Why Are My Tomato Leaves Curling?

Growing tomatoes is the pride and joy of many gardeners, but along the journey, you’re likely to meet with a few challenges. One of the most common problems people experience with their tomato leaves is curling. What causes this behavior, and what should you do about it?

Tomato leaves often curl due to improper watering habits, excessive heat, and an overabundance of nitrogen. If you overstress your plant by pruning it too much or have just recently transplanted it, you may also experience tomato leaf curling.

Published: November 8, 2022.

There are a number of causes that can leave you frustrated, wondering why your tomato leaves are curling, but thankfully, most of these causes can be remedied quickly.

The rest of this article will walk through the most common causes of tomato leaf curling and how to fix each one.

What Causes Tomato Leaves to Curl?

Curling leaves in plants are often caused by a number of factors. The most common among them are poor watering habits, improper nutrient balance, disease, environmental factors, and stress.

In general, the main cause of tomato leaf curl is stress, whether it’s stress from disease, over-pruning, or transplanting, tomatoes can be quite delicate. With their root systems in particular, sudden changes to their environment can cause problems that will harm your plants in the long run.

Watering Problems

Just about every gardener struggles with proper watering, and it’s not hard to see why. A number of environmental factors contribute to the amount of water your plants need, as well as the requirements of the plant itself, of course.

As such, it’s hard for most green thumbs to balance how much water a tomato plant needs. Both over and underwatering your plant can cause stress, especially for the picky tomato plant.

Underwatering your plant can starve it of essential nutrients, while overwatering can damage the root system, potentially leading to the dreaded root rot.

When it boils down to it, the curling of the leaves is the least of your worries if you’ve had a longstanding watering problem. Your leaves receding inward is a good sign, however, that your plant is unhappy and stressed.

Overwatering isn’t as likely to cause curling since there are a number of other symptoms—yellowing of the leaves, for one—that will present themselves before curling happens.

On the other hand, if the only symptom you’re seeing is curling, then underwatering is the most likely cause.

If the soil isn’t watered regularly, the tomato plant roots can’t transport it to the plant cells that serve the purpose of straightening the plant. As such, it loses its shape and starts to curl inwards to reduce water loss from sun exposure.

As a general rule, provide your tomato plant 2” of water every 2-3 days in a steady, slow stream and pour the water directly into the soil.

When watering the tomatoes, it is important to keep the leaves and the rest of the plant as dry as possible - cold(er) water can cause additional shock to the plants and can even lead to the development of some diseases.

It’s important to recognize that general advice for plants is helpful, but it’s up to you as the caretaker of your own garden to assess, based on environmental factors, whether your plants need more or less water.

Overheating

Speaking of underwatering, another problem that often goes hand in hand is overheating. You probably know that tomatoes are sun-loving plants that appreciate a lot of direct sunlight.

The issue is that when summer rolls around and temperatures stay above 85 degrees Fahrenheit for an extended period, tomato plants struggle. This issue becomes even more prevalent when the plants are already underwatered, creating an environment of heat stress and a lack of water.

In hotter weather, the plant loses more water in the process of transferring it to the leaves, resulting in the plant activating its aforementioned defense mechanism: tucking the leaves away to reduce heat loss through the leaves.

To protect your plants from this detrimental condition, you can install shade cloths designed to protect your plant during the hottest parts of the day, still allowing them to reap the benefits from the morning and evening rays. Of course, if you have potted tomatoes, then you can just move them elsewhere to a location that’s shaded during the warmest parts of the day.

Over-pruning

Pruning is one of those gardening habits that some people practice and others don’t. Regardless of where you fall on the pruning spectrum, it is important to note that over-pruning is never good for your tomato plant.

If you want to prune occasionally to make sure the leaves are off the ground, then you’re certainly able to do so to reduce the risk of soilborne diseases; however, don’t overdo it.

Pruning stresses the plant, and when combined with a range of other factors, it can certainly cause your plant to curl up because of stress.

If your plant is currently recovering from a pruning session, then don’t mess with it any further. It’s already in a state of distress and needs a little time to recover. Without any intervention, the plant will recover and be able to thrive within a few weeks.

Transplant Shock

Another very common cause of leaf curling is transplant shock. If you’ve recently transplanted your tomato plant, then you shouldn’t be surprised to see a little curling or yellowing of the leaves. These reactions are natural for plants that have experienced something stressful and aren’t any cause for alarm.

During this recovery period after a transplant, tomato plants are more susceptible to heat stress and diseases, so make sure that conditions are ideal for them so that they recover from the move without any incident! A couple of weeks should sort your nervous tomato plants right out.

Diseases

There’s no need to panic and immediately assume that your tomato plants have a disease. More often than not, the root cause can be traced back to some other form of stress, like a transplant or heat stress.

While these are much more common, there are some diseases that can cause leaf curls in your plant. One such disease is tomato yellow leaf curl virus—a rather creative name, don’t you think?

As the name suggests, the leaves curl and will pale or yellow along the edges. You can often spot the difference between the two by the way the leaves are upturned. If the leaves form a U shape, you might have something to worry about on your hands.

This disease is commonly spread by whiteflies, a common garden pest.

Tomato mosaic virus has a similar effect, causing the leaves to roll inward on themselves, but in addition to the yellowing of the leaves, you’ll also notice telltale spotted coloring and browning on the inside of the fruit.

These two conditions are quite alarming and can spread quickly to your other plants. Depending on the severity of the condition, you may need to take the affected plant and destroy it to prevent spreading to your other plants. Do not compost any diseased plants, and be sure to remove and replace any affected soil as well.

Too Much Nitrogen

Tomatoes love nitrogen and when the nitrogen is present in abundance, tomatoes will grow tall, with plenty of leaves that have tendency to become very green, leathery and - rolled.

Also, such plants are prone to pests and diseases - they are big, but weak.

To prevent leaves curling, it is important to keep the nitrogen in moderation, especially when the plant is flowering and bearing fruits.

For small gardens this means that the use of organic fertilizers is almost mandatory - they provide tomato plants with balanced amount of nutrients and improve the quality of the soil.

Herbicide

Another potential cause of curling that you need to keep an eye out for is herbicide use. Tomato plants are particularly susceptible to certain herbicides, particularly 2, 4-D, and dicamba.

You can often tell the difference between stress-based leaf curl and leaf curl caused by herbicides simply by observing how the plant appears. Plants that come into contact with herbicides tend to curl downwards and twist away down onto the stem. Newer leaves will exhibit these behaviors soon.

This problem isn’t common, but if your garden is close to crops that are going to be sprayed with herbicide, there’s not much you’re able to do. There are no anti-herbicide products out there to help you counteract the effects of herbicide spraying.

The best you can do is hope that the affected areas of your plant survive and that new growths are unaffected, although in many cases, you can expect your yield to be impacted by herbicide use.

If you’re using herbicides to protect your garden, it’s probably not a wise idea to continue doing so. Consider creating a healthier biodiverse garden environment where natural predators can roam.

Wasps, spiders, and ladybugs are all your friends when it comes to handling pests, and if you fertilize and aerate your soil regularly, you should be able to create a nutrient-rich, pest-minimal garden landscape that benefits all your plants.

It’s not always the simplest solution, but when it comes to herbicides, the damage to your plants can often be irreversible, prompting the need to discard your plant entirely.

Final Thoughts

There are a number of things that can detrimentally affect your tomato plant and cause its leaves to curl and even turn yellow.

Frequently, it’s not something you need to stress out about. More often than not, it’s an underwatering problem, a heat stress problem, or a combination of the two.

Protecting your plant from the sun in 85F+ temperatures and ensuring your plant gets enough water is a good starting place to keep your tomato plants healthy for the long run.