8+ Simple Remedies for Yellow Leaves on Tomato Plants

Are some of your tomato plant leaves turning yellow? There are numerous potential reasons for tomato leaves turning yellow. This post covers some of the most common causes of yellow leaves on tomato plants, how to resolve the problem, and ways to prevent these issues in the future.

While tomatoes are usually easy to care for, it’s critical to monitor your plants for signs of distress. Some discoloration of older leaves toward the plant’s bottom is normal. However, take action right away if the new growth or entire plant looks affected. Yellowing tomato leaves can come from a bacterial or fungal disease, pest damage, or an environmental cause related to soil culture or nutrient and water levels.

Whatever the cause, rest assured that there is usually a straightforward solution for the problem, as long as you catch it early enough. Prevention is the best pest and disease management approach. Always clean your gardening tools between each use and keep your plants’ leaves dry when watering.

Why are the Leaves on My Tomato Plant Turning Yellow?

Yellowing leaves can indicate various conditions. As such, start by examining all possible causes to determine the problem’s most likely source. Sometimes all you need to do is adjust your watering schedule or give the plant some extra fertilizer. In other cases, more in-depth treatment methods are necessary.

Proper plant care requires us to learn their “language.” Plants rarely exhibit a single isolated symptom, so take note of other irregularities in your tomato plant’s performance and appearance. Are the leaves curling or wilting? Is the plant dropping a significant amount of leaves or flower buds? Have you noticed recent damage to the leaves or stems?

Yellow leaves are one of the most noticeable signals of plant problems. But to determine the underlying cause and find a remedy, look for other clues that will help narrow down the list of possibilities.

Environmental Factors that Lead to Yellow Leaves on Tomato Plants

Some of the simplest tomato plant problems to fix are the plant’s growing conditions. Chlorosis is the scientific term for yellowing tomato leaves caused by diminished chlorophyll production.

Possible causes for plants not making enough chlorophyll include poor water drainage, nutrient deficiencies, high soil alkalinity, and damaged or compacted roots. Find out more about chlorosis causes and remedies in this article from the Morton Arboretum.

Watering

Incorrect watering is one of the most frequent reasons for tomato leaves turning yellow. Overwatering and underwatering can both result in yellow tomato plant leaves.

When garden soil stays too wet, plants’ roots suffocate and rot because they can’t get enough oxygen. As a result, they cannot deliver sufficient nutrients and water to the rest of the plant.

Without enough water, a root system cannot absorb the nutrients it needs from the soil. To survive dry conditions, plants must stop transpiration or water loss through the leaf surfaces. They will restrict the flow of chlorophyll and water and drop their leaves. The leaves typically turn yellow before falling off.

In most cases, it’s crucial to let the soil surface dry out a bit between watering. Test the soil moisture by inserting a finger up to the first knuckle. If some dirt sticks to your fingertip, wait a little longer before rewatering. If not, it’s time to water.

It’s best to water your plants as needed instead of on a strict schedule. Plants ingest water at different rates based on the current environmental conditions. Irrigate from the plant’s base and avoid splashing water on the leaves as much as possible. Protect your garden soil with a thick layer of mulch to retain moisture, suppress weeds, and prevent wind erosion.

Nutrient Deficiencies

If your tomato plants don’t get all of their required nutrients, the leaves start turning yellow. Observe the yellowing pattern to determine which nutrients are lacking in your garden soil.

Nitrogen deficiency brings about a general yellowing of the whole plant, beginning with the oldest leaves toward the plant’s bottom. If the problem continues, younger leaves also become affected.

Potassium deficiency causes the edges of tomato plant leaves to yellow, starting with the oldest ones. Imbalanced potassium levels in the soil also prevent plants from absorbing other nutrients. Too little potassium impedes iron intake. Too much prevents the plants from taking up calcium, magnesium, and nitrogen.

A shortage of magnesium produces yellowing between leaf veins on the oldest leaves. The yellowing appears first at the leaf’s center and moves outward.

If plants don’t have enough iron, the newest leaves toward the top of the plant and tips of the branches show yellowing between leaf veins. The discoloration begins at the edges and eventually turns the entire leaf pale yellow or white before it drops off of the plant.

Calcium deficiency creates several plant problems. Along with yellow or brown spots on the leaves, blossom end rot also comes from a lack of calcium. A watery brown patch forms on the fruit’s bottom where the flower was.

To ensure that your plants receive the proper nutrients, apply an organic, all-purpose fertilizer every four to six weeks throughout the growing season. In addition, mixing Epsom salts and organic compost into your garden beds in the springtime helps provide all of the micronutrients and minerals that plants require to flourish.

Soil pH Levels

Another vital aspect of soil health and plant nutrition is the pH level. Although some plants prefer acidic soil, most types of fruits and veggies grow best with a neutral soil pH.

In soil with a pH level that’s too low or too high, plants cannot absorb the available nutrients. If you have persistent problems with yellow leaves and other symptoms of plant distress, consider ordering a soil test to establish whether the pH or nutrient levels are imbalanced. Many soil test labs can also recommend the best soil amendments for bringing your garden back into balance.

This article from PlantSnap has more helpful information about plant nutrition if you’d like to learn more about how plants take up nutrients from the soil.

Plant Diseases that Cause Yellow Leaves on Tomato Plants

In general, tomatoes are incredibly easy to grow. However, they’re sometimes susceptible to various bacterial and fungal diseases. Yellowing leaves are often the first visible symptom of these plant diseases.

To minimize the risk of spreading plant diseases, utilize a soaker hose or drip irrigation to avoid splashing water on the leaves. Providing adequate air circulation is also critical for plant health. Leave at least a foot or two of space between tomato plants and prune them regularly to ensure sufficient airflow.

Crop rotation every few years is also beneficial. Pathogens can persist in the soil from year to year. Avoid growing the same type of plants in one area for more than two or three seasons.

Early Blight

Early blight is a fungal disease that results in irregular yellow patches on the lower leaves. These soon turn brown in the center, surrounded by a yellow halo. Left untreated, the leaves and stems shrivel up and fall off.

Immediately remove all infected leaves and branches at the first sign of disease. Thoroughly sterilize your tools, and don’t add the diseased plant matter to your compost.

Fungal spores spread through splashing water, so try to keep the leaves dry when watering and facilitate good airflow. Prune the bottom branches of your tomato plants so they don’t touch the ground.

Early blight comes from a soil-borne fungus. Avoid growing plants susceptible to the disease, like tomatoes, peppers, eggplants, and potatoes in that area for the next few years.

Early blight is treatable with an organic copper or sulfur fungicide spray if you catch it soon enough. Or, make a DIY fungicide spray to treat and prevent fungal plant disease.

DIY Fungicide Spray

• 1 gallon of water
• 1 tablespoon of baking soda
• 1 tablespoon of vegetable oil
• 1 teaspoon of mild dish soap

Mix all the ingredients in a clean spray bottle and shake to blend. Then, spray all surfaces of the plant every two or three days until the symptoms disappear. If you’ve had issues with early blight in the past, spray your tomato plants once each week as a preventative treatment.

Late Blight

True to its name, late blight is a fungal disease that often occurs late in the growing season. Although it’s normal for a few of the older leaves to turn yellow and fall off, it’s pretty apparent when it happens too much. Another sign of late blight is greyish-green, watery lesions that darken over time and form a white fungal growth on the leaves’ undersides.

Late blight thrives in warm, humid conditions. Spores spread via wind and splashing water. First, remove all infected leaves when you first spot signs of disease.

Be sure to provide adequate spacing between your tomato plants for air circulation. Also, sterilize your garden tools after each use to avoid accidentally spreading disease to other plants.

Treat plants infected with late blight using organic fungicide. Reapply every few days until you stop seeing new yellow spots.

Septoria Leaf Spot

Septoria leaf spot, resulting from the fungus Septoria lycopersici, spreads quickly in wet, humid environments. The initial symptoms appear similar to early blight, with yellow spots on the lower leaves that turn brown and spread. Left untreated, the spots converge and destroy the entire leaf.

Treat Septoria leaf spot with an organic fungicide. Copper or sodium bicarbonate-based products work well.

Remove any diseased plant matter from your garden at the end of the season, and dispose of it in the garbage rather than composting it. Fungal spores often persist in decaying plant matter and may cause more problems the following year.

Verticillium Wilt

Verticillium wilt is another soil-borne fungus. It causes yellowing from the central leaf veins, and the pattern moves outwards in a V-shape. This plant disease progresses slowly but will ultimately kill the plant. Unfortunately, there is no known treatment.

If you suspect verticillium wilt, scrape away a tiny area near the base of the tomato plant’s main stem. The fungus is likely present if the plant tissue is brown rather than white. Pull up the entire plant and dispose of it off of your property.

Verticillium fungi persist in the soil for several years. Select disease-resistant tomato varieties and rotate where you plant tomatoes in your garden.

Fusarium Wilt

Fusarium wilt tends to develop as the fruit begins maturing. The lower leaves turn yellow first, and sometimes only one branch shows symptoms.

Fusarium wilt also comes from a soil-borne fungus and has no known cure. Follow the same program as for verticillium wilt – remove the infected plant, look for disease-resistant tomato cultivars, and practice crop rotation.

Pest Attacks Can Generate Yellow Leaves on Tomato Plants

Tomato plants frequently get targeted by various insect pests like aphids, spider mites, whiteflies, tomato hornworms, and more. Tissue damage from insects’ feeding activity may turn the leaves yellow and stunted.

To eliminate an infestation of small, soft-bodied insects like aphids, mites, thrips, or whiteflies, spray all plant surfaces with an organic pesticide like insecticidal soap, horticultural oil, or neem oil. Also, get the leaves’ undersides, as that’s a favorite hiding spot.

Organic insecticides like spinosad or Bacillus thuringiensis (Bt) kill tomato hornworms. However, spraying insecticides also kills beneficial garden insects like pollinators and predators. Use cultural controls like companion planting, floating row covers, and natural repellants to control pest populations whenever possible.

Strong odors like chili pepper and garlic repel hornworms. If you’re dealing with a severe infestation, make this DIY tomato hornworm repellent spray.

Homemade Tomato Hornworm Repellent

• 3 heads of garlic
• 2 tablespoons of cayenne powder or 6 fresh hot chili peppers
• 7 cups of water
• 1 tablespoon of vegetable oil
• 1 teaspoon of liquid dish soap

Place the ingredients in a food processor or blender and liquify them. Pour the mixture into a clean spray bottle through a strainer to catch any garlic or pepper pieces. Or, let it steep for a day or two for extra potency. This spray also deters other pests like aphids, spider mites, slugs, deer, and rodents.

Learning how to interpret your tomato plants’ signs of distress can be challenging. Yellowing leaves indicate numerous different problems. When you see tomato plant leaves turning yellow, take note of the pattern, size, and shape of yellowing tomato leaves to help determine the possible causes and an effective remedy. But rest assured that there’s a straightforward solution to most tomato plant problems.

Do you have any questions or suggestions about tomato leaves turning yellow? Feel free to share them in the comments! If you found these tomato plant care tips useful, please share this post about yellow leaves on tomato plants with your fellow gardeners.