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Tomato Seedling Leaves Turning Yellow — What’s Causing It?

So, you have finally decided to move forward with growing a tomato garden, but there’s one tiny problem: the tomato seedling has leaves that are starting to turn yellow.

Is that good or bad? What causes the leaves to be yellow? How do you fix it?

While there are several reasons for a tomato seedling’s leaves to turn yellow, this seems to be a common scenario that can be resolved.

Fortunately, you may have caught the problem in time, if the rest of the plant appears to be in good overall health.

A tomato plant with yellowing leaves can usually be saved with just a few simple tweaks to your gardening technique.


Tomato Seedling Leaves Turning Yellow

Tomato seedling leaves turning yellow may be due to a lack of sufficient calcium and iron. Too little or too much watering, lack of sunlight, and diseases can also cause yellow leaves. However, yellow leaves are sometimes a normal part of development for tomato plants.


Nutrient Deficiencies Can Cause Leaves to Turn Yellow

Although tomatoes are one of the most popular crops to grow, they are very high maintenance. Tomato plants feed heavily on the nutrients in the soil, which can easily lead to deficiencies.

While lack of adequate nitrogen is the most likely culprit, especially if the entire leaf is turning yellow, newly sprouted leaves are more likely to be deprived of calcium and iron.

While you can usually resolve this issue by switching to high nitrogen fertilizer, you should conduct a test on a soil sample to determine exactly which nutrient, if any, that the soil is lacking.

Of course, more nitrogen won’t make a difference if the plant needs more iron.


Too much or Too Little Watering Can Cause Yellow Leaves

Balance is a key factor when watering tomato plants, as overdoing or underdoing the watering will result in the plant showing signs of nutrient deficiencies, such as yellowing leaves.

While it may be tempting to go out in the garden with a watering can every day, this isn’t the best course of action when it comes to caring for tomato plants.

Tomato seedlings do fine with just an inch of water per week at the beginning of the season and two inches once they begin to produce fruit.

Tomato plants shouldn’t be watered more often than two times per week, but you should always strive for deep watering to allow your tomato plant the opportunity to absorb as many nutrients as possible.


Lack of Sunlight Can Cause Yellow Leaves

If only the underside of the leaves is turning yellow, or the yellowing is only affecting one side of the tomato plant, the cause may simply be a lack of sunlight.

Naturally, the side of the leaf that is facing the soil isn’t going to get as much sunlight as the top of the leaf. While there isn’t much you can do to resolve that situation, it isn’t anything that you need to worry about.

Now, if only one side of the entire tomato plant is turning yellow, you may need to begin rotating the pot, so that both sides of the tomato plant will have daily access to sunlight.


Diseases Can Cause Leaves to Turn Yellow

This doesn’t mean that your tomato plant is doomed, as diseases are common on tomato plants. Besides, there are other explanations for the yellowing leaves.

It doesn’t necessarily signify disease. However, disease is one possible reason for your tomato seedling turning yellow.

There are a few fungal diseases that commonly occur on tomato plants, such as Septoria and Early Blight, both of which can cause yellowing leaves.

There are also some wilting conditions that cause leaves to turn color and start to become wilted.

Fortunately, these diseases can be resolved with early detection, the removal of affected leaves, and treatment with a fungicide.


Yellow Leaves May Be Perfectly Normal

Yes, it is normal for the leaves of tomato seedlings to turn yellow. When a tomato plant produces its very first leaves, which are referred to as seed leaves (or cotyledons).

These initial leaves will turn yellow and end up falling off the plant before being replaced with new leaves. This is absolutely normal for tomato plants.

Tomato plants are also known for developing yellow leaves at the end of the season, following harvest, which is perfectly normal, as well.

Two other common reasons for leaves turning yellow are the soil being compacted too tightly, and transplant shock after repotting tomato seedlings.


Frequently Asked Questions about Tomato Seedlings Turning Yellow


Should I Cut off Yellow Leaves on Tomatoes?

If the yellowed leaves are seed leaves, they will fall off on their own and not cause the plant harm, but yellowing leaves can be a sign of disease and nutrient deficiencies. Removing the yellow leaves can help prevent to spread of disease to the rest of the plant and prevent a deprived leaf from draining nutrients from the rest of the plant.


Fixing Yellow Leaves on a Tomato Plant

If you notice yellow leaves on the lower half of your new tomato plant, it could be due to nitrogen deficiencies in the soil, in which case fertilizer or compost may resolve the issue.

So, back to the question at hand: why are the tomato seedling leaves turning yellow? It’s hard to say.

It could be the result of nutrient deficiencies, improper watering, diseases, or it may be completely normal.

If your tomato plant has yellow leaves, monitor the plant closely, alter the watering routine, loosen the soil, and rotate the plant.

If it doesn’t resolve on its own, remove the discolored leaves and buy some fungicide.

Tomatoes are a delicious garden staple, but they are prone to disease and need just the right amount of water.

If you notice yellow leaves on your tomato seedlings, it is probably nothing to get worked up about, just your high-maintenance plant begging for some extra TLC.

Author Bio

Daniel Iseli

Taking care of houseplants and gardening are my greatest passions. I am transforming my apartment into an urban jungle and am growing veggies in my indoor and outdoor garden year-round.