damage is usually not fatal on mature plants, and the beetles can be controlled with natural methods. As with other insect damage, flea beetles can spread disease.

Thrips are hard to see, but their damage is easy to spot. As these minute insects suck out the green chlorophyll, the leaves will look yellow. Thrip damage to young seedlings is especially harmful. Waiting to plant out larger seedlings and using companion planting can help combat thrips in your garden.

Spider mites on tomato leaves will suck out the chlorophyll, lay eggs, and cover the plants in webbing. This can happen quickly since these insects have a rapid reproduction rate. Spraying tomato plants with water can wash off the spider mites and their eggs.

When yellow leaves appear, it is a sign that you should take a closer look at your tomato plants. Once you identify the reason for the change in color, you can remove the yellow tomato leaves and address the underlying cause. Yellow leaves are no longer benefiting the plant. If they are diseased, you will need to dispose of them in a garbage bag where they won’t infect other plants.

Take the necessary steps to address any nutrient deficiencies and eliminate pests and diseases. Gardening is a learning process every season. With a clearer understanding of what causes yellow leaves on tomato plants, you can save your tomato harvest.