Why Tomato Leaves Curl (Common Causes and How to Fix Them)

Ack! My tomato leaves are curling! Is my plant dying?

Healthy tomato plant leaves spread out to soak up the sunshine and heat. So what does it mean if the leaves are curling up? 

Not every curled leaf is a reason to panic. We’ll walk you through the causes of tomato leaves curling and what you can do about it. We’ll explain when it’s a temporary setback and when it’s time to remove the plant.

Healthy tomato plant leaves are a deep green, not yellow (link). They are also spread open. 

Leaf curling is common and usually caused by environmental stress, pests, disease, or herbicide drift.

When you see tomato leaves curling, it means your plants are reacting to something. Curling tomato leaves are a symptom. Now you need to look for the cause. 

For a thorough diagnosis, examine the plant and consider environmental factors. There may be other things along with curled leaves that will help you diagnose the problem. 

Other things to look for are:

Discoloration or yellowing

Spots or unusual textures

Insects hiding under the foliage

Distorted new growth

Weather conditions (high winds, heat waves)

Tomatoes are very sensitive to herbicides (weedkillers), especially heirloom tomatoes. Common chemicals used on lawns can cause tomato leaves to curl and plants to die. Even if you don’t use chemicals in your garden, herbicides can sneak in from herbicide drift and contaminated compost.

Herbicide drift happens when herbicide sprays are used nearby, and the wind causes them to “drift” onto the tomato plants. 

I’ve seen this happen in my own garden. Even though I don’t use lawn chemicals, my HOA does, and it has affected my plants near the common areas.

This often catches gardeners off guard because they don’t realize anything has happened until they notice the new leaves curling up.

Signs of damage from herbicide drift will be curled leaves that are also twisted and stunted. The new leaves are affected first. 

Another way herbicides can silently kill your tomatoes is through contaminated compost or manure. When horses eat hay from fields treated with weed killers, those chemicals pass through the horse and into the manure. Those harmful compounds, such as aminopyralid and clopyralid, can stay in the manure or compost for years.

Source: NC State Extension

If tomato leaf damage is from herbicide drift, it is possible for the plant to recover. Especially if there was minimal exposure. Watch the plant as new leaves appear to see if they start growing normally. The drift from a neighbor’s weed killer may only affect the new growth for a while. 

If it’s herbicide exposure in the soil, you’ll have to remove the plants. It can take time for the chemicals to break down and for the soil to be safe for planting.

When the soil is contaminated, you will see problems in your other plants too. Beans, peas, marigolds, and carrots are some of the other crops affected by herbicides.

Herbicides in compost and in the soil can take several years to dissipate. Source: UGA Cooperative Extension

When temperatures get hot enough, the leaves will curl to try to protect against water loss.

Water stress can be from too little water as well as too much. 

If mature leaves are curling in, it could be that the soil is not draining well. 

Did you do some extra pruning? Removing too much foliage can cause stress to the tomato plant. 

Be careful with those weeding tools! Root damage can cause leaves to curl. Also, transplant shock can be a cause of curled leaves. As long as the plant remains healthy, the roots will recover.

Sometimes curled leaves can be a sign of nutrient imbalances. This will be more evident with the older leaves first. Along with leaves curling, you should see color changes as well. Excess nitrogen can cause leaves to curl inward, and the leaves will also be a darker green. When there is too little potassium, the outer edges of the leaves will start turning yellow and then start curling. 

If you diagnose physiological issues, you can make adjustments and keep your tomato plant from dying. 

If your watering routine is perfect and the weather is mild, it’s time to grab a magnifying glass and look under the leaves.

When you carefully inspect the curled leaves, you may notice signs of insect damage. It can be tough to see, but insects can do damage to the plant long before the effects show. Whiteflies, aphids, and broad mites are all insects that damage leaves and can cause them to curl. 

Lastly, always check the whole plant, as curling leaves could be part of a bigger issue. Diseases will usually have other symptoms besides curling leaves. If the leaves are yellow or have a yellow-green mosaic pattern, it may be a tomato virus.

Check the reasons for leaves turning yellow.

There is a specific virus called Tomato Leaf Curl Virus that has spread to parts of the US. Infected plants will have new leaves that stay small, curl upward, and turn yellow between the veins. The plants will then have a tight, bushy appearance. Source: University of California IPM

Virus-infected plants cannot be cured and will have to be removed to help prevent the spread of disease.