Why Tomato Plant Leaves Turn Yellow (& How To Avoid This Problem)

Tomatoes are one of the most versatile agricultural products and the list is endless when it comes to this fruit’s use cases. Whether you want to pair them with melty mozzarella as a spread or incorporate them into your skincare routine, tomatoes never fall short of being useful. Aside from vitamins and minerals, tomatoes contain antioxidant lycopene that is said to lower risk of cancer and heart ailments. They are also a good source of fiber, with an average-sized tomato containing about 1.5 grams of fiber. Tomatoes are likewise rich in potassium, which is essential in blood pressure control. Hence, it is no wonder that tomatoes are a must in vegetable gardens.

Just like these low-maintenance dwarf shrubs, tomatoes are relatively easy to grow and maintain. You can grow tomato seedlings in containers and transplant them into their own pots once their leaves start to unfurl. However, you have to be prepared to deal with problems such as wilting leaves, fungus and dark spots. In this article, we will discuss some of the most common challenges when growing tomatoes, including leaves that turn yellow, as well as tips on how to avoid such problems.

Be sure to check out our other article on cucumber leaves as well.

Common tomato plant problems

Identifying the problem of your tomato plants is essential in solving it. Tomato plant problems are commonly caused by diseases, poor cultivation, nutrient deficiencies, insects and fungi. Discoloration of the leaves, fruit production performance and the presence of spots or tiny holes are good indicators of these problems.

Tomatoes that lack proper nutrients or are poorly cultivated may have dark, leathery spots on the bottom of the fruits in a case called blossom-end rot. If you see holes in tomato plant leaves, then these are likely caused by insects. Slugs and flea beetles enjoy feeding on those poor leaves although tomato plants generally outgrow the damage caused by these insects. The presence of white spots on tomato leaves is also a common problem among cultivators. These spots are caused by different factors including humidity and air flow. On the other hand, tomato leaves with dark or brown spots could be suffering from bacterial problems. Some of these problems may even occur in select indoor plants like snake plants or aloe vera. But while these issues may sound like a burden, there are several ways to prevent them from happening.

Why are my tomato plant leaves turning yellow?

If you notice yellow leaves unfurling out of an otherwise healthy set of tomato plants, you are not alone. Many tomato cultivators experience this problem at one point in their gardening journey. This can be attributed to a number of reasons, including but not limited to: lack of sunlight, improper watering habits, soil deficiency, poor nutrients, plant diseases and pests. In some cases, tomato plant leaves turning yellow should not be a cause for concern. But if you are determined to solve this problem or prevent it from ever happening, here are some pointers.

One of the common reasons why tomato leaves turn yellow is nitrogen deficiency in the soil. Experts recommend growing nitrogen-rich plants such as alfalfas, peas and beans in the surrounding area to address this problem. Additionally, you can do a soil test analysis to determine whether nitrogen deficiency is the reason behind those yellow leaves. This can be done by getting a sample soil, which will then be incubated and tested in a laboratory. Another method is by conducting a soil nitrate analysis, which can be carried out either before the planting of the tomatoes or during the growing period.

Yellow leaves are just one of the many problems pests may bring to your tomato garden. In some cases, yellow leaves are accompanied by black spots or tiny holes due to the presence of whiteflies, flea beetles, aphids, spider mites and thrips. These pests tend to inject their saliva into tomato plants as they feed on their leaves, which turn yellow in the process. You can confirm if pest infestation is the main culprit by looking at the leaves’ underside. The damage may also vary depending on the type of pest that fed on the leaves. For example, aphids leave yellow and wilted leaves, while psyllids turn leaf veins into purple and distort the stems. While pests are a headache, the good news is that they can easily be treated using insecticidal soap or spray. These insecticides are readily available at your local stores, but you can also create your own at home. Simply mix vegetable oil with mild soap to have your DIY oil spray insecticide. Speaking of oil, you may want to check out this list if you want to know how you can reuse waste oil and convert it into heat.

Poor watering habits can also lead to yellow, crispy tomato leaves. Tomatoes are heat-tolerant agricultural products that need to be watered gradually. The frequency of your watering routine may vary depending on the type of tomato and where it is planted. For example, tomatoes that are planted in containers may need to be watered once a day, preferably in the morning to ease off the heat. To know more about proper watering habits for tomatoes, check out the succeeding paragraphs.

Another possible cause of tomato leaves turning yellow is lack of sunlight. This is more common among mature plants that are bushy. The upper part of these plants tend to block the sun, leaving the leaves at the bottom half with little to no sunlight. These yellow leaves are unlikely to contaminate healthy leaves so you can either cut them off or just keep them altogether.

Lack of proper air flow can likewise cause yellow tomato leaves. To prevent this, make sure to keep plants 24 to 36 inches away from each other as this will allow proper air circulation. If you are transplanting your tomatoes, make sure to set the root ball deeper than how they were in the pot.

If none of the above answers your question, “why are my tomato leaves turning yellow,” then the likely culprit could be a disease. One of the most common tomato diseases is early blight, which is caused by the plant pathogen, alternaria solani. This disease generally affects tomatoes and potatoes, and is widely notorious in North America.

Older plants are more prone to early blight. This disease starts off with odd-shaped dark spots on mature leaves and then slowly transforms into rings that are surrounded by yellow patches. Early blight usually targets the bottom half of the plant and works upward. If not treated properly, this disease can reduce fruit production and result in complete defoliation. There are several things to keep in mind to prevent early blight from infecting your precious tomato plants. First, make sure to keep proper spacing between plants to allow the passage of air and avoid risks associated with wetness and humidity. Next, consider using a fungicide to protect your foliage. Some of the recommended fungicides contain copper, mancozeb or chlorothalonil. These fungicides, which attack different targets in the fungus simultaneously, should be reapplied to each plant set every one or two weeks. Minimizing the level of moisture on tomato plants also helps in keeping early blight at bay since alternaria solani thrives in a moist environment to germinate. If yellow leaves start to appear, make sure to cut them off and remove the debris right away.

Another fungal disease that causes yellow leaves is verticillium wilt. This soil-borne disease attacks vulnerable plants from their roots before spreading through the vascular system. It can be distinguished from other plant diseases by the brown and yellow patches from the mid-section of the leaf’s vein down to its edges. This disease is notorious as it affects a wide variety of plants including shrubs, trees and perennials. It will begin to manifest through curled leaves, which will eventually turn yellow or brown before falling off. Unfortunately, verticillium wilt has no cure. The impacted plant has no choice but to die once the disease enters it. You can, however, protect other plant sets from getting this disease by immediately destroying the infected plants and rotating your tomatoes into a separate area for the next growing season.

A viral disease called tomato mosaic virus can also cause yellow leaves. This disease starts to manifest through yellow patterns on the infected plant’s leaves. It may also cause the leaves to curl and shrink. This virus generally lasts two years in dry soil or debris. If the soil is moist, the virus can last up to a month. Some of its symptoms may not manifest under cool temperature, so it is best to keep an eye on your plants when moving them to a dry environment. Buying seeds from reputable sellers is the primary way to avoid this virus. Do not hesitate to inquire about their sanitation protocols and inspect transplants before buying. Since the symptoms of tomato mosaic virus may not manifest right away, make sure to wash your hands before and while handling the plants, and clean your garden tools properly.

Other tomato plant diseases and treatments

In this section, we will discuss other common tomato plant diseases that do not necessarily manifest through yellow leaves. If early blight exhibits ring-like dark spots surrounded by yellow patches, late blight shows itself through leaf lesions that look like water-soaked spots, which can be distinguished by the white molds around the edges of the infected area. This disease can lead to defoliation within two weeks after the onset of symptoms. It can be prevented by proper spacing between plants and keeping foliage dry. Like in other cases, make sure to remove and destroy the infected plants to prevent the disease from entering other healthy plants.

Another fungal disease among tomatoes is southern blight. It also attacks weeds and crop plants, and is prevalent in tomato gardens in Oklahoma. Plants tend to wilt rapidly once infected by this disease and show off a lesion on its stem, which will then be covered by white molds called mycelium. Afterward, tiny white spots will appear on the mycelium, before turning brown. Crop rotation is the most effective way to control southern blight. To prevent this disease, consider alternating tomatoes with non-vulnerable crops like corn, while avoiding highly vulnerable ones such watermelon or cantaloupe.

White spots

Another telltale sign that your tomato plant has a problem is the presence of white spots on its leaves. These white spots are called oidium lycopersicum but are commonly known as powdery mildew. These spots typically appear on the leaves, but they can also be found on the stems in extreme cases. They are caused by high humidity, sun damage or fungal disease. Greenhouse-raised seedlings are highly vulnerable to powdery mildew due to the absence of proper air flow. You also have to keep an eye on recently transplanted seedlings as the change of location, including the varying temperatures between indoors and outdoors, could affect the plant.

Aside from sun damage, white spots on tomato leaves may also stem from fungal disease, which is typically caused by overwatering. Fungal spores are stimulated if the soil has excess water, causing common plant problems such as root rot and leaf spots. Tomato plants that do not receive the proper amount of nutrients are also prone to powdery mildew. If your plant is short on phosphorus or calcium, then prepare to see white or yellow spots on its leaves. You can treat infected plants by using a potassium bicarbonate spray. Alternatively, you can make your own spray by combining a drop of liquid soap, one teaspoon of baking soda and two gallons of water. Once done, transfer the mixture into a bottle and thoroughly spray the tomatoes, including the leaf undersides and stems. Aside from these sprays, there are many other things you can do at home to improve your garden. You can even consider investing in machines such as engine-driven welders, plasma cutters and belt sanders if you want to create more garden or farm projects.

Black spots

Another problem that tomato cultivators encounter is the presence of dark brown or black spots on the plant’s leaves. This problem may sometimes look similar to other symptoms that a plant will exhibit if it is infected with a disease. For example, septoria leaf spot is a fungal disease marked by dark spots, a grayish center and yellow patches. While septoria leaf spot is not fatal, its dark spots can enlarge and spread fast, leading to complete defoliation. In some cases, this disease can even lead to cracked fruits when not treated early on. To avoid this, immediately cut off the affected leaves and use clean hands when holding uninfected plants. You can also use organic fungicides containing potassium bicarbonate or copper to prevent the infected leaves from spreading further. For extreme cases, you can consider using chemical fungicides that have chlorothalonil.

If these dark spots are surrounded by a yellow halo, then your tomatoes may be suffering from a plant disease called bacterial speck. These spots often have a diameter of ⅛ to ¼ inch and are more noticeable on the leaves’ underside. You can prevent bacterial speck by using pathogen-free transplants or seeds. When watering, make sure to use a drip hose or a soaker instead of a sprinkler to hydrate your tomato plants. Investing in a reliable drip hose is a wise idea if you are planning to raise tomatoes in your garden. And while you are searching for the right drip hose, you may also want to check out our list of the best plasma cutters, which can be very useful for your DIY projects in the garden!

Brown spots

Brown spots on leaves are another indicator of a poor health status among tomatoes, Looking similar to septoria leaf spot, target spot starts as small dark brown lesions that enlarge to dark brown. Non-experts may find it hard to distinguish this disease from others because of many similarities, including the yellow halo that surrounds the lesions. One thing to look for is the concentric or ring-like pattern of the lesions that tend to eat up the entire leaf. Because it can spread rapidly, target spots need to be removed at the first signs of symptoms. During growth, you can cut off some branches at the bottom part of your tomato plant to improve air flow. You should likewise keep your plants away from weeds, which can be a host of fungus. If the unavoidable happens and your plant gets infected, you can control its spread by crop rotation, allotting up to three years before planting tomatoes in the same area.

Dark spots

Even the healthiest tomato plants can encounter problems when they begin bearing fruits. If you notice dark pots on your tomatoes, then this is probably a case of blossom-end rot, which is triggered by a combination of calcium imbalance and watering issues. This starts off by infecting the water-soaked part of the fruit, which enlarges and turns dark brown before starting to rot. The impacted area can also be distinguished by its sunken and leathery appearance. Tomato plants that grow first during the season are more prone to blossom-end rot, though this condition can occur at any point as the plant matures.

Cut off the affected fruit immediately to prevent it from damaging others. You may also consider using a calcium spray to treat affected areas as well as to protect the rest of your healthy tomato plants. Blossom-end rot can also be prevented by growing your tomato plants in well-drained soil, and by using lime, fertilizer and organic mulches.

Tomato plants not flowering?

While tomato flowers may not be as attractive as these purple flowers on our list, they are nothing short of fancy because they indicate that your plant is set to produce fruits! However, some tomato growers often complain about not having enough fruit set or flowers that do not yield any fruits at all before they even wither. Some of the common causes of this are inadequate light, high temperature levels, insufficient pollination and wrong type of fertilizer.

If your plant is not receiving sufficient light, this may cause nonproduction of fruits in tomatoes as plants in general require six to eight hours of sunlight to yield flowers and fruits. Consider moving your plants to a space where they can get adequate sunlight to encourage fruit production. However, if your tomato plant experiences elevated temperature levels, this may also lead to nonproduction of fruits. While tomatoes thrive in hot climates, too much heat, especially amid dry spells, can interfere with pollination.

To counter this, make sure to keep your plants hydrated.

While tomatoes can pollinate themselves, they may still need some help from pollinating insects like bumblebees to boost production. Tomatoes in greenhouses should have open vents and doors to encourage bee activity. You can also practice artificial pollination by gently shaking the tomato plants to imitate insects’ buzz.

Soil fertility is another factor that influences tomato plants’ fruit production. Potassium-rich organic fertilizer should be fed to the plant once its flowers start to bloom.

Holes in the leaves

Leaves with holes are never a good sign of a plant’s health status. One cause of holes in your tomato plants’ leaves are insects. Cutworms, slugs and flea beetles are just some of the common garden pests that you need to keep an eye on if you are cultivating tomatoes. Flea beetles typically hide underneath the leaflets during winter and come out in spring to feed on those leaves, leaving tiny holes that even a trypophobia would not endure. You can get rid of these pests by spraying insecticide containing organic liquid soap.

Slugs also thrive in spring and are easily attracted to tomato leaves. These nocturnal pests feed on tomato plants by creating oddly shaped holes in their leaves. One way to determine whether a slug is your suspect is by looking for slimy tracks on the leaves and on the ground. If you notice your plant’s stems are being chewed within at least one inch of its base, then the culprit must be cutworms. These pests love to feed on buds, stems and foliage, and measure up to two inches in length.

Earwigs are also notorious tomato leaf-eating pests. They feed on the leaves at night and hide in crevices or under pots when the morning comes. Thankfully, slugs and earwigs can be managed by using homemade traps.

How often should you water your plant?

Like any other organism, tomatoes need water to thrive. However, it is not enough to water your tomato plants whenever and however you like it. Watering your plant too much or too little could cause problems mentioned in this article such as root rot, low fruit production, stunted growth and brown leaves.

Generally, plants need the right amount of water so that it can absorb nutrients, including dissolved sugar, and grow healthily. Water passes through the plant’s root system, all the way to its stem and through the leaves and flowers. But watering routines may vary depending on the type of plant. For tomatoes, it is important to water them deeply and gradually, allowing enough time for the water to enter the moist soil and soak in there. A good indicator is moistened soil of up to 6 to 8 inches in depth. You also have to make sure to water at the tomato plant’s stem or roots rather than its leaves. Always keep in mind to water around the stem and not directly on it as this allows the roots to spread further.

Frequency is also important when watering plants. There really is no black and white rule on how often you should water your tomato plant. One factor to consider is the weather. If it is too hot, you may consider giving your tomato plant water once every three days. You also have to keep an eye on other signs such as wilting and dry soil, although these are not guaranteed indicators that your tomato plant is in immediate need of water. Tomato plants may droop in the middle of the day but they will return back to normal at sunset. However, if your plant remains bent after sunset, then this may be a sign of a parched ground. It is best to water your tomatoes at dawn as it gives the plant enough time to start the process of photosynthesis.

You can utilize a drip hose or a drip irrigation system to water your tomatoes. The latter is highly recommended if you plan to be away for weeks as it allows you to set a schedule. A drip irrigation system also offers a more efficient way of distributing water and allows the soil to gradually absorb the water. Installing your own drip irrigation system is not as easy as setting up your fuel transfer tank at home just like in this article, but once it is in place, you will save a lot on time, water and energy!

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