Growing tomatoes is the go-to vegetable when starting a container garden. Though it’s beginner-friendly, growing tomatoes do come with its challenges. 

It is no wonder why many gardeners panic when they see yellow leaves on their tomato plants. Is the plant dying? Am I doing something wrong? All these questions and no answers! 

Tomatoes are known to be heavy feeders which means they have higher nutrient needs than other plants so more attention is needed. With that being said, yellowing leaves on tomato plants are a common problem and there could be various reasons for this. 

This could be a sign of nutrient deficiencies,  pests, diseases, environmental stress to even incorrect watering.  

Identifying the underlying cause of yellow leaves is crucial to ensure the plant’s health and productivity. When left untreated, yellow leaves can affect the plant’s ability to photosynthesize and produce fruits. And we don’t want that! We want to see the fruit of our labor.

The Common Causes of Yellow Leaves on Tomato Plants

yellow leaves on tomato plants

1. Lack of Nutrients 

The common nutrient deficiencies that cause yellow leaves on your plant include nitrogen, magnesium, and iron.

Nitrogen deficiency can be identified by the yellowing of the lower leaves, which progresses toward the upper leaves. The leaves may also appear stunted and the growth of the plant may be slow.

To identify magnesium deficiency, look for yellowing of the leaves, especially between the veins, while the veins themselves remain green. This may look more like speckles or spots of yellowing.  This is often referred to as “interveinal chlorosis.”

And lastly, iron deficiency is most common with new growth or the youngest leaves turning yellow with green veins.

How to fix it?

If your tomato plant is experiencing a nutrient deficiency, there are a few steps you can take to rectify the situation. First, identify the specific nutrient that is lacking by observing the symptoms of the plant listed above.

Once you have identified the nutrient, choose an appropriate fertilizer that contains the required element.

Apply the fertilizer according to the manufacturer’s instructions, ensuring that you do not over-fertilize as this can cause further damage to the plant.

Additionally, ensure that the plant is receiving enough water and sunlight, as these are essential for proper nutrient uptake. With proper care and attention, your tomato plant should recover from nutrient deficiency and thrive.

2. Fungal Diseases 

Fungal diseases are a common cause of yellowing leaves on tomato plants. One such disease is early blight, caused by the fungus Alternaria solani. This disease usually starts with yellow spots on older leaves that eventually turn brown and die.

Another fungal disease that causes yellowing leaves on tomatoes is Septoria leaf spot, caused by the fungus Septoria lycopersici. This disease usually appears as small, circular spots with a dark border and a yellow center. As the disease progresses, the leaves turn yellow and eventually fall off.

How To Fix It? 

Fungal diseases can cause a lot of damage to tomato plants, but there are steps that can be taken to control and prevent them.

The first step is to remove any infected plant material and dispose of it properly to avoid spreading the disease. It is also important to avoid overwatering and to provide good air circulation around the plants.

Applying a fungicide can also be effective in controlling the spread of the disease. You can use fungicide regularly whether you think you need it or not.

Preventative measures such as using disease-resistant varieties and rotating crops can also help to reduce the likelihood of fungal diseases affecting your tomato plants. Regular monitoring and prompt action will ensure that your tomato plants remain healthy and productive.

3. Improper Watering

Improper watering can cause the yellowing of tomato leaves because it can lead to either overwatering or underwatering.

Overwatering can cause the roots to suffocate and rot, leading to a lack of oxygen and nutrient uptake by the plant, resulting in yellowing of leaves.

Underwatering can cause the plant to become stressed and unable to absorb necessary nutrients, leading to the yellowing of leaves as well. Both scenarios can also lead to the development of fungal diseases that cause yellowing of leaves.

Thus, it is crucial to maintain proper watering practices to ensure the healthy growth and development of tomato plants.

How to fix it?

Here are a few tips on how to ensure you water your tomato plant properly: 

  • Water your tomato plants deeply and regularly to promote healthy root growth.
  • Use a soaker hose or drip irrigation system to water deeply and evenly.
  • Water your tomato plants at the soil level and avoid getting water on the leaves, as this can promote disease.
  • Water your tomato plants in the morning or early afternoon to prevent excess moisture on foliage overnight, which can lead to fungal problems.
  • Adjust watering schedule based on weather conditions – during hot, dry weather, plants may need more frequent watering, while during cool, rainy weather they may require less.
  • Monitor soil moisture by sticking your finger an inch deep into the soil. Water when the top inch of soil feels dry.

4. Pest Problems 

Some pest problems that cause tomato leaves to turn yellow include whiteflies, spider mites, aphids, and thrips. These pests suck the sap from the leaves and cause them to turn yellow and eventually die.

Additionally, tomato plants may be affected by diseases like bacterial spots or fusarium wilt that can also cause yellowing of the leaves.

How to Fix It?

To control pests that cause yellowing of tomato leaves, it is important to monitor the plants regularly for signs of infestation.

If you detect any pests, it is best to treat them immediately with an appropriate pesticide or insecticide.

In many cases, controlling the spread of disease can also help to prevent pest problems. For example, regularly removing infected leaves and avoiding overwatering can help keep your tomato plants healthy and reduce the chances of a pest infestation.

5. Lack of Sunlight

Lack of sunlight can cause yellow leaves on tomato plants because sunlight is essential for the process of photosynthesis. Photosynthesis is the process by which plants convert sunlight into energy to produce food.

Without enough sunlight, the plant cannot produce enough energy to sustain the leaves, which then turn yellow and eventually die.

Additionally, sunlight helps the plant to produce chlorophyll, the green pigment responsible for the color of leaves. Without enough sunlight, chlorophyll production decreases, leading to yellowing of the leaves.

How to fix it?

To ensure your tomato plants get enough sunlight, make sure to place them in a sunny location where they can receive at least 8 hours of direct sunlight each day.

Additionally, you can increase light exposure by pruning away any branches that are blocking the sunlight and using reflective material such as white rocks or foil to help increase the amount of light reaching the plant.

Lastly, avoid overcrowding your plants; if there is not enough air circulation between them, it can reduce their access to sunlight and cause yellow leaves.

6. Transplant Shock

Transplant shock can cause yellow leaves on tomato plants because it disrupts the plant’s ability to absorb water and nutrients, leading to stress.

When a tomato plant is transplanted, it experiences a period of adjustment where it must establish new roots in the soil. During this time, the plant may struggle to take up enough water and nutrients, causing its leaves to turn yellow.

Final thoughts on what to do when you see your tomato leaves turning yellow

In conclusion, there are several reasons why tomato leaves may turn yellow, such as overwatering, pest problems, lack of sunlight, and transplant shock.

It is important to identify the cause of the yellow leaves in order to find an appropriate solution. If the problem is caused by overwatering, adjust your watering schedule and monitor soil moisture. If pests are causing the yellowing leaves, it is important to treat them immediately with pesticides and the list goes on. 

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