Why Are My Tomato Leaves Yellowing? Top Causes and Fixes

Tomato leaves yellowing is a sign of an underlying problem in your tomato plants. While there is no exact cause of yellow leaves in tomato plants, you need to find out whether the cause is watering issues or nutrient imbalance.

Don’t worry because yellow leaves are a common problem in tomato plants – the important thing is to correct the problem. When left unaddressed, the problem can affect the overall health and fruit production of your plants.

If you notice some yellow leaves on your tomato plants, here are some possible causes and how to fix them.

Why Tomato Plant Leaves Turn Yellow

Yellow leaves can be frustrating to any gardener. Luckily, most potential causes can be fixed to restore the health of your plants.

1. Watering Issues

Tomato plants just need the right amount of watering—too much or too little can cause tomato leaves to turn yellow. Too much water suffocates the roots, causing root rot and preventing them from absorbing nutrients, leading to yellow leaves. On the other hand, too little water causes the leaves to yellow, wilt, and dry out.

How to Fix This:

Don’t overwater or underwater your plants. Just give them the right amount that they need. Water only when the topsoil is completely dry, and avoid wetting the leaves.

2. Transplant Shock

If you notice yellow leaves after transplanting seedlings in the garden, your plants are going through transplant shock, which is completely normal. The sudden change of environment from indoors to outdoors might cause the plants to be stressed.

How to Fix This:

If you’re transplanting your plants, do so gradually to minimize the shock. After transplanting, give them the right care, like adequate water and protect them from cold temperatures. If it’s extremely cold (below 45 degrees F), cover them with cloth.

3. Nutrient Deficiency

One of the primary reasons for tomato leaves yellowing is the lack of essential nutrients. Tomatoes are heavy feeders, so they need plenty of nutrients to grow. Lack of nutrients in their growing season can cause the plant to develop yellow leaves.

The most common one is Nitrogen deficiency – which causes older leaves to turn yellow and finally fall off. Additionally, the plant can also have Iron deficiency (Iron Chlorosis) – which causes young leaves on healthy plants to turn yellow. Magnesium deficiency causes yellow spots in older leaves.

How to Fix This:

For nitrogen deficiency, use a balanced fertilizer or compost, while for iron and magnesium deficiencies, consider using Epsom salts or fertilizer with micronutrients like magnesium and iron.

4. Lack of Enough Sunlight

Tomato plants require 6-8 hours of direct sunlight daily to thrive and produce fruits. If they are not getting enough sun exposure, the leaves will start to turn yellow.

How to Fix This:

Plant your tomatoes in a location where they will receive ample sunlight. If there are plants in your garden shading your tomatoes, you might consider getting rid of them. For tomatoes in containers and pots, position them in a spot where they will receive enough sunlight.

5. Fungal and Bacterial Diseases

Tomato leaves yellowing might be a sign of fungal or bacterial diseases. Below are common fungal and bacterial diseases.

Common Fungal Diseases:

Early Blight – Early blight starts as small brown spots on lower older leaves, which later develop yellow edges.

Fusarium Wilt (Fusarium oxysporum) – This fungal disease causes yellowing and wilting of lower leaves, which gradually spread to upper leaves. The leaves may later turn brown and die.

Septoria Leaf Spot (Septoria lycopersici) – The first signs are small, water-soaked spots with dark borders that appear on lower leaves and then turn yellow.
Verticillium Wilt—Similar to fusarium wilt, this disease causes yellowing of the lower leaves, which may develop V-shaped lesions and curl upwards.

How to Fix This:

Remove the affected leaves and dispose of them properly, and practice crop rotation to avoid planting tomatoes in one spot for years. You can also apply fungicides like copper sprays or those containing chlorothalonil.

Common Bacterial Diseases:

Bacterial Spot – Bacterial spot causes small, water-soaked lesions on the leaves, which turn yellow and then brown

Bacterial Speck – This bacterial disease appears as small dark lesions on the leaves surrounded by yellow halos. The affected leaves later turn yellow.
Bacterial Wilt—The disease causes the sudden yellowing and wilting of younger leaves on one side of the plant. The plant eventually dies.

How to Fix This:

To prevent bacterial diseases in your tomato plants, grow those varieties that are resistant to bacterial diseases. Remove and destroy the infected leaves and practice crop rotation. You can also apply copper-based bactericides.

6. Herbicide Damage

Tomato plants are susceptible to herbicides, and exposure to them might cause yellow leaves, curling leaves and even stunted growth. Even herbicide applications from your neighbour’s farm can drift by winds to your tomatoes.

How to Fix This:

There is no known remedy for tomato plants exposed to herbicides. The best thing to do is to avoid using herbicides near your tomatoes.

7. Pests

Pests such as aphids, spider mites, whiteflies, and flea beetles can suck sap from your tomato leaves, causing them to turn yellow.

How to Fix This:

Apply horticultural oils or insecticidal soap to get rid of the small pests. You can also consider planting bug-repelling herbs like mint near your tomatoes to act as natural pest repellents.

Final Takeaway

Don’t panic—tomato leaves yellowing is a common issue. The most important thing is to identify the issue and correct it immediately.

If you want healthy plants, understand their needs and respond quickly to any signs of distress. To save your tomatoes from developing yellow leaves, ensure they get enough sunlight and nutrients and protect them from herbicides and pests.

Author Profile

Mary

🌿 Hello! I'm Mary, the nature-loving soul behind Serene Eden. Gardener, plant whisperer, compost connoisseur, sun-soaked plant enthusiast, and avid bee-watcher. Let's cultivate beauty, one bloom at a time. 🌱🌼