There are a number of causes for tomato leaves turning yellow. Most of the time this is not really a problem and won’t affect your fruit. I have 2 tomato plants in pots side by side in my garden. One of the plants has yellowing leaves and the other one doesn’t.
In addition, I have numerous other tomato plants scattered around the garden and in pots and none of those seem to be affected with yellowing leaves.
My 2 tomato plants side by side
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Fruit on the plant with yellowing leaves
So, I decided to do some investigation and here’s what I found.
Fungal Diseases Can Cause Yellowing Leaves
There are at least 3 fungal diseases that can affect tomato plants and cause the leaves to turn yellow.
Early Blight
Late Blight
Fusarium Wilt
- Early Blight. This shows up as yellow leaves. The leaves have small spots that grow larger. They end up taking on a bulls-eye appearance. Thankfully, this generally doesn’t affect the fruit.
- Late Blight. This starts on the upper leaves. It causes large lesions on both leaves and stems. These generally look oily.
- Fusarium Wilt. This disease is common in warm weather. It causes yellow leaves on one side of the plant and starts with the bottom leaves. The disease stunts the growth of the plant and no fruit production is likely.
To control fungal diseases, you’ll need to spray them with a fungicide that contains chlorothalonil. It’s also really important to water the soil the plant is growing in and not the leaves. It also helps to increase air circulation by removing excess leaf growth.
You should also remove the infected leaves if you can. This means that the fungal infection won’t spread to the rest of the plant.
It’s also a good idea to cut off the lower leaves from your tomato plants. Especially if they’re touching the ground. This encourages airflow and stops any diseases from splashing up onto the leaves.
Viral Diseases Can Cause Yellowing Leaves
There are a variety of viral diseases that can cause yellowing leaves. These include:
- Tomato Mosaic Virus
- Tomato Yellow Leaf Curl
- Tobacco Mosaic Virus
- Cucumber Mosaic Virus
- Single Streak Virus
Most of these viruses cause stunted growth and a mosaic type pattern on the leaves. These viruses can also cause malformations like severe curling of the leaves.
Much like human viruses, plant viral infections cannot be eliminated. If you have a plant that’s heavily infected, it’s best to discard it completely. Thankfully, there are a lot of disease-resistant varieties of tomato plants readily available now.
Certain Pests Can Be The Cause Of Tomato Leaves Turning Yellow
Common pests that you can find attacking your tomato plants are:
- Aphids
- Thrips
- Spider Mites
- Flea Beetles
- Whiteflies
- Hornworms
- Cutworms
If you feel that you might have this problem, then you can spray your plants with insecticidal soap or a horticultural oil such as white oil.
Incorrect Watering Can Also Turn Tomato Leaves Yellow
Either too much or not enough water can turn your tomato leaves yellow. Tomatoes are quite thirsty plants and they really don’t like drying out too much. Depending on the weather, you should thoroughly soak the soil every 5 – 7 days.
On the other hand, it’s not good for the soil to be soggy either. This means careful monitoring of your plants to ensure they’re getting just the right amount of water that they need.
If you can manage it, drip watering is ideal for tomato plants. This method gets the water to the roots of the plants where it’s needed. It also eliminates the risk of the leaves getting wet.
Remember too, that plants growing in pots tend to dry out much faster than those growing in the ground. I suspect that this may be the problem with my tomato plants as these pots receive quite a lot of sunlight during the day. Plus, the green one did display some signs of wilting when we had a few days of warmer weather.
Getting Enough Nutrients Is Important For Your Tomato Plants
Plants that have the bottom leaves turning yellow are generally nothing to worry about. It might just mean that these leaves are not getting the nutrients they need. Or, they may not be getting enough sunlight if there’s a lot of growth on top.
Tomatoes are heavy feeders. This means that they require a fair amount of nutrients to grow and thrive. For tomatoes, it’s important to give them both nitrogen and potassium.
The nitrogen keeps the plant growing and the leaves green. Potassium, on the other hand, promotes good fruit growth.
So, if your tomato leaves are turning yellow, it may mean you should give them a good dose of nitrogen. Remember to balance that with potassium as well. Otherwise, you’ll get plenty of lush green growth but no fruit.
Tip: Add banana peels or coffee grounds to the soil to increase the level of potassium. You can also purchase fertilizers that are specifically made for fruiting plants.
Frequently Asked Questions
Ensure that your plants are receiving enough water and the nutrients that they need. Apply a general-purpose fertiliser that contains both potassium and magnesium to keep your plants healthy.
Yes, if your tomatoes are growing in soil that does not drain adequately, the roots of the plants may not be getting enough oxygen and this can cause the leaves to turn yellow.
The lack of major nutrients such as nitrogen, potassium and also magnesium can cause your tomato leaves to turn yellow.
Final Thoughts
The best way to determine why your tomato leaves are turning yellow is to use the process of elimination. Look at all the possible causes and eliminate the ones that don’t seem probable.
Then you can work on correcting the problem if you have to.
For my particular plant, I did see some whiteflies around it so this may also be the culprit. As long as these don’t attack the fruit, I’m not too concerned about them though.
For the time being, because the plant is fruiting nicely, I’m just going to remove the yellow leaves and give the plant some additional nitrogen. I have plenty of other tomato plants in the garden so if I do end up losing this one, it’s not the end of the world.
Do you have problems with your tomato plants? Are there solutions that have worked well for you? Please feel free to share your experiences with us in the comments below.
