Have you noticed your tomato plant leaves turning yellow? Although tomatoes are generally easy to care for, it’s essential to closely monitor your plants for any signs of distress. In this article, you’ll learn about the most common causes of yellow leaves on tomato plants, how to remedy the problem, and how to prevent future issues in your garden.
There are numerous reasons for yellow leaves on tomato plants. While some yellowing of older leaves is normal, take action quickly if the new growth or entire plant becomes affected.
Yellowing tomato leaves might result from bacterial or fungal disease, attacks from pests, or an environmental cause related to water levels or soil culture. Whatever the cause, there is usually a straightforward remedy for the problem, as long as you start addressing it early enough.
- Why are the Leaves on Your Tomato Plant Turning Yellow?
- Growing Conditions that Lead to Tomato Plant Leaves Turning Yellow
- Plant Diseases that Cause Yellowing Tomato Leaves
- Pest Attacks Induce Yellow Leaves on Tomato Plants
Why are the Leaves on Your Tomato Plant Turning Yellow?
Because yellowing leaves may indicate a wide variety of conditions that cause plant distress, it’s necessary to examine all possible causes and determine the most likely source of the problem, whether you grow indoor tomato plants or have them outside.
Sometimes all that’s required is adjusting your watering schedule or giving the plant some extra fertilizer. In other cases, the issue calls for more in-depth methods.
Remember that prevention is the best treatment, so ensure that you regularly clean your gardening tools between uses and try to minimize the amount of water that splashes on your plants’ leaves.
Plant care requires us to learn their language. It’s rare for plants to exhibit one isolated symptom, so note other differences in your tomato plant’s appearance.
Are the leaves wilting or curling? Is the plant dropping its leaves or flower buds? Have you noticed damage to the leaves or stems?
Yellow leaves are one of the most obvious signs of plant problems. To determine the underlying cause, look for other clues that help narrow down the list of possibilities.
Growing Conditions that Lead to Tomato Plant Leaves Turning Yellow
One of the easiest tomato plant problems to fix is the plant’s growing conditions. The scientific term for yellowing tomato leaves caused by a lack of chlorophyll is chlorosis.
The underlying causes may include poor water drainage, nutrient deficiencies, high soil alkalinity, and compacted or damaged roots.
The most common reason for tomato leaves turning yellow is improper watering. Both overwatering and underwatering result in yellow tomato plant leaves.
In soil that’s too wet, the plant’s roots suffocate and rot because they cannot absorb enough oxygen. As a result, they can’t deliver adequate amounts of water and nutrients to the rest of the plant.
When the root system doesn’t receive enough water, plants cannot absorb nutrients from the soil. To prevent water loss through transpiration, the plant restricts the flow of water and chlorophyll and drops its leaves.
Typically the leaves turn yellow before falling off. To prevent overwatering, allow the soil to dry out between watering. Test the soil by inserting your finger up to the first knuckle.
If dirt sticks to your finger, wait a bit longer before rewatering. If your finger is dry, it’s time to water. It’s best not to water on a strict schedule but rather on an as-needed basis. Plants consume water at different rates depending on the current conditions.
Water from the base of the plant and try to avoid splashing water on the leaves as much as possible. Apply a layer of mulch an inch or two thick around the plants to protect the soil from wind erosion and retain moisture.
If your tomato plants aren’t getting all of the nutrients they need, the leaves may turn yellow. It’s possible to determine which nutrients are lacking in your soil based on the yellowing pattern you observe.
Nitrogen deficiency causes a general yellowing of the entire plant, beginning with the older leaves toward the bottom of the plant. If the problem persists, younger leaves become affected as well.
Potassium deficiency turns the edges of tomato plant leaves yellow, beginning with the older leaves. Imbalanced potassium levels also inhibit plants’ ability to absorb other nutrients.
Too little potassium prevents plants from taking up iron in the soil, and too much inhibits the absorption of calcium, magnesium, and nitrogen.
A lack of magnesium leads to yellowing between leaf veins on older leaves. The yellowing typically starts at the leaf’s center and moves outward.
By contrast, if plants don’t receive enough iron, the newest leaves at the top of the plant and the branch tips exhibit yellowing between leaf veins.
Calcium deficiency generates several plant problems. In addition to yellow or brown spots on the leaves, a lack of calcium causes blossom end rot. The fruit develops a watery brown patch on the bottom where the flower was.
To assure that your plants receive the proper nutrients, fertilize every four to six weeks throughout the growing season. Adding Epsom salts to your garden beds in the spring helps provide all of the minerals and micronutrients that plants require to thrive.
If your soil pH is too low or too high, plants cannot absorb the nutrients in the soil. If you have a persistent problem with yellow leaves and other plant distress symptoms, consider doing a soil test to determine if pH or nutrient levels are imbalanced.
Most soil test labs also provide recommendations for the best soil amendments to bring your garden back in balance.
Plant Diseases that Cause Yellowing Tomato Leaves
Although tomatoes are generally easy to grow, they’re susceptible to various bacterial and fungal diseases. Often, yellowing leaves are the first symptom of these plant diseases.
To minimize the risk of a plant disease spreading through your garden, use drip irrigation to avoid splashing water on the plants’ leaves. Air circulation is another key factor for plant health.
Avoid planting crops too close together, and prune your tomatoes regularly to ensure proper airflow.
Crop rotation is also beneficial, as many pathogens persist in the soil from year to year. Refrain from growing the same type of plants in one garden area for more than two seasons in a row.
Early blight is a fungal disease signaled by irregular yellow patches on the lower leaves at first. These spots then turn brown, surrounded by a yellow halo. If left untreated, the leaves and stems turn yellow and shrivel up.
At the first sign of disease, remove all of the infected leaves and branches. Thoroughly wash your tools afterward, and don’t add the plant matter to your compost.
The fungus spreads through splashing water, so try to keep water off the leaves when irrigating and ensure that your plants get adequate airflow. Prune the bottom leaves of your tomato plants so they don’t touch the ground.
Treat early blight with an organic copper fungicide spray. Or, try making your own DIY fungicide spray to treat and prevent plant disease.
Put the ingredients in a clean spray bottle and shake vigorously to blend. Spray all parts of the plant, including the leaves’ undersides. Spray the plants every two or three days until the symptoms disappear.
Early blight comes from a soil-borne fungus. Avoid planting varieties susceptible to the disease, like tomatoes, peppers, eggplants, and potatoes in the same area for the next few years.
True to its name, late blight occurs late in the growing season. While it’s normal for some of the older bottom leaves to turn yellow and fall off at the end of summer, there are other signs to look for.
Identify late blight on tomato plant leaves by greyish-green, watery lesions that darken over time and form a white fungal growth on the leaves’ undersides.
This fungal disease thrives in warm, humid conditions and spreads by wind and splashing water. Remove infected leaves at the first sign of infection, and ensure that your tomato plants are adequately spaced apart for air circulation.
Clean your tools after use to avoid spreading the fungus to other plants. Treat the infected plants using the same methods as for early blight. Reapply the fungicide every few days until you stop noticing new yellow spots.
Septoria Leaf Spot
Septoria leaf spot, produced by the fungus Septoria lycopersici, thrives in wet, humid conditions. The initial symptoms are similar to early blight, with yellow spots on the lower leaves that eventually turn to brown tomato leaves and begin spreading.
If left unchecked, the brown spots converge and kill the entire leaf. Use the same treatment methods as for early blight.
Make sure to remove all of the diseased plant matter from your garden at the end of the season, and dispose of it in the garbage instead of composting it. The fungal spores may persist in the plant matter and cause problems with tomato plants again the following year.
Another soil-borne fungus, verticillium wilt appears with yellowing from the middle leaf veins, moving outwards in a V-shape. This plant disease is slow to progress but eventually kills the plant. Unfortunately, there is no effective treatment.
If you suspect your tomato plants have verticillium wilt, scrape a small area at the base of the main stem. If the tissue is brown instead of white, the fungus is present.
Remove the entire plant and dispose of it in the garbage. The fungus persists in the soil for several years, so look for tomato varieties resistant to verticillium wilt and rotate where you plant your tomatoes annually.
Fusarium wilt often develops as the fruit begins to mature. It affects the lower leaves first and sometimes only appears on one branch of the tomato plant. It’s also the result of a soil-borne fungus and has no cure.
Follow the same procedures as for verticillium wilt. Remove the infected plant, practice crop rotation, and look for disease-resistant varieties.
Pest Attacks Induce Yellow Leaves on Tomato Plants
Tomato plants are frequently targeted by a wide variety of insect pests like aphids, whiteflies, spider mites, tomato hornworms, and more. The tissue damage from insects’ feeding activity may cause leaves to turn yellow and stunted.
Learn what to spray on tomato plants to keep bugs away. To combat an infestation of small, soft-bodied insects like aphids, thrips, mites, or whiteflies, spray all parts of the plant with insecticidal soap or horticultural oil. You can also spray neem oil on tomato plants without harming the fruit.
Take extra care to cover the leaves’ undersides, a favorite hiding spot for small insects and aphids on tomato seedlings or mature plants.
Larger pests like tomato hornworms must be picked off by hand. Strong odors like garlic and chili pepper repel hornworms. If you have a severe infestation, try making a homemade tomato hornworm repellent spray using this recipe.
Combine the ingredients in a blender and mix until liquified. Pour the mixture into a clean spray bottle using a strainer to catch any pepper pieces or garlic pieces.
Or, allow it to steep for a day or two for a stronger scent. This spray also effectively repels other pests like aphids, slugs, spider mites, deer, and rodents.
Learning to interpret your tomato plants’ signs of distress is sometimes challenging. Yellowing leaves are a symptom of numerous afflictions.
When you notice your tomato plant leaves turning yellow, it’s essential to note the size, shape, and pattern of yellowing tomato leaves to determine the possible causes and how to remedy the problem. In most cases, there’s a straightforward solution.
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