Why Are My Tomato Leaves Turning Yellow?

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Healthy tomato plants make fresh, delicious, sun-kissed tomato fruits. Unfortunately, tomato plants are susceptible to pests, diseases, and environmental issues; you may have encountered some during your time growing these highly sought-after fruits.

One such issue is yellowing tomato leaves. Various things can cause this problem. Luckily, you can easily fix and even avoid most of them.

In this guide, we’ll answer the question: Why Are My Tomato Leaves Turning Yellow? and explore practical solutions to restore tomatoes’ vigor and health.

Why Are My Tomato Leaves Turning Yellow?

 

1. Watering Issues

This is perhaps the most prevalent reason your tomato leaves are becoming yellow. The stress caused by improper humidity, underwatering, poor drainage, or overwatering can lead to yellow tomato leaves.

• Underwatering

Your tomato plants will prioritize where to direct their energy if they do not get enough water. First, the leaves will wilt and eventually become yellow. The color change will start with the margins turning golden and proceed until the entire leaf is yellow.

Solution

Water your tomato plant deep and consistently, ensuring your plants get about 1-1.5 inches of water per week. Increase the amount during hot spells.

• Overwatering

In your attempt to keep your tomato plants happy, you may end up suffocating their roots, causing rotting. Overly wet soils impede oxygen circulation and water and nutrient absorption. As a response, the leaves turn yellow.

Solution

 Wait for the topsoil to completely dry before watering your plants. If you are growing tomatoes in pots, provide enough drainage holes. In addition, re-pot waterlogged tomato plants in well-drained soil and avoid growing your tomatoes in areas susceptible to pooling.

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• The Best Companion Plants For Tomatoes
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2. Nutrient Deficiency

If you hope to harvest healthy tomatoes, ensure your plants get a balanced diet. Tomato plants need lots of nutrients, benefiting from doses of fertilizer regularly. They especially require a steady diet comprising potassium, phosphorus, and nitrogen to flourish.

They also need small amounts of micronutrients like iron, zinc, and magnesium. Nutrient deficiencies can result in yellowing leaves.

• Nitrogen: yellowing starts with the older leaves, while younger ones stay green. Severe cases of nitrogen deficiencies lead to leaf death.
• Potassium: the edges of the older leaves turn yellow and eventually brown, while the interior parts might stay green.
• Magnesium: older leaves gradually turn yellow; the veins stay green. The discoloration starts from the outside towards the inside.
• Iron: younger leaves turn yellow first; the older ones and the veins remain green. Unlike nitrogen deficiency, lack of iron affects the top leaves first.

Solution

Fertilize your tomato plants regularly for optimal fruit production and plant development. Feed these heavy feeders during planting and biweekly once they start setting fruit until they stop producing fruits.

Instead of guessing the nutrient deficiency affecting your plants, do a soil test. This way, you can target the issue correctly.

3. Transplant Shock

Have you noticed leaf yellowing in your newly transplanted tomato plants? You may have damaged the delicate roots while moving the plants or transplanted the seedlings too early.

Even the tiniest nick or breakage in your tomato plant’s root ball can cause root damage. Besides yellowing, you’ll notice the leaves wilting and curling.

Solution

Baby your plants for a while and give them time to recover. Also, do not exert other kinds of stress, such as poor watering and pruning, on them during recovery.

Avoid transplant shock altogether by gently transplanting your tomato plants—do not touch or cut the roots. If possible, shade your plants temporarily to ease their adjustment to the new place.

4. Temperature Stress

Tomatoes are sun-loving plants; they flourish in sunny, warm areas. The perfect temperatures for optimal growth, flower production, and fruit development are 70°F to 85°F during the day and not lower than 55°F at night.

Although tomatoes enjoy warm weather, they don’t handle extreme heat or cold. They stunt their growth, slow down fruit production, and even turn leaves yellow.

• Heat Stress

Extreme heat causes rapid transpiration, and if the leaves cannot absorb water fast enough to replenish the lost moisture, your plants will become dehydrated. The leaves may turn yellow. Prolonged exposure to intense sunlight causes leaf scorching (the edges turn yellow or brown).

Solution

Shield your tomato plants from extreme heat with shade and plenty of water. Also, increase humidity by misting the plants.

• Cold Stress

Low temperatures and the absence of sunlight slow down chlorophyll production and, in turn, photosynthesis, resulting in chlorosis— leaves lose their green pigment and turn yellow. This is usually caused by sudden temperature drops and cold drafts.

Solution

Bring potted tomato plants indoors or put them inside a cold frame during cold spells. Also, cover the plants with mulch, cloche, or fleece to help retain heat. You could also wait for the warm season to plant tomatoes outdoors.

5. Soil pH Imbalance

Your tomato plants will struggle with nutrient intake if the soil pH falls outside the optimal range—for tomatoes, this is between 6.0 and 6.8. Yellow leaves are early signs of pH imbalance. This yellowing resembles that of nutrient deficiency, but it persists despite fertilization.

Solution

Before making any adjustments, perform a soil pH test. Organic matter and sulfur lower the pH of alkaline soils, while wood ash, lime, and bone meal raise the pH of acidic soils. Also, avoid planting your tomatoes in the same area multiple times.

6. Soil Compaction

Oxygen cannot reach the roots of tomato plants if the soil is compacted, thus causing them to suffocate. This problem will first manifest itself with leaves turning yellow. If you don’t fix this issue, your plants will eventually wither and die.

What causes soil compaction? A few things make soils compact. These include stepping on it frequently or failing to aerate or loosen it.

Solution

Grow your tomatoes in good, well-draining soil enriched with organic matter, and loosen the soil before planting. Also, consider using containers or raised beds to avoid pets or people walking on the ground around your tomato plants.

Fix already compacted soil through aeration, but proceed cautiously to protect the roots.

7. Fertilizer Burn

Applying too much fertilizers to your tomato plants can be catastrophic as it causes salt buildup. Salts draw water away from the plant’s roots, dehydrating them.

Fertilizer burn causes the yellowing of tomato leaves, especially the lower ones. As the condition progresses, the leaf edges can turn brown or black. Fertilizer burn also causes wilting, leaf drop, and stunted growth.

Fertilizer burn is more prevalent in container-grown plants than ground-grown ones.

Solution

• Thoroughly flash your tomato plants with water. This works best in container-grown tomatoes.
• Test the soil before fertilizing your plants to avoid guessing the nutrients your garden needs. Moreover, use the recommended amounts, and if unsure, it’s better to use less.
• Water your tomato plants before and after fertilizing to dilute the fertilizer salts concentration.
• Consider using slow-release fertilizers or organic fertilizers because they gradually provide nutrients over time, reducing the risk of fertilizer burn.

8. Pests

Provided you continue growing plants, you just have to deal with pests. These tiny troublemakers are annoying, destructive, and often refuse to leave. A wide variety of pests attack tomato plants, and as they feed on the sap, roots, or foliage, they inadvertently cause damage that leads to stress and nutrient deficiencies.

Leaf yellowing that is localized around the infested parts is one of the signs of pest infestation. Common pests to look out for are aphids, hornworms, spider mites, thrips, whiteflies, cutworms, and flea beetles.

Solutions

Inspect your tomato plants regularly. Get rid of pests through handpicking, physical barriers, sticky traps, companion planting, beneficial insects, neem oil, or insecticidal soaps.

10. Diseases

Tomatoes are prone to various diseases that cause yellowing in leaves. Below are a few notable ones:

a) Early Blight

This common tomato disease is caused by the fungus Alternaria solani and affects the leaves, stem, and fruit. Early blight causes tiny black or brown spots on the lower leaves, which spread, grow large, and turn yellow.

Solution

• Remove the affected leaves.
• Apply a copper-based fungicide or organic fungicide the moment you detect the disease.

b) Late Blight

Unlike early blight, late blight can destroy an entire plant within a few days. Phytophthora infestans cause this disease. Its symptoms include major leaf yellowing and dark lesions on leaves and fruits.

Solution

• Remove the affected plants immediately.
• Apply preventative copper-based fungicides.

c) Fusarium Wilt

This disease starts in the soil, infecting the roots and thus preventing the movement of nutrients and water to the other plant parts. Fusarium Wilt causes yellowing, wilting, and poor growth and fruit production.

Solution

This disease has no cure, so destroy the affected plants immediately.

d) Verticillium Wilt

This disease is similar to Fusarium Wilt but less aggressive. It is more common in cooler temperatures.

Solution

• Remove the infected plants.

e) Tomato Mosaic Virus

Infected seeds usually transmit this highly contagious virus. Infected plants have yellow and mottled leaves with light and dark green mosaic patterns.

Solution

• Destroy infected plants.

Conclusion

Most causes of leaf yellowing in tomato plants are easy to fix, so this issue shouldn’t cause panic. Instead, uncover the causes and fix them. Keep in mind that perhaps your tomatoes are aging, and the older leaves are simply dying off.

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