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

Tomatoes are one of the most versatile agricultural products. The list is endless when it comes to this fruit’s use cases. You want to pair them with melty mozzarella as a spread or incorporate them into your skincare routine. They never fall short of being useful. Aside from vitamins and minerals, they contain antioxidant lycopene that lower the 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. They are likewise rich in potassium, essential in blood pressure control. Hence, it is no wonder that they are a must in vegetable gardens.

tomato seeds on metal background

Like these low-maintenance dwarf shrubs, they are relatively easy to grow and maintain. You can grow seedlings in containers and transplant them into their pots once their leaves start to unfurl.

You have to be prepared to deal with problems such as wilting leaves and dark spots. We will discuss some of the most common challenges when growing them, including leaves that turn yellow. Here are tips on how to avoid such problems.

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

tomato that is still growing

Common problems

Identifying the problem is essential in solving it. Diseases and poor cultivation commonly cause tomato problems. Nutrient deficiencies and insects are common problems, too. Discoloration and 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 fruits. It’s a case called blossom-end rot. If you see holes in tomato plant leaves, these are likely caused by insects. Slugs and flea beetles enjoy feeding on those poor leaves.

They generally outgrow the damage caused by these insects. The presence of white spots is also a common problem among cultivators. These spots are caused by different factors, including humidity and airflow.

On the other hand, ones with dark or brown spots could be suffering from bacterial problems. 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 they turning yellow?

You are not alone if you notice yellow leaves unfurling out of an otherwise healthy set of tomato plants. Many cultivators experience this problem at one point in their gardening journey. This can be attributed to several reasons. Some of them include but are not limited to:

  • lack of sunlight
  • improper watering habits
  • soil deficiency
  • poor nutrients
  • diseases
  • and pests

In some cases, it 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 leaves turn yellow is nitrogen deficiency in the soil. Experts recommend growing nitrogen-rich plants such as alfalfas and beans in the surrounding area to address this problem. 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 of soil, which will then be incubated and tested in a laboratory. Another method is conducting a soil nitrate analysis, which can be carried out before the planting or during the growing period.

Yellow leaves are just one of the many problems pests may bring to your garden. They are sometimes accompanied by black spots or tiny holes due to whiteflies and flea beetles. Aphids and spider mites may also cause them. These pests tend to inject their saliva into plants as they feed on their leaves, which turn yellow in the process. You can confirm if the pest infestation is the main culprit by looking at the leaves’ underside.

The damage may also vary depending on the type of pest causing the issue. Aphids leave yellow and wilted ones, 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.

Mix vegetable oil with mild soap to spray your DIY oil insecticide. You may want to check out this list to know how to reuse waste oil and convert it into heat.

little girl watering tomato plants

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

Another possible cause of leaves turning yellow is lack of sunlight. This is more common among mature plants that are bushy. The upper part tends to block the sun, resulting in those with little to no sunlight in the bottom half. These yellow leaves are unlikely to contaminate healthy ones, so you can either cut them off or keep them all together.

Lack of proper airflow can likewise cause it. 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 them, make sure to set the root ball deeper than how they were in the pot.

The above answers may not have satisfied your curiosity about why your tomato leaves turn yellow. If so, the likely culprit could be a disease. One of the most common diseases is early blight, 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 with odd-shaped dark spots on mature leaves and slowly transforms into rings surrounded by yellow patches. Early blight usually targets the bottom half and works its way upward.

This disease can reduce fruit production and complete defoliation if not treated properly. There are several things to keep in mind to prevent early blight from infecting your precious plants. First, keep the proper spacing between them to allow air passage and avoid risks associated with wetness and humidity.

Next, consider using a fungicide to protect your foliage. Some of the recommended fungicides contain copper or chlorothalonil. These fungicides attack different targets in the fungus simultaneously. They should be reapplied to each set every one or two weeks.

Minimizing the moisture level also helps keep 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.

fiskar pruner

Another fungal disease that causes them to turn yellow 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 various plants, including shrub 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 protect other plant sets from getting this disease. It’s done 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 parts. It may also cause them 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 temperatures. Watching your plants when moving them to a dry environment is best.

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. The tomato mosaic virus symptoms may not manifest right away. Make sure to wash your hands before and while handling the plants. Clean your garden tools properly.

tomato seeds

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Other diseases and treatments

This section will discuss other common diseases that do not necessarily manifest through yellow leaves. Suppose early blight exhibits ring-like dark spots surrounded by yellow patches. Late blight shows itself through leaf lesions that look like water-soaked spots. It can be distinguished by the white molds around the edges of the infected area. This disease can lead to defoliation within two weeks after symptoms. It can be prevented by proper spacing and keeping foliage dry. Ensure and destroy the infected plants to prevent the disease from entering other healthy ones.

Another fungal disease is southern blight. It also attacks weeds and crop plants and is prevalent in gardens in Oklahoma. They tend to wilt rapidly once infected by this disease and show off a lesion on their stem. It 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. Avoid highly vulnerable ones such as watermelon or cantaloupe.

White spots

Another telltale sign that your 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 airflow. You also have to keep an eye on recently transplanted seedlings as the change of location. It includes their varying temperatures indoors and outdoors, which could affect the plant.

Aside from sun damage, white spots may also stem from fungal disease. It is typically caused by overwatering. Fungal spores are stimulated if the soil has excess water, causing common problems such as root rot and leaf spots. Ones that do not receive the proper nutrients are prone to powdery mildew. If they are short on phosphorus or calcium, then prepare to see white or yellow spots.

You can treat infected plants by using a potassium bicarbonate spray. You can also make your 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 them. Make sure also to spray the leaf undersides and stems. Aside from these sprays, you can do many other things at home to improve your garden. Suppose you want to create more garden or farm projects. You can even consider investing in machines such as engine-driven welders or plasma cutters.

Black spots

Another problem that cultivators encounter is the presence of dark brown or black spots on the leaves. This problem may sometimes look similar to other symptoms that it will exhibit if it is infected with a disease. Septoria leaf spot is a fungal disease marked by dark spots and a grayish center. You’ll also see yellow patches. While septoria spot is not fatal, its dark spots can enlarge and spread fast.

It leads to complete defoliation. This disease can even lead to cracked fruits when not treated early on in some cases. To avoid this, immediately cut off the affected parts and use clean hands when holding uninfected plants. Use organic fungicides containing potassium bicarbonate or copper to prevent the infected leaves from spreading. For extreme cases, use chemical fungicides that have chlorothalonil.

Suppose a yellow halo surrounds these dark spots. 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 leaf’s underside. You can prevent bacterial specks by using pathogen-free transplants or seeds. When watering, make sure to use a drip hose or a soaker instead of a sprinkler when hydrating.

Investing in a reliable drip hose is wise if you plan 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. It can be very useful for your DIY projects in the garden!

Brown spots

Brown spots on leaves are another indicator of poor health status. Looking similar to the septoria spot, the 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. It includes 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.

You can cut off some branches at the bottom during growth to improve airflow. You should keep your plants away from weeds, which can be a host of fungi. Suppose the unavoidable happens, and they get infected. You can control its spread by crop rotation, allotting up to three years before putting anything in the same area.

Dark spots

Even the healthiest plants can encounter problems when they begin bearing fruits. Maybe you notice dark spots. This is probably a case of blossom-end rot triggered by a combination of calcium imbalance and watering issues. This starts 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. Ones that grow first during the season are more prone to blossom-end rot. However, this condition can occur at any point as it 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 and protect the rest of your healthy plants. Blossom-end rot can also be prevented by growing your plants in well-drained soil and using fertilizer and organic mulches.

Not flowering?

Tomato flowers may not be as attractive as purple flowers. They are nothing short of fancy because they indicate your plant is set to produce fruits! Some 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 bad light and high-temperature levels. Insufficient pollination and the wrong type of fertilizer could also be culprits.

Suppose your plant is not receiving sufficient light. This may cause nonproduction of fruits as plants generally require six to eight hours of sunlight to yield flowers and fruits. Consider moving them to a space where they can get adequate sunlight to encourage fruit production. If it experiences elevated temperature levels, this may also lead to the nonproduction of fruits. While they thrive in hot climates, too much heat can interfere with pollination. Watch out for this amid dry spells.

To counter this, make sure to keep them hydrated.

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

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

tomato fertilizer

Holes in the leaves

Leaves with holes are never a good sign of a plant’s health status. One cause of holes in your leaves is insects. Cutworms and slugs are just common garden pests you need to watch if you are cultivating tomatoes.

During winter, flea beetles typically hide underneath the leaflets and come out to feed on those leaves in spring. It results in 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 them. These nocturnal pests feed by creating oddly shaped holes. One way to determine whether a slug is your suspect is by looking for slimy tracks on the leaves and the ground.

If you notice the stems are being chewed within at least one inch of their base, then the culprit must be cutworms. These pests love to feed on buds, stems, and foliage. They measure up to two inches in length.

Earwigs are also notorious 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 them?

tomatoes on the vine

Like any other organism, tomatoes need water to thrive. However, it is not enough to water whenever and however you like it. Watering it too much or too little could cause problems mentioned in this article. These include:

  • Root rot
  • Low fruit production
  • Stunted growth
  • and brown leaves.

When they have the right amount of water to absorb nutrients, they grow healthily. Water passes through the root system, all the way to its stem and the leaves and flowers. But watering routines may vary depending on the type. It is important to water them deeply and gradually. It allows 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 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. There is no black and white rule on how often you should water them. One factor to consider is the weather. If it is too hot, you may consider giving them water once every three days. You also have to watch other signs such as wilting and dry soil.

However, these are not guaranteed indicators of immediate need for water. They may droop in the middle of the day, but they will return to normal at sunset. If it remains bent after sunset, this may signify parched ground. It is best to water 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 if you don’t want to be using a watering can. The latter is highly recommended if you plan to be away for weeks, allowing you to set a schedule.

A drip irrigation system also offers a more efficient way of distributing water. It allows the soil to absorb the water gradually. Installing your drip irrigation system is not as easy as setting up your fuel transfer tank at home. You will save a lot on time and water once it is in place!

FAQ

Should I remove yellow leaves from the tomato plant?

Once the tomato plants reach a height of around 15 inches, you’re likely to find yellow leaves or foliage. If these leaves are below the first set of flowers, you should remove them. But it’s advised to do nothing if they’re above the first set of flowers.

What are the signs of overwatering tomato plants?

Just as not giving enough water to plants can be harmful, overwatering is also damaging to their growth. There are sure signs you need to look out for in case of overwatering, including cracked tomatoes or bumps on the lower side of the leaf. As the overwatering continues, the roots begin to die. This causes the plant to wilt until the entire plant sags.

How do you fix yellow leaves on tomato plants?

Yellowing leaves on a tomato plant indicate a deficiency of magnesium. To permanently treat the problem, you need to increase the magnesium supply to the plant. You can either introduce fertilizers rich in magnesium or use a homemade Epsom salt mixture.

How to care for tomato plants

  1. Provide support to the plant.

    Using a cage or a stake, you can support the tomato vine. The stake ensures the tomato plant grows upward at a steady speed and remains unaffected by wind or rain.

  2. Regularly water the plant.

    Water the tomato plant every day with warm water at about 16 ounces. Make sure to aim the water at the roots instead of sprinkling from the top. As the plant grows, the water requirement increases. So make sure to increase the water supply gradually. The soil beneath the tomato plant should be wet but not completely soaked.

  3. Surround with mulch.

    At most, after two weeks, you need to incorporate a layer of mulch around the tomato plant. The mulch ensures moisture in the soil and controls weed growth.

  4. Provide additional nutrients.

    If your soil is rich in organic matter, you don’t need to worry about the nutrient supply. But if you’re concerned about the growth, choose a fertilizer that matches your nutrient requirement. Do not apply too much fertilizer as that could lead to overgrowth or disease.