Why Are Tomato Seedlings Turning Yellow?

Tomato seeds usually germinate in 5 to 10 days. When seedlings begin to sprout, the first 2 leaves are the cotyledons, which helps the plant to develop and grow healthy. When the plant starts to grow mature leaves, the cotyledons will start to fade and then die.

tomato seedlings turning yellow

However, if you notice that the mature leaves are starting to turn yellow and die, then you should know that something is wrong with your seedling.

Usually, yellowish and faded leaves mean that the seedling is struggling and some essential factors are not suitable to provide healthy growth.

In this article, I will present some of the main reasons why are tomato seedlings turning yellow.


Tomato seedlings are turning yellow if the light is too much or too little.

If you grow your seedlings indoors, then you should provide the right amount and the right intensity of light to make them grow healthy.

Usually, indoor seedlings are best using a grow light placed directly over the plants. Also, this grow light should be kept on for at least 12 hours every day, so, the seedlings can get as much light as needed.

After 12 hours of light, should come 12 hours of darkness. In many cases 12 hours is impossible, but at least 8 hours of darkness is a must. Because as I said, too much light can lead to yellowing seedlings as well.

If you put your seedlings on a window sill, you should pay attention to the intensity of the light because the direct sunlight, which sometimes can be too strong, can burn your seedlings.


If your seedlings are not getting enough water, they can become yellow. These need enough water to grow healthy roots and leaves.

Therefore, you should be consistent in watering your seedlings to avoid problems. You shouldn’t water them every day, but when they need it.

Make sure, the soil is always moist, but not wet. Tomato seedlings hate being overwatered; therefore, overwatering can cause problems such as yellowing seedling as well.

Too much water can drown your tomato plants because these need to breathe, but if overwatered, this is not possible for them. When there is too much water in the soil, the seedling’s roots cannot absorb the needed nutrients, and this is a reason why your seedling’s first set of true leaves are turning yellow.

There are other signs as well when your plant gets too much water. If you see that the seedlings are not growing or the new leaves are brownish or begin to wilt, then you should stop watering them for a while.

Continuing overwatering your plants even if there are clear signs, then these can die because of rotten roots. If the roots are not healthy, the plants cannot be healthy either.


Fertilizing your seedlings can be another reason why they turn yellow. Seedlings don’t need fertilizing at this stage if you use proper soil. Potting soils contain slow-release fertilizer that can feed your seedling for weeks.

However, if you still want to fertilize them, you should do it every 12 to 14 days and make sure to read the label of the fertilizer. I suggest adding half amount of the recommended rate, and NEVER increase it.

Over-fertilizing can kill your seedlings. But how do you know if there is too much of it? If you notice white deposits around the drainage holes, that means you overdone fertilizing. To correct the situation, you should stop fertilizing and you should flush the soil with running water so this can wash away the built-up minerals.

How to Fix Tomato Seedling from Turning Yellow?

When you notice that your seedlings are turning yellow, you should look out for the above reasons. After you find out what is causing the problem, you probably ask yourself: “Ok, and now? What to do?”

First of all, ensure that you use the right soil when you sow the seeds. If you miss this step, then you can replant your seedling after you checked all the other factors.

So, repotting the plants should be the last step in the fixing process because tomato plants’ roots don’t really like to be bothered.

Water your tomato seedlings regularly and don’t leave the soil to dry out completely. Avoid overwatering because this is often the major reasons why your tomato seedlings are turning yellow.

In order to have healthy tomato seedlings, they need enough light. So, you should provide the right amount of light for them. I suggest providing for the indoor seedling a source of light, such as a grow lamp for the best results.

As I mentioned above, tomato seedling at this stage of their lives doesn’t need fertilizing. If you are using potting soil that should contain enough nutrition for your plants.

Sometimes yellow seedlings can be a result of mould and fungus or pests as well. You should check your plants for different diseases regularly and if you think that is the problem, you can treat them with specific sprays.

Wrap Up

If you notice that your seedlings’ leaves are turning yellow don’t get panicked. The first two leaves which are the cotyledons will die after the true leaves are grown out.

However, if the true leaves are getting yellow, that should be a sign of a problem. If you identify and fix the problem in time, you can easily save the seedling.

Remember, enough light and consistent watering is essential for tomato seedlings. Fertilizing is not a must, but if you do it, be cautious with that and avoid overfertilizing.

If you take proper care of your tomato seedlings, these will be thriving and growing healthy and will not become yellow.

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