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Why Do Tomato Leaves Curl – and What To Do About It

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Why do tomato leaves curl? It doesn’t make sense. A healthy tomato plant’s leaves spread out to absorb as much light as possible. The sun’s energy combines with water and carbon dioxide in the leaves’ cells to produce food for the plant.

But curled leaves limit the amount of light the plant can soak in. That in turn curbs the plant’s energy production. Clearly, leaf roll is not good for a plant is working to produce fruit.

Your tomato plant most often curls its leaves for one simple reason: stress.

The plant is turning in on itself as a defense. Plants are trying to protect themselves. Leaf curl is but a symptom of a bigger issue. When a plant’s leaves twist or turn, all is not right in their world. Your plant is shouting, “Study me! I need help.”

Those twisty, rolled leaves can be caused by many factors. With a little bit of detective work, you can uncover why a tomato plant’s leaves curl and then take steps to help fix the problem. How do the leaves curl – upward? Or do they droop and curl? Is only part of the plant affected? Does the curl start at the topmost leaves or at the plant base?

Use this checklist to help you discover what’s making your tomato plant’s leaves twist and turn. Then you can take steps to fix the problem and help your plant to return to health.

Why do tomato leaves curl? Examine these 10 causes

1. Lack of moisture

Tomatoes are heat lovers. But even tomato plants buck with too much of a good thing. Heat can mean a lack of moisture which stresses tomato plants. Leaves are not able to take up enough water to regulate their exposure to high temperatures and excess sun. They respond by tightly rolling or curling up at the edges to conserve water, starting with the lower leaves first.

What to do

• Establish a consistent watering schedule for your plant, making sure tomatoes receive 1-3 inches of water a week (including rainfall).
• Mulch tomato plants to retain moisture.
• Offer shade to tomato plants during the heat of the day (10 AM – 2 PM)

2. Excess moisture

As you study your tomato plant, you may notice that its leaves are getting thick and turn inward and upward – particularly on older leaves at the top of the plant. Some foliage may overlap with each other. At first glance you may think, “Wow, this plant is healthy! Look at all the growth.” But think again. Has the plant hit pause on blossoming and fruiting? Have you had wet, cool weather? Or have plants received inconsistent watering?

The leaves’ inward twists are letting you know that the plant is getting too much water. Half to three-quarters of a plant’s leaves can be affected. But there’s good news: tomato plants can outgrow leaf roll from excess moisture and produce healthy fruit.

What to do

• Plant tomatoes in well-drained soil.
• Reduce watering during raining periods.
• Water only at the base of the plant.
• Watch your plants to make sure curled leaves are not the result of another issue.

3. Transplant shock

Young tomato plants lack strong root systems. As you plant seedlings in the garden, they experience stress – particularly because they lack water or are exposed to excessive wind and sun. That makes them more vulnerable to diseases, pests, and conditions. One symptom of transplant shock is drooping, curling leaves.

What to do

• Allow tomato seedlings to harden off before moving them to their permanent home.
• Avoid transplanting tomatoes when the weather is hot and sunny. Choose an overcast day to reduce stress.
• Give new tomato transplants shade for 7-14 days to help them acclimate to the garden or container.
• Water regularly.

4. Over pruning

Leaves are a plant’s energy factories. Remove too many at once and the tomato plant can be stressed. Its response may be to curl its leaves to protect the plant from further pruning. If leaves on your tomato plant curl after a trim, then over pruning may be the culprit – particularly if you gave your tomato plant its haircut in hot weather.

That’s not to say you shouldn’t prune your tomato plant – quite the contrary. Pruning can enhance production and produce more tomatoes, bigger tomatoes, and more flavorful tomatoes. 

What to do

• Avoid pruning during hot temperatures or during a drought.
• Don’t over prune. Trim some and wait to allow your plant to respond.
• Water the plant and give it time to recover. If you’re in a heat wave, provide shade during the hottest parts of the day.

5. Herbicide drift

Lawn weed killers often contain broad-spectrum herbicides such as glyphosate and growth regulators 2,4-D and dicamba. If you spray your lawn – or a neighbor does so – then herbicides may drift onto your tomato plants.

An herbicide-related leaf curl looks different than one caused by environmental conditions. Rather than rolling tightly to protect themselves from water loss, drifting weed control products and treated grass clippings can make tomato leaves curl downward and become stunted, as if trying to avoid the drift overhead.

Most of the time herbicide damage is not fatal. If you stop applying herbicides, soon your plant will recover and re-strengthen.

What to do

• Avoid using herbicides near your tomato patch.
• If you must spray, do so on a day with no breeze.
• Ask your neighbors to pray their yards on days when wind is low or still.

6. Herbicide residue

Your tomato plants may be exposed to herbicide residue in compost or mulch. It’s not uncommon for pasture herbicides (picloram, clopyralid, or aminopyralid) to remain in soil products for up to 18 months. Then as the affected compost or mulch is spread over the garden, it can impact tomatoes. You’ll face this challenge most often if you buy hay or soil product directly from a commercial pasture.

What to do

• Purchase compost and mulch from a quality source.
• Make your own compost.
• Use mulch from your own trees or purchase rolls of weed barrier.

7. Inappropriate nutrition

Nitrogen encourages leaf growth. It’s a key component in most garden fertilizers, including tomato fertilizers. And truth be told, tomato plants need large amounts of nitrogen when they first start the season so they can put out leaves to help with photosynthesis.

But as plants mature, they need good doses of phosphorus and potassium for flowering and fruiting. Too much nitrogen means too many leaves – which can mean not enough nutrients and water in the soil to sustain the over-leafed plant.

If your plant is getting too much nitrogen, it will show you that it is stressed and then work to protect itself by curling its leaves and drooping downward. On the other hand, inadequate potassium and phosphorus can stunt the plant. Its leaves will yellow and curl as a warning sign that it needs help.

What to do

• Test your garden soil before planting and add amendments accordingly.
• Add compost to the soil before planting tomatoes.
• Use a balanced tomato fertilizer ever 3-4 weeks (for garden tomatoes) and every 1-2 weeks (for container tomatoes).
• If plants get too leafy early in the season, prune appropriately.

8. Broad mites

Broad mites are microscopic pests. You cannot see them with the naked eye. But you can recognize their work in your plant’s stunted growth. Affected leaves have green veins (against browning edges). Newer growth droops, curls, or twists. Mature leaves turn up around the edges.

The perpetrator, also known as Polyphagotarsonemus latus, pierces the undersides of leaves to extract nutrients from plants. In the process, broad mites excrete toxins that causes leaves to curl, shrivel, wilt, or brown.

What to do

• Pinch off affected leaves.
• Treat plants with insecticidal soap or neem oil.
• Remove or mow weeds near tomato plants, which offer a home to broad mites.

9. Tomato spotted wilt virus (TSWV)

Your plant’s leaves curl. And they have a bronze coloring along with black spots, lines, or circles. Plus, the plant’s stems have streaks, growth is stunted, and the fruit is distorted. All those factors combined can indicate the tomato spotted wilt virus (TSWV) has invaded your tomato plant’s space.

TSWV is caused by a virus, rather than a fungus or bacteria. It’s spread by thrips (Thysanoptera: Thripidae), which are small flying insects that contract the virus as larvae and transmit it to plants as adults, when they’re feeding. Thrips prick the leaves, suck the contents, and transfer the virus in the process. There’s no effective treatment for TSWV, but you can take steps to minimize its impact.

What to do

• Control weeds volunteer plants in and around your garden so thrips have no home. Clean up debris.
• Control active thrips. Set out sticky traps. Treat tomato plants with insecticidal soaps or organic botanical insecticide (pyrethrin.)
• Plant disease-resistant varieties, noted with “TSWV” listed after the variety name on its label.

10. Curly top virus (CTV)

Two pests spread a nasty disease known as curly top virus (CTV): the beet leafhopper and white flies. Young plants are particularly susceptible. And CTV spreads particularly quickly in humid weather.

When tomato leaves are curled, puckered, yellowing, and twist upward, take a closer look at the plant. If the plant looks as if it’s wilting, then water it. If the plant doesn’t revive, then there’s a good chance it may have fallen victim to CTV.

What to do

• There’s no effective treatment for curly top virus.
• Remove and destroy affected plants.
• Take steps to control the beet leafhopper and white flies by removing weeds and debris. Reduce opportunities for the pests to overwinter in overgrowth.

Why do tomato leaves curl instead of wilt?

A special note: curling leaves are different than tomato wilt. When one of the five kinds of tomato wilt attack your plant, then the stem, fruit, and leaves are affected. But when just the foliage falls victim, look beyond tomato wilt. https://www.tomatodirt.com/identifying-tomato-plant-diseases.html

Look at the way the leaves are twisting. Search for other symptoms, too. And with a bit of observation you’ll soon find the root cause for your curling tomato leaves and then be able to apply a solution.

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