Why Are Tomato Leaves Turning Yellow?

Tomatoes are just like other plants. If you take care of them, they will give you lots of fruits as a “thank you”. Like other plants, tomato plants need detailed attention, because if something is missing, they can get weak and unhealthy, then they could die.

yellow tomato leaves

But how do you know if you’re doing it right or wrong? Trust me, the tomato plant will let you know. One of the signs if something is not right, is that their leaves are turning yellow.

There are a number of problems that can lead to yellow leaves, however, one or two of them on your tomato plants is often nothing to worry about.

In this article, I am going to talk about a few factors which can cause yellow leaves on your tomato plant.

Yellow Tomato Leaves – Causes & Treatments

As I mentioned earlier, several things can lead to yellow leaves on tomato plants, sometimes it can be something simple, such as too much watering. Sometimes yellow leaves can indicate a serious problem such as disease or pest attack. Simple problem or a serious one, if there is no action to resolve it, your plant could die.

So here you can find a few of the causes and solutions for your problems:

Watering Problem

Too much water or not enough water could both lead to yellowing leaves. You can easily manage this problem, as you can control how much water you use to water your plants.

You should take into consideration the weather you have and the type of soil, also, the level of mulch you are using. In some cases, you might need to water the plants multiple times a day. But in some cases, once a day or only a few times a week is enough.

Before watering your plants, you should always check the soil first. It shouldn’t be wet and soggy, but also not too dry.

You should also be careful about how you water your tomato plants. Always water in the early morning, if that is possible and make sure, you don’t sprinkle water on the leaves of the plant.

Transplant Shock

Transplant shock can also cause yellow leaves on tomato plants. If you transplant your plants in the early spring and nights are not warm enough yet, the plants will have one or two weeks of transplant adjustment period. In this period the older leaves may become lighter in colour or even yellow, but the new leaves should be healthy and green.

If the tomato plants’ lower leaves are yellow, you can cut them off, because that could be only a place for disease.

Transplant shock can be prevented by waiting for the ideal time to transplant your tomato plants. Let the temperature grow, especially during the night should be at least 10°C/ 50°F. This will help the plant to adapt easier to its new environment and the leaves will not become yellow.

Nutritional Deficiencies

Nutritional Deficiencies occurs when your soil is poor in magnesium, potassium, nitrogen and calcium, because is infertile, exhausted, or the soil’s pH is alkaline.

If tomato plants or any other heavy feeders are planted several times in the same place, this leads to nutritional deficiencies. If there is not enough nutrition, your tomato plants will not thrive and their leaves will become yellow, discoloured or even brown.

To prevent nutritional deficiencies in the soil if you have the possibility, change your tomato plants’ planting space yearly, but if your garden is small or you are planting in growing bags or beds, as I am doing, you should change the soil completely.

Even regular fertilizing would be a saving action for your plants. But if you notice nutritional deficiencies, doesn’t mean that you have to over-fertilize. That could harm your tomato plants.

Nutritional deficiencies can be caused by underwatering your plants. If there is not enough water, the roots cannot absorb the needed nutrients from the soil.

But how do you know which nutrient is lacking? There are some differences between the yellow leaves from which you can “read” the signs.

Lack of Nitrogen

The older leaves will turn yellow, whereas the top of the plant and the new leaves will remain green, also its growth will slow down. When Nitrogen is lacking in the soil, you can add urea or ammonium to it, but only in moderation.

Lack of Potassium

If your tomato plants’ leaves become limp and between the veins turns kind of a yellow, it is a lack of Potassium. This is the sign when you could add potash to the soil.

Calcium Deficiency

It will not lead to whole yellow leaves on the bottom of the plants, but on the top of it (blossom end rot). Adding some fertilizer that contains calcium, can save the problem.

Deficit of Magnesium

Can also cause the stunt of the growth in the plant. The leaves will have a golden border, or there will be some yellow spots on the leave which can grow bigger if the problem persists. Usually, the veins of the leaves will remain green, but the rest of it will turn all yellow. If you add some Epsom salt to the soil, this problem can be easily solved.

Sulphur and Zinc Deficiency

Will lead to yellow leaves on the top of the plant, while the older leaves will stay green. Just add some Sulphur and Zinc to the soil, and it is already sorted.

Please, remember, those leaves which turned yellow, will stay yellow. There is nothing to do to turn them back green. If fertilizing your plants will not stop the spreading of yellow leaves, it means, the problem is not a nutritional deficiency.


If your plants are not lacking in nutrition, you are watering them right, but the leaves are still turning yellow, the problem can be a disease. If it is so, the whole plant should be affected. So, for example, when nitrogen is lacking, the bottom leaves are affected. However, when it is a disease, there could be yellow, or sick leaves all over the plant.

There can be fungal diseases or viral diseases.

Fungal Disease

Some of the fungal disease, such as early blight, late blight and fusarium wilt can cause a lot of trouble, but you can treat it, whereas the viral disease, unfortunately, cannot be treated.

Early blight will not affect the fruits if it is not severe and, in its case, you can observe yellow leaves and small lesion spots. These can grow and spread.

Late blight is a more serious infection. You can recognise it by the oily-looking lesions on the leaves and stems as well.

Fusarium wilt affects the plant during warm weather and usually, the yellow leaves will appear on the bottom and only on one side of the plant. This can spread to the upper leaves; the growth of the plant will slow down or eventually stop.  Fusarium wilt is a disease that can stop the plant to produce fruits.

Luckily, you can treat fungal diseases by removing the sick leaves and destroying them. You should treat the plant with a fungicide containing chlorothalonil. Also, if you are watering properly and between the plants, there is enough space, so the air can circulate between them, which can help a lot.

Viral Disease

Viral diseases, such as tobacco mosaic virus, single steak virus, mosaic virus, and cucumber mosaic virus can be recognised by the mosaic pattern on the leaves but also will be a cause of the plants’ growth stunt. Pests, like whitefly or aphids, but also dirty or infected tools or hands can spread diseases.

Unfortunately, viral diseases cannot be treated, there is no chemical treatment. Therefore, you should destroy your sick plants, and replant new ones, preferably disease-resistant tomato plants. Make sure, that you plant the new tomatoes on another spot of the garden, not on the same place where the sick plats were before.


As I mentioned above, pests can be a cause of yellow leaves on tomato plants. Pest infection is not always obvious, but you can check by turning over the leaves and checking the stems so you can see the little trouble makers.

You can use insecticides or if you want to go natural and organic, you can use soapy water to treat smaller pests, such as aphids, thrips, spider mites, flea beetles or whiteflies.

If you see on your tomato plants hornworms or cutworms, I would suggest to handpick them. If you think that it would take you a lot of time, you can use Bt (Bacillus thuringiensis) to get rid of these pests.

Cold Weather

Cold weather is another factor that will cause yellow leaves on your tomato plants. As the season is going to an end, the temperature is dropping, so the tomato plants will get stressed. This will lead to random yellowing in your plants’ leaves.

If the nights are turning cold (under 10°C/ 50°F) you can add mulch around the plants, because the soil will become colder. So, you can protect the roots for longer. If your plants are in pots or growing bags, and you have a shed or garage, you can move your plants in there overnight. Like this, they will not get cold and you can elongate their lives.

Wrap Up

As I mentioned earlier, there are several reasons why your tomato plants can turn yellow. Sometimes it can mean the end of the season or a viral disease. So, there is nothing to do about it. However, there are a few things that you can treat and save your tomato plants.

If you pay attention to the symptoms you can easily solve the problems. You can even learn from it, so next time you can prevent these.



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