6 Reasons Your Tomato Leaves Are Turning Yellow & How To Fix Them

6 Reasons Tomato Leaves Turn Yellow
Tomato Leaves Turning Yellow

Tomatoes are a popular garden vegetable because they are relatively easy to grow and they are versatile in the kitchen. But sometimes tomato plants can experience problems, like leaves that turn yellow.

There are several reasons why this might happen, and fortunately, there are steps you can take to correct the problem. In this post,

We will explore 6 Reasons Tomato Plants Turn Yellow and suggest solutions on how to fix this issue.

1. The Seed Leaves Are Turning Yellow on Tomato Plants

Okay, let’s just cover this one first as it’s one of the most common worries for new tomato growers and shouldn’t be a worry at all.

If your young tomato or seedling plants’ leaves are yellowing, do not stress over it. These are the seed leaves (also called cotyledons). They’re among the first leaves to sprout after seeds sprout but are not considered “true” leaves.

It is in the early stage of growth that these leaves transform from green to yellow and brown stems and finally drop off. It is important to not worry too much about these leaves.

2. Soil Compaction

The Cause

The roots of tomatoes need air and water just like any other plant. If the soil in which they grow is aerated enough, however, then they will thrive and continue to produce.

As springtime comes into full swing, plants begin to show their vibrant colors. They come to life and prepare for reproduction. That’s what causes them to turn bright yellow.

A similar problem occurs when the soil around your tomato plants has insufficient aeration. The roots do not have access to enough oxygen, and they start to suffocate. The roots can’t transport fluids, air, and nutrients throughout the plant.

This causes the tomato leaves to turn yellow and is a sign that the plant is dying.

You can begin to aerate the soil by loosening it with your hands. This is often recommended by experts, but it can damage the root system. The better alternative is to start the seed in enriched soil to avoid any problems from the start.

3. Watering Problems

The Cause

The most likely cause of leaf yellowing in tomatoes is inadequate water supply. Too much watering leads to roots becoming waterlogged, and if that happens, the plant will need to dry out completely before resuming normal growth.

When it comes to keeping plants alive, we often err in the other direction. We’re afraid that if we don’t give plants enough water, their roots won’t have enough oxygen, so we’ll flood the soil.

The soil’s excess water can damage the roots, suffocate the roots and cause them to rot. If the roots are damaged and there’s less oxygen in the soil, there will be less oxygen available to the leaves.

The Solution

You can typically determine if it is an issue of overwatering or underwatered by assessing how well your plants are doing and the state of the soil. Overwatering will cause your plant’s roots to rot and the plant’s growth will be stunted, whereas underwatered plants may appear to be fine but could actually be suffering from root rot.

Correct watering is vital to the health of your tomato plants. Check the soil regularly and only water when the plant is absolutely thirsty – about when the top 1 or 2 inches of soil has dried out.

Water should be applied to the soil around the roots, not the leaves, and slowly, deep down. If you do it right, you’ll find the soil has already absorbed the moisture and you won’t have to water the plant.1.

If you find that overwatering is causing your plant’s problem and the problem is not remedied, you may be dealing with a bad case of root rot. Unfortunately, it’s very difficult to treat plants in this situation.

Although the roots may be damaged, they’re still alive. And since you’ve planted them in a safe and healthy location, you don’t want to kill them off yet. Wait for the shoots to grow before you remove the roots.

4. Transplant Shock

The Cause

If you’ve recently transplanted your seedlings and noticed yellowing leaves on the bottom of the plant, transplant shock is likely the cause. Transplant shock happens when seedlings are moved from a warm spot, such as a greenhouse or indoors, to cold soil outdoors.

The shock can cause the bottom few leaves of the plant to turn yellow. Fortunately, this is only a short phase of adjustment. While it’s true that the yellow leaves will eventually fall off and the plant will return to its normal appearance, there is nothing to worry about – and this is just a short phase of adjustment.

As transplant shock is not normally a fatal issue for your tomato plants, however preventing it is the best option. If you have a cold winter, you can warm the soil before transplanting. Don’t wait for nighttime temperatures to drop below 50 degrees Fahrenheit.

In order to keep your plants healthy, it’s important to remove any leaves that aren’t growing.

5. Diseases

The Cause

Tomato plant disease is the most common one that causes yellowing leaves in tomatoes. Many of these diseases can be difficult to combat once they become established in the crop.

One of the major root causes of the beginning of early blight is actually a fungus that lives in the soil. It’s fairly simple to spot, as there is a thin yellow patch on the underside of the leaves. If left unchecked, the leaf will start to turn yellow and eventually decay.

Tomato plants with leaf spots caused by another fungus, Septoria leaf spot, will often appear to have similar markings to other common tomato diseases. The difference is that this one causes the leaves to curl and wither, and in the worst cases can cause plants to die.

There are also different forms of wilts caused by different viruses or fungal pathogens.

The three main forms of wilt are Fusarium wilt, Verticillium wilt, and Bacterial wilt.

Fusarium wilt is a common fungal disease that starts in the soil and infects the roots of the plant. The plant will look like it is dead even if it has sufficient water, and the leaves will fall from the bottom of the plant up.

Verticillium wilt symptoms resemble those induced by early blight and septoria leaf spot, and you will notice pale-colored spots on the lower leaves. 

Less frequently seen is Bacterial wilt, caused by bacteria often found specifically in sandy soils when they are wet. and often develops after a crop is transplanted, although there is no proof of the disease until several years later. The leaves wilt and begin to look yellow early in the growing season.

Any symptoms of infection in your tomato plants require immediate treatment. If left untreated, the issue can spread to the rest of your plant, and other parts of your garden.

Blight and Septoria leaf spot can be treated if detected early. Remove these leaves and discard them, keeping them separate from other green plants in your garden. Apply a fungicide specifically designed to treat the issue, following the instructions on the product exactly until the problem is resolved.

6. Nutrient Deficiency

The Cause

Nutrient deficiencies can occur because there is not enough of a nutrient in the soil for your plants to consume. These problems are often caused by poor soil fertility, which can lead to nutrient deficiencies.

The main culprit in yellowing leaves is nitrogen. This nutrient is essential to healthy growth and leaf production. Inadequate nitrogen limits the ability of leaves to synthesize chlorophyll and cause a loss in the amount of green in the leaves.

If a plant’s foliage starts to turn a shade of yellow, there’s a good chance you need to fertilize it with nitrogen. The same goes for your business – if you want your product or service to grow, you need to keep providing your customers with what they need.

A lack of certain micronutrients can also cause the leaves to yellow. When the tomato plant lacks access to certain micronutrients (which are required for proper photosynthesis), it cannot produce enough chlorophyll.

This causes the leaves to turn yellow, while the veins remain bright green.

If you’re seeing nutrient deficiency in your plants, check your fertilizer. All-purpose fertilizers will contain some of each nutrient in a balanced ratio to offset any deficiency in the soil.

To be sure of the problem, Soil tests are one way of confirming the origin of a problem and letting you know what specifically is causing the issue.

If a soil test is needed, a magnesium deficiency can be addressed by planting Epsom salt on the leaves. You will not know if a deficiency is present until conducting a soil test. Attempting to fix the issue with a solution may not be necessary, as it could worsen the condition.

A soil test may also reveal whether the plant is the source of the nutrient deficiency or if there’s a problem with the soil.

Remember, a nutrient deficiency can occur in a plant even when there isn’t a problem with the soil. It may be caused by the lack of nutrients in the plant’s roots that are impaired from transporting them through the plant rather than an issue with the soil.

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