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If you’re a tomato grower, you may have experienced any number of frustrating issues on tomato leaves, one of those being leaf curling. This is a condition where the leaves of a tomato plant curl inward or upward, making them look distorted. Let’s explore what causes leaf curl on tomato plants and how to prevent or treat it.

What causes leaf curl on tomato plants

There are quite a few reasons why you may be seeing curl on your tomato plant leaves. These range from environmental conditions, such as disease in the soil or herbicide drift, to viral infections that could then spread to the rest of your tomato plants. Being able to pinpoint the cause of your tomato’s leaf curl will help you to eliminate it in the future and hopefully to stop a spread before it overtakes everything. 

This article has the causes of leaf curl broken down by environmental factors, pests and diseases, nutritional deficiencies, and herbicide residue that may lead to leaf curl in tomato plants. Let’s figure out what may be going on with your plant growth and the curling leaves you’re seeing. 

Environmental Stress and Leaf Curl

As with all plants growing in the garden, environmental factors can play a big role during the growing season and environmental stress can be a significant factor that causes leaf curl on tomato plants. When exposed to high temperatures, low humidity, or insufficient watering, your tomato plant curls its leaves to conserve moisture.

• High temperatures are a common environmental stressor that can cause leaf curl in tomato plants. If the temperature is too hot, the plant can lose too much water through transpiration, causing the leaves to curl inwards. Low humidity exacerbates the problem, making it harder for the plant to retain moisture.
• Insufficient watering can also lead to this leaf curling condition. When your tomato plant doesn’t receive enough water, it can’t take up the nutrients it needs from the soil. This can cause the leaves to curl up as the plant tries to conserve water also known as physiological leaf curl.
• Extreme weather conditions like heavy rain or strong winds can also cause environmental stress and lead to leaf curl. Heavy rain may cause soil compaction and waterlogging, depriving the roots of oxygen and causing stress. Moreover, strong winds inflict wind damage to the plant and disrupt its ability to take up water and nutrients.

Protecting your tomato plant from environmental stressors

To prevent environmental stress from causing this condition in your tomato plants, it’s important to take some precautions. 

• Choose a location for your plants that offers good air circulation and partial shade if you live in an area of high temps and low humidity. Tomatoes clearly love the heat and sun, but a combination of extreme temps and dry conditions can take its toll.
• Make sure to keep the soil consistently moist but not waterlogged. Excessive moisture can lead to root rot. Deep watering a few times a week will help your tomato plant to take up nutrients effectively and avoid stress. Using a good quality mulch around your plants will help to keep the moisture from evaporating from the soil as quickly, and it reduces how often you’ll have to water. 
• It’s also important to avoid watering your plants during the hottest part of the day, as this can cause the water to evaporate before the plant can absorb it. Instead, water your plants in the early morning or late afternoon when the temperature is cooler. 
• Water tomato plants deeply twice a week instead of a daily watering. Also water them as close to the base of the plant as you can to avoid wetting the leaves. Obviously, rain wets the entire plant, but for efficient watering, try to keep the water at the base. 
• During hot, dry weather, you can cover your plants with shade cloth to protect them from harsh sunlight and heat. This can also reduce the impact of environmental stressors like high temperatures and low humidity. 

By taking these simple steps, you can prevent these environmental stressors in your tomato plants and help to ensure a healthy harvest.

Pests and Diseases that cause Leaf Curl

If watering wasn’t enough, there are also tomato pests and diseases that can also cause leaf curl on tomato plants. Insect damage from the moisture being sucked out of the leaves will cause them to curl. Some common culprits include:

• Aphids– these soft bodies sucking insects are tiny and usually come in large numbers. They are fairly easily dealt with though and you can see my full article on How to Get Rid of Aphids here. 
• Whiteflies– You’ll know you have white flies if you see tiny white flies scatter when you move the leaves of your tomato plant. These pests are annoying, but not impossible to deal with. They feed on the leaves which in turn causes the leaf to curl. See this article from The University of California for more information. 
• Spider mites– Much like aphids and whiteflies, spider mites will suck the moisture out of the leaves of the tomato plant, causing them to curl. They seem prevalent during hot and dry conditions. See this article from The University of Florida for info on how to combat them in your garden. 

Diseases and tomato viruses that cause tomato leaf curl are 

• Tomato yellow leaf curl virus (TYLCV). These can damage the leaves of your tomato plant, causing them to distort and this can happen due to the silverleaf whitefly infecting your plants. This is a good incentive to try to take care of whiteflies. Here’s a great article on tomato yellow leaf curl virus for homeowners from the University of Florida. 
• Tomato Spotted Wilt Virus: Though this will affect more than just the leaves, infected plants will have leaves that curl and stunted growth of the entire plant itself. You may notice abnormal growth on tomato plants, and this is a good indication that there is an issue. For more on this particular virus, check out Oklahoma State’s page. 

Whether trying to keep pests or disease at bay, always keep your garden free of debris and clean to prevent pest infestations and diseases. Inspect your plants and fruit production regularly for signs of pests or diseases, and take action immediately if you notice any problems. You can also use natural remedies like insecticidal soap or neem oil to control pest populations. See my full post on 6 Tips for Natural Pest Control or my e-book Natural Pest Control for the Home Garden. 

Nutrient Deficiencies

Tomato plants need a variety of nutrients to grow healthy and strong, and they’re heavy feeders since it takes a lot of energy to produce tomatoes. If your plants are lacking in certain nutrients, they may curl their leaves as a way to conserve resources. Some common nutrient deficiencies that can cause this condition include:

• Nitrogen: Lack of nitrogen can cause the leaves to turn yellow and curl upward. A good all purpose organic fertilizer such as Espoma is good for this. Do be cautious to not to use too much nitrogen though, as this will give you big bushy plants with very little fruit productions. 
• Potassium: Lack of potassium can cause the edges of the leaves to curl and become brown almost as if they have been burned. There will also be limited fruit growth. 
• Magnesium: Lack of magnesium can cause the leaves to curl upward and develop yellow spots. The most common fix for magnesium deficiency is to use epsom salts, though you certainly want to do so after reading this article from South Dakota State University. Epsom salts are used for many garden applications, so you just want to make sure a magnesium deficiency is really what you’re dealing with before using them. 

To prevent nutrient deficiencies, fertilize your tomato plants regularly with a balanced fertilizer such as Espoma’s Garden Tone, and once your plants begin blooming, switch to Tomato Tone which has less nitrogen. 

Herbicide Damage: A Potential Cause of Leaf Curl on Tomato Plants

Herbicide damage is another common problem that can be the potential cause of leaf curl on tomato plants. If you’ve used herbicides or weed killers in your garden, follow the manufacturer’s instructions carefully and avoid using them near your tomato plants.

If you suspect herbicide damage, either from use in your own yard or that the wind has brought over from a neighbor’s, I’m afraid that there isn’t much you can do to fix the problem. Your best bet is to remove the affected plants and start fresh. 

Other Tomato Growing Problems That Can Cause Leaf Curl

Leaf curl can also be caused by other tomato-growing problems, such as:

• Overcrowding: If your plants are too close together, they may compete for nutrients and water, leading to leaf curl.
• Root damage: Damage to the roots of the plants can also cause leaf curl. Make sure to handle your plants gently and avoid damaging the roots when transplanting.
• Improper pH: Tomato plants prefer a slightly acidic soil pH of around 6.0 to 6.8. If your soil pH is too high or too low, your plants may experience leaf curl and other problems.
• Fungal infections: Fungal infections, such as verticillium or fusarium wilt, can cause leaf curl in tomato plants. To prevent fungal infections, the best thing you can do is to plant disease-resistant varieties; many seed catalogs will have tomato varieties labeled that are wilt resistant. (See my Favorite Garden Seed Companies that carry wonderful tomato varieties.)

Should You Remove the Leaves with Leaf Curl?

One question that many tomato growers have is whether they should remove the leaves with leaf curl from their plants. The answer depends on the severity and the cause of the problem.

• If a temporary problem causes the leaf to curl, the affected ones may recover on their own over time. In this case, you may choose to leave the leaves in place and monitor the plant to see if the problem resolves itself.
• However, if the leaf curl is caused by a more serious problem, such as a fungal infection or viral disease, it may be best to remove all those that are affected. This can stop the disease from spreading to other parts of the plant and can improve overall plant health. Do not put affected plants into the compost pile. Instead, throw them in the trash to prevent the spread of any disease or virus. 

When it comes to removing these leaves, make sure to use clean, sharp tools to avoid damaging the plant. Dispose of them in the trash to prevent the spread of disease, and be sure to clean whatever tools were used to remove the leaves or parts of the tomato plant. 

Did you find this helpful? Then don’t forget to explore my other articles on tomato plant issues! I include even more information on cultivating healthy, thriving tomato plants. And if you have insight from growing tomatoes that you’d like to share, feel free to comment below. Gardeners are always learning from each other!