Yellow Leaves On Tomato Plants – 10 Reasons And Treatment Tips

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Yellow Leaves On Tomato Plants

Yellow leaves on tomato plants are a very common issue for tomato growers.

There are many reasons why tomatoes might develop yellow leaves, including nutrient deficiencies, insect damage, fungal infections, and even drought stress.

But most importantly, yellow leaf symptoms indicate that the plant has become stressed due to environmental conditions or diseases.

If you notice yellowing leaves on your tomato plants, then it’s important to identify the reason before it becomes a bigger problem. In this article, we will look at the causes of yellow leaves on tomato plants, as well as how to treat and prevent such issues.

1) Nutrition Is The Number One Cause Of Yellow Leaves On Tomato Plants

First off, in most cases, tomato plant leaves turn yellow because of nutritional deficiency.

Tomato plants are heavy feeders, requiring a lot of nutrients, e.g. twice the amount needed for cucumbers and four times the amount required for beans.

It’s good to know that the yellowing of the lower or older leaves is due to the deficiency of mobile nutrients, while the yellowing of the upper or younger leaves is caused by the deficiency of immobile nutrients.

The logic behind this is that mobile nutrients, which move easily inside the plant, are taken upward to the younger leaves so that they stay green, while the older leaves become yellow.

On the other, immobile nutrients stay closer to the roots after they have been taken up and thus the upper leaves become yellow (not having enough of the nutrient).

Mobile nutrients: nitrogen, phosphorus, potassium, magnesium

Immobile nutrients: calcium, iron, manganese

Nitrogen Deficiency Is The Most Common Culprit

Older leaves at the bottom of the plant turn yellow and fall off because the whole plant simply doesn’t get enough nitrogen and thus the younger leaves are “prioritized” in getting nitrogen. The plant also stops growing when there is a lack of nitrogen.

Treatment:

Add nitrogen-rich fertilizer to the soil. But be careful with chemical fertilizers because they can overfeed your plant causing vigorous leaf growth while not producing enough flowers and fruit.

If you want to play it safe, add some organic fertilizer (e.g. compost), which the plant can handle regardless of the volume (you can grow tomatoes even in pure compost).

Iron Deficiency

If the yellowing of the leaves is caused by an iron deficiency, then this will be most noticeable in the younger leaves, usually by way of interveinal chlorosis where the leaf tissue turns yellow while veins remain green.

Treatment:

Lack of iron in the soil is very rarely the case. The problem is very often about the plant having difficulty absorbing iron from the soil because of a number of soil conditions, e.g. the soil is too alkaline (pH greater than 7), too compacted, or too high clay content.

Therefore treatments can be reducing the pH, loosening the soil, or adding organic matter respectively.

Magnesium deficiency

A magnesium deficiency can also produce interveinal chlorosis—here yellowing looks more similar to speckles or spots on the lower, older leaves with green veins between them.

Treatment:

Apply Epsom salts (magnesium sulfate) either through the drip system or as a side dressing (adding it to the side of the stems). Use the amounts recommended by the manufacturer.

yellow tomato leaf, magnesium deficiency
Tomato leaf chlorosis due to magnesium deficiency

Sulfur deficiency

The upper (younger) tomato leaves become pale green or yellow first and then the lower leaves may turn yellow as well if the deficiency prevails. The leaves appear chlorotic, but the veins are reddish, while the rest of the leaf turns pale green or yellow. Another sign is the stem becoming thin and purple.

Treatment:

Put a thin layer of compost or matured manure (1-2 in / 3-5 cm) on the soil surface or add a fertilizer mix containing sulfur (S) to the soil (be careful when mixing into the soil not to damage the stem and roots).

Potassium (potash) deficiency

If there isn’t enough potassium (K) in the soil, the lower (older) leaves towards the margin will turn from green to yellow, then to brown, look burnt, and curl.

Important note: Too low (below 60°F / 15°C) or too high (90°F / 32°C) temperatures can also prevent the plant from taking up potassium even if your soil contains enough of it. Therefore a soil test is recommended to find out whether the real issue is potassium deficiency.

Treatment:

Add potassium to the soil in an organic form such as banana peels, compost, or kelp (dried ocean seaweed without fish emulsion) diluted in water, as a weak solution, either via the drip system or spraying it on the leaves.

You can also add potassium chloride (KCl) 0-0-61 to the soil, but note that it increases the salt level in the soil. Although tomatoes are relatively salt tolerant, this may cause salt damage, especially with container gardening.

Water abundantly your tomatoes planted in pots or grow bags until water starts draining at the bottom to wash away excess salts.

Soil test

Measuring the pH level and the amounts of nutrients in your soil will help you find out what kind of nutrients may be missing or difficult for the plants to absorb.

The soil pH level is an important factor because it affects how nutrients are absorbed by the plant. If the soil is too acidic, then the plant won’t be able to take in enough calcium and magnesium.

Alkaline soils limit the amount of iron that the plant absorbs. Tomatoes require a slightly acidic soil of pH between 6.0 and 7.0.

All in all, if you use special tomato fertilizer products, they most probably contain nutrients that can handle yellow foliage problems.

tomato plant yellow leaves

2) Tomato Leaves Turning Yellow Due To Diseases

In many cases, the yellowing of tomato leaves is caused by diseases, which are, to tell you the truth, hard to handle once they have been established.

Basically, there are two main disease categories that can cause yellowing leaves on tomato plants:

  • leaf spots
  • and wilt.

If you discover the symptoms early, you have a better chance to help the plant recover.

How To Treat Tomato Leaf Spots?

Any kind of leaf spot is likely a sign of disease, e.g. early blight, Septoria leaf spot, and bacterial spot. If discovered early, you can tackle the issue simply:

  • Pinch off the diseased leaves and burn them or put them in the trash.
  • You can remove up to a third (but not more) of the plant’s leaves if you catch the disease early.
  • Keep leaves dry to avoid spreading the disease.
tomato leaves turning yellow, leaf spots

Early Blight

This fungal infection starts out looking like small, circular dark spots on the surface of the lower leaves. As it spreads, the area around the injury grows darker and larger, eventually forming a large, concentric blotch usually yellow at the edges.

It can cause serious damage to plants and thrives in wet conditions. If left untreated, the disease can kill off your entire plant. Fortunately, there are some ways to prevent and control it.

Treatment:

If you notice that your tomato plants have been infected with early blight, immediately take action. First, cut away the diseased leaves. Then throw them in the trash.

Do not compost them because they contain the pathogen. You can also spray the plant with a fungicide. You can use a product like Bordeaux mix, which contains copper sulfate, mancozeb, and propiconazole. Be sure to follow the directions carefully.

Septoria Leaf Spot

Septoria leaf spot is caused by a fungus named Septoria lycopersici. Small spots appear with dark brown margins and greyish centers. When the spots become numerous, the leaves turn yellow and then brown, and finally, fall off.

The spots are most common on older leaves, especially those located near the base of the plant.

Treatment:

Remove the infected leaves immediately and dispose of them. You can also spray the affected plant with a fungicide specifically for treating Septoria leaf spot. Follow the directions carefully until the problem is resolved.

Bacterial spot

Bacterial spot, caused by pathogens belonging to the genus Xanthomonas, occurs mostly in warm, wet climates, as well as in greenhouses. It can affect any part of the tomato plant above the ground, i.e. leaves, stems, and fruit.

Bacterial spots are small (less than ⅛ inch | 3 mm), first light green or yellow then turning brown. If the disease is severe, the leaves may turn yellow and fall off completely.

Treatment:

If you discover the disease early, you can remove the affected leaves. However, bacterial spots basically cannot be cured and the following is suggested:

“Remove symptomatic plants from the field or greenhouse to prevent the spread of bacteria to healthy plants. Burn, bury, or hot compost the affected plants and DO NOT eat symptomatic fruit.” Michelle Marks, UW-Madison Plant Pathology

How To Treat Tomato Wilt Diseases?

There is no cure for wilts if the plants are wilting due to a pathogen. You need to remove and destroy the affected plants.

Bacterial Wilt

It occurs due to the Ralstonia solanacearum bacteria infection via the soil. The infected plant, likely later in the season, will start showing light green or yellowish foliage and wilted leaves (usually the youngest at first).

The infected tomato plants will never recover from this disease. The plant will die and the fruit will drop off.

If you notice these symptoms, you should immediately take action and get rid of the diseased plant.

Verticillium Wilt

Verticillium wilt is a soil-borne fungal disease that causes wilting and death of leaves on infected plants. The symptoms include yellowish (and later brownish) V-shaped areas on the older leaves that narrow towards the center of the leaves.

There is no cure for verticillium wilt. You should destroy the plant immediately. Do not use pesticides to control the disease.

Fusarium Wilt

Fusarium wilt is a soil-borne fungal disease caused by Fusarium oxysporum f. sp. lycopersici. It most commonly appears only in the mid to late growing season.

Fusarium wilt causes the plant to wilt often on just one side of the plant or branch. The affected leaves droop and turn yellow, then brown and the plant slows down in growth.

There is no known treatment for fusarium wilt. Discard the plant as soon as you discover the disease.

Can I Compost The Affected Plants?

If you want to play it safe, avoid composting plants that have become infected with any kind of virus, bacterium, or fungus because they may survive the composting process.

Although hot composting, maintaining the temperature of the compost pile over 131°F / 55°C for 3 consecutive days, is said to kill all pathogens, there is probably no guarantee that you can apply that 100% in your home garden.

tomato plant leaves turning yellow

3) Watering Problems

Overwatering

Tomato plants require lots of water to grow properly. But too much water causes problems, especially root rot. If the soil becomes soggy and the oxygen levels drop, it is suffocating the roots, which may rot in the end. If the leaves don’t get enough oxygen, they will start turning yellow and drop off.

Not enough water

Make sure you’re providing enough water. Tomatoes love moisture and won’t do well without it. Keep the soil evenly moist all the time.

Water deeply, soak down into the root zone, don’t just sprinkle on the surface of the soil.

4) Soil Compaction

If the soil gets too dense (e.g. by walking on it), the roots can’t expand and grow, and neither can they take up enough oxygen or nutrients. This can cause the leaves to turn yellow.

Treatment:

You can try to loosen the soil with your hands or with a garden fork, but be very careful not to hurt the roots.

It’s best to prevent the issue by planting into crumbly, loose soil or into a potting mix that ensures proper aeration.

5) The Seed Leaves (Cotyledons) Are Turning Yellow

Once tomato seedlings emerge from the soil, they quickly develop seed leaves—the first leaves a seed plant produces.

They provide nutrients to the developing seedling until true leaves appear. After that, seed leaves are no longer needed. They begin to turn yellow and fall off. That’s perfectly normal.

So if you see yellowing seed leaves (cotyledons) on your tomatoes, don’t panic.

In fact, it’s actually good news: when the seed leaves start to turn yellow, it signals that the plant is starting to develop true leaves. It’s developing!

6) Transplant Shock

Transplant shock happens when the tomato seedling is moved from its small container into a bigger one or the garden soil outside.

This usually causes some stress to the plant, which can result in yellowing leaves. The symptoms may be mild or severe depending on the severity of the transplant shock.

Transplants can take up to 2-3 weeks to fully recover from transplant shock.

If you’re experiencing transplant shock, here are some tips to help alleviate the problem, i.e. give that extra care to your plants.

  • Keep the soil moist during this transition period.
  • Water the plant thoroughly once it’s outside.
  • Fertilize the plant regularly.
  • Give the plant plenty of light.
  • Use a shade cloth to protect the plant from direct sunlight until it acclimates to outdoor conditions.

To avoid transplant shock, harden off your seedlings properly:

  1. For 1-2 weeks, take them outside for a couple of hours per day when the weather is nice.
  2. Protect them from the wind and don’t put them in direct sunlight at first.
  3. You can expose the plants to direct sunlight for the last days of the hardening-off period.

7) Not Enough Sunlight

Tomato plants need sunlight to grow healthy, green leaves. But sometimes, when there isn’t enough sun, tomatoes may develop yellow leaves. This happens because the plant needs light to produce chlorophyll, which gives the leaves their dark green color.

Even though the plants are in full sun, the lower leaves may turn yellow because they’re not receiving enough direct sunlight.

Treatment:

Make sure the tomato gets enough light, which is at least 6-8 hours of direct sunlight per day. Keep weeds and other vegetation away from the tomato so that it has access to direct light.

8) Yellow Leaves On Tomato Seedlings

If your newly purchased tomato seedlings have a little yellow foliage, it probably isn’t a big issue. They just didn’t have the ideal conditions in the nursery to grow nicely, e.g. not enough growth space, light, or nutrients.

Solution:

Provide your transplants with everything they need when planting into your garden soil, raised bed box, or container and the yellowing issue should cease. This includes proper hardening off, fertilizing, watering, temperatures, and enough sunlight.

9) Garden Pests Causing Tomato Leaves To Turn Yellow

Some garden pests, especially insects, can cause tomato leaves to yellow. These include aphids, whiteflies, thrips, mealybugs, and spider mites.

They usually feed on the sap contained within the leaves. Unlike the yellowish discoloration caused by diseases, this type of yellowish color will be localized around the affected part of the plant rather than spreading throughout the entire plant.

Treatment:

Pick off infested leaves and spray the affected area with insecticidal soap or horticultural oil. Insecticidal soap kills insects without harming beneficial insects such as bees and butterflies.

10) The Growing Season Is Over

yellow leaves on tomato plants

As fall arrives, and the gardening season comes to a close, it’s completely normal for tomato plants to start turning yellow. Once the temperature drops, the plant begins to slow down and stop producing fruit.

If there are still a few green tomatoes left on the plant, you’ll want to trim off the yellow leaves and remove any small tomatoes and new blossoms that might be growing.

This will help focus the plant’s attention on the final few tomatoes of the season, and ensure that those tomatoes finish ripening properly.

What Can You Do To Stop Tomato Leaves From Turning Yellow?

All that said, the best way not to encounter yellow leaves on your tomato plants is to keep in mind a number of things and act accordingly.

To avoid diseases:

  • Remove the lower leaves after transplanting (up to one-third of the foliage). If you see any leaves turning yellow or showing spots, remove them immediately.
  • Mulch to prevent soil from splashing onto the leaves (weed seed-free materials, e.g. grass clippings, straw, tree leaves, woodchips).
  • Water the bottom, not the leaves.
  • Ensure air circulation between plants and through the foliage (proper planting distance, staking, and pruning).
  • Clean your gardening tools.
  • Apply crop rotation: don’t plant tomatoes and other nightshades in the same spot within 3-4 years.
  • Wash or bleach previously used containers, cages, trellises, and stakes.
  • Grow disease-resistant varieties.

To avoid nutritional deficiency:

  • Feed your tomatoes with compost, compost tea, worm castings, fish emulsion, manure, or other organic fertilizers rich in minerals. You can use chemical fertilizers, too, but make sure you apply them properly following the instructions.
  • Water your tomatoes regularly keeping the soil evenly moist. Avoid overwatering as well as underwatering.
  • Don’t compact the soil by stepping on it, or use a growing mix in containers and garden boxes that provide the roots with enough oxygen.

To avoid environmental shock or pest stress:

  • Don’t plant your tomatoes in shady spots, let them sunbathe at least 6-8 hours per day.
  • Harden off your seedlings before planting them outside.
  • Remove pests as soon as possible and use organic pesticides.
  • Grow companion plants (e.g. marigolds, garlic, chives) to repel harmful insects.
  • Spray your tomato plants regularly with organic pesticides.

FAQ

Are yellow leaves on my tomato plants a sign of something serious?

It depends. If the problem is caused by nutrient deficiency, then it is not serious and can be fairly easily addressed. However, if the problem is caused by disease or overwatering, then it could be more serious and require more attention.

Should I cut the yellow leaves off the tomato plant?

Yes, it helps prevent diseases from spreading throughout the entire plant and also helps it recover faster. Do not remove more than one-third of the foliage from your tomato plants.

Can tomatoes recover from yellow leaves?

Yes, but it’s best to take action quickly. Remove the yellow leaves as soon as you see them. In most cases, yellow leaves won’t turn back to green, that’s why it’s better to get rid of them.

Why are my greenhouse tomato seedlings turning yellow?

There can be a number of reasons, but here are the most likely ones: 1. They’re not getting enough light. 2. They lack nutrients, most probably nitrogen. 3. They are overwatered. 4. They are underwatered. 5. They are overfertilized with chemical fertilizers.

What causes yellow leaves on tomato plants?

Yellow leaves on tomato plants can be caused by a variety of factors, including nutrient deficiencies, too much or too little water, sunscald, and disease.

How can I prevent yellow leaves on my tomato plants?

To prevent yellow leaves on your tomato plants, make sure to provide adequate water and nutrients, avoid over-fertilizing, and provide the right amount of sunlight. Additionally, regularly inspect your plants for signs of disease and pests.


In summary, if you have yellow leaves on your tomato plant, try to find out what caused it first.

You can help your tomato plants recover if yellowing leaves are a result of environmental issues, e.g. overwatering, nutritional deficiency, or not enough sunlight. In such cases handle the problems with patience as the plants may need some time to get OK.

On the other hand, if diseases are the culprit, take action quickly and use organic pesticides to prevent the spread of the disease. Additionally, make sure to remove pests as soon as possible and grow companion plants to repel harmful insects.

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AUTHOR

I'm a keen hobby gardener. I love growing fruits and vegetables, especially tomatoes. I'm also a certified instructor of the Square Foot Gardening Foundation.