Written by Ivy
Feb 07 2023
Gardeners who grow tomatoes often become alarmed by yellowing leaves. Yellow leaves on tomato plants are probably caused by nutrient deficiency. On tomato plants, yellow leaves may be an indication that the plant is not getting enough sunlight.
When a plant that was previously healthy changes from green to yellow, it raises alarm and prompts frantic fixes that might actually do more harm than good.
However, tomato gardeners encounter yellow leaves on tomato plants on a regular basis throughout the growing season.
Most of the time, the issue can be resolved quickly (for example, by watering the plants incorrectly) or may not even require any concern.
The most typical causes of tomato leaves turning yellow are these seven problems. Your plants will quickly return to normal once the issue is resolved (if there is one).
Okay, let's just address this one first since it's one of the top concerns for novice tomato growers and isn't at all warranted.
If the leaves below are turning yellow on your young tomato plants or seedlings, do not worry.
These are the seed leaves (also called cotyledons). They are the first leaves to form when the seeds germinate but are not "true" leaves.
These leaves turning yellow and falling off is a normal part of the development process and is in no way cause for concern.
Inadequate watering is the most likely reason for the yellowing of tomato plant leaves. Many gardeners make mistakes with watering, sometimes giving the plant too little water and frequently giving it too much.
Gardeners may overdo it on the care front in an effort to keep the plants happy and give the plant far more water than it actually needs out of concern that the soil will dry out. The roots may become choked and rot as a result of too much water in the soil. The leaves begin to yellow and drop off as a result of the weakened roots and decreased soil oxygen levels.
The leaves' yellowing after wilting is another effect of underwatering. The leaves will start to yellow at the edges if the plant is being underwatered, and eventually the entire leaf will fall off.
Examining your watering practices will probably reveal whether or not watering is the problem. If you have watered when the top layer of soil is still wet, or if the soil has become waterlogged, overwatering is likely the cause. Underwatering is the cause if the leaves are wilting and the plant is having trouble standing up (or if you are aware that you have missed one or more watering sessions).
Correct watering is essential to the health of your tomato plants. Only water the plant when it absolutely needs it, which is usually when the top 1 or 2 inches of soil have dried out. Check the soil every day.
Water in the mornings to prevent any evaporation or damage to the leaves. To completely saturate the soil and promote the development of deep roots, water the area around the roots, not the leaves. Water slowly and deeply.
If overwatering is the cause and the problem does not fix itself, you may be dealing with a bad case of root rot.
Unfortunately, it is very difficult to save plants at this stage. The plant can be dug up, the decayed portions of the roots removed, and new soil added. However, it might be best to start over depending on how much of the root is still present and the plant's growth.
When your tomato plants' surrounding soil is not adequately aerated, a similar issue arises. Because of a lack of oxygen, the roots start to suffocate. The oxygen, water, and other nutrients cannot be distributed throughout the plant by the roots. As a result, the leaves start to turn yellow, which is a sign that the plant is about to die.
You can aerate the soil by hand by loosening it with your hands, depending on how well-established the roots are. However, this is likely to damage the root system and can cause more issues. For the best chance of completely avoiding this issue, start the plant in healthy soil that has been supplemented with organic matter.
Growing tomatoes in raised beds or big pots is one way to address the problem since walking on the soil frequently causes soil compaction.
If you've recently transplanted your seedlings (around a week or two before) and notice yellowing leaves on the bottom of the plant, transplant shock is likely the cause.
When seedlings are moved from a warm spot – indoors or a greenhouse – to cold soil outdoors, they need time to adjust to their new conditions.
Yellowing of the plant's lowermost leaves can result from shock. Fortunately, this period of adjustment will pass quickly. There is no need to be concerned as long as the fresh growth is healthy and green. The plant will eventually lose its yellow leaves and get well again.
As transplant shock is not usually detrimental to the plant, and not necessarily fixable once it is discovered, it's best to prevent the problem instead. Make sure the soil has warmed up before transplanting, and that nighttime lows (below 50F) are avoided.
If the plant exhibits symptoms of transplant shock, you can help it recover by cutting off the yellowing stem leaves. By doing this, the energy will be focused on the desperately needed new growth rather than on trying to revive withering leaves.
Disease is one of the more sneaky factors that contribute to yellowing leaves. Yellow leaves are a symptom of a number of diseases that affect tomato plants, many of which are challenging to treat once they have developed.
The first culprit is early blight, caused by a fungus in the soil. Fortunately, this issue is simple to identify. In the lower leaves, a pale-yellow spot will appear, turning into a dark brown patch with yellow at the edges. The whole leaf will turn yellow and fall off if unattended to.
Similar markings appear due to another fungal disease, Septoria leaf spot. Large brown spots connected by yellow patches will appear on the leaves of tomato plants infected by this fungus. If left unattended, the issue could spread from the plant's leaves to its stem, resulting in even more harm.
Then there are the various "wilts" like Bacterial, Fusarium, and Verticillium wilt.
The roots of the plant become infected by fusarium wilt infected in the soil, which prevents water from reaching the plant's stems and leaves. Even though there is sufficient water in the soil, the plant will appear to be wilted, and its leaves will start to fall off from the bottom up.
Verticillium wilt symptoms resemble those of early blight and septoria leaf spot. On the lower leaves, pale yellow spots begin to develop, surrounded by brown veins. The spots will eventually turn brown, and the plant's leaves will drop off.
Less common is Bacterial wilt, caused by a bacterium commonly found in sandy soils when they are moist. However, symptoms usually don't appear until later in the season after transplanting. Suddenly, the plant's leaves begin to turn yellow, and it begins to wilt.
You must act right away if your tomato plants exhibit any disease symptoms. If left untreated, the problem can spread to the rest of your plant, and to other parts of your garden.
Early detection is key to managing early blight and Septoria leaf spot. Keep the damaged leaves away from other plants in your garden and remove and discard them. Apply a fungicide made to address the problem, adhering strictly to the product's directions until the situation gets better.
The plant must be immediately discarded if it develops any of the three "wilts," unfortunately. None of these illnesses are curable, and if given the chance, they will all spread throughout your garden. In order to prevent spreading, be careful not to touch any other plants when removing the afflicted plant.
There are steps you can take to reduce your risk even though there is no guaranteed way to prevent disease-related issues. Give each plant enough room so the leaves do not touch, and choose varieties that are more resistant to these ailments. For healthy soil, clean your gardening tools frequently, and rotate your crops.
Your leaves may be suffering from a nutrient deficiency if none of the previous issues can be blamed for them. There may not be enough of a particular macro- or micronutrient in the soil, or the plant may be having trouble absorbing that nutrient.
Nitrogen is the primary macronutrient responsible for the yellowing of leaves.
For a plant to grow well and produce leaves, nitrogen is necessary. The older leaves start to turn a pale yellow when the plant does not get enough nitrogen. Lack of nitrogen is the cause if the plant appears to stop growing after this time.
Chlorosis, a condition that results from a deficiency in specific micronutrients, can also make the leaves turn yellow. When the tomato plant lacks access to micronutrients essential to photosynthesis – magnesium, iron, sulfur, or zinc – it cannot produce chlorophyll. While the veins continue to be bright green, this results in the leaves turning yellow.
Apply a general fertilizer if you think that nutrient deficiency is the issue. The majority of general fertilizers will have a balance of nutrients to make up for any nutrient deficiencies in the soil.
It is best to perform a soil test to be sure. This will confirm the origin of the problem and allow you to fix it with a targeted solution.
For instance, applying an Epsom salt solution to the leaves can help treat a magnesium deficiency. Without a soil test, you cannot be certain that there is a deficiency and risk further harming the plant by making unnecessary repairs.
A soil test will also reveal whether the issue is with the soil or the plant. Keep in mind that a plant's nutrient deficiency is not always due to a soil issue. Instead of a problem with the soil specifically, there may be a problem with the plant's roots that prevent them from transporting nutrients throughout the plant.
If the soil test confirms no deficiency in the soil, examine your watering habits and the aeration in the soil to fix the problem.
Examine the season before rehashing any of these situations and making a million fixes.
Is tomato season over yet? In that case, yellowing leaves are not alarming. Instead, they indicate the end of production as a natural part of the plant's life cycle.
You can prune any new growth and dying leaves once the leaves begin to fall off in order to hasten the ripening of the plant's last set of fruits.
Don't panic is the first piece of advice for any gardening situation.
You will likely be able to identify the problem that is most likely to exist based on the warning signs listed here, your examination of the plant, and your daily maintenance practices.
Always proceed slowly when attempting to address issues with yellowing leaves to give the plant time to adjust before continuing with a different solution. If a disease is the cause of the issue, you must take immediate action (fortunately, diseases are typically easier to identify).
It is a trial-and-error game. If a fix doesn't work, try another one gradually until the plant is back to normal. You'll soon be able to diagnose issues with tomato plants successfully and solve them without difficulty.
Removing some of the tomato plant's leaves will help it cope with the situation if the yellow leaves are a result of environmental factors or a nutritional deficiency. The remaining leaves and fruits can be supported by the plant's energy. Remove the leaves from the tomato plant and throw them in the trash if the yellow leaves are caused by a bacterial or fungal disease. Make sure those leaves aren't composted. Sterilize the gardening scissors used in removing the yellow, infected leaves before using them again.
With the exception of soil-borne fungus, tomato plants grown in pots or in the ground are both susceptible to the same types of stresses. On an apartment balcony or patio, small container gardens frequently have better, nutrient-rich soil, which results in healthier tomato plants.
Regardless of the size of your vegetable garden, keep an eye out for signs of plant stress, which frequently manifests first as tomato plants' yellow leaves.