Tomato Plant Leaves Curling? 7 Causes and Ways to Fix It

Keeping your tomato plants healthy is the key to a bountiful harvest. If your tomato plant leaves are curling, you may be wondering if your harvest is at risk. Fortunately, curled leaves aren’t always cause for concern. 

Leaf curling in tomato plants can be caused by a wide array of factors, many of which can be corrected. The key is to identify the root cause quickly so you can make the necessary adjustments to get your plants back on track. 

Here’s what you need to know about the causes of leaf curling in tomato plants and what you can do to fix it.

1. Extreme Temperatures

Like many vegetables, tomato plants thrive in warm daytime temperatures ranging from 70-85℉ and slightly cooler nighttime temperatures of 55-75℉. As long as they’re watered well, tomatoes may survive in warmer temperatures but periods of extreme heat can cause the plant to dehydrate more quickly. 

Curling leaves are often a sign that a tomato plant is suffering from the heat. Prolonged periods of high temperatures over 90℉ can cause stress, and curling leaves are usually a sign that the plant is working hard to conserve water.

If you suspect your tomato plant leaves are curling due to extreme temperatures, there are a few things you can do to help. Try using a shade net or cloth to shield the plant from the heat and sun. And don’t forget to water regularly so the soil doesn’t dry out too much.

2. Excessive Sunlight

Your tomatoes need plenty of sunlight in order to thrive, but too much sun can be stressful or even damaging. Ideally, tomato plants should get at least 6-8 hours of sunlight per day. They may be able to tolerate more, depending on the average daytime temperature.

If your tomato leaves are starting to curl and heat doesn’t seem to be an issue, it could be the amount of sun the plants are getting. Excessive sun (especially on high UV days) can burn the leaves, causing them to yellow and dry up. 

Again, protecting your tomato plants with a shade net may help. If excessive sunlight is a prolonged issue, consider moving your tomatoes to another location. It’s easy enough if they’re growing in containers in a patio garden, but transplanting in-ground plants can be a little trickier.

3. Inadequate Watering

In order to produce nice juicy tomatoes, your plants need plenty of water. And high temperatures or excessive sunlight can increase the water demands of a healthy tomato plant. If your tomato plant leaves are starting to curl, they might not be getting enough water. 

Here are some options for keeping your tomatoes well-watered:

• Plant your tomatoes in the ground - Tomato plants grown in pots are more vulnerable to underwatering because they dry out more quickly.
• Water in the early morning - Avoid watering your tomato plants during the heat of the day. Watering in the morning ensures the water has time to soak in instead of evaporating.
• Keep the soil consistently moist - You want to avoid alternating between periods of dry soil and over-damp soil. Try to develop a watering routine that keeps the soil moist but not wet.
• Consider automatic watering - To reduce the hassle of watering, consider an automatic water system like drip irrigation or an olla (a porous terracotta pot buried in the soil). 

Keep in mind that overwatering can be problematic for tomato plants as well. Too much water can lead to root rot which may cause the leaves to turn yellow and die. It could also contribute to powdery mildew or leaf rot.

4. Nutrient Imbalances

Maintaining proper nutrient balance is essential for healthy plants and robust tomatoes. The best thing you can do to prevent nutrient imbalances is to test your soil before planting and amend the soil as needed. You can also use fertilizer throughout the growing season, but it can be tricky to get the balance of nutrients consistently right.

Some of the nutrients most likely to cause leaf curling in tomato plants are:

• Nitrogen - Too much nitrogen can cause the plant to produce more leaves than the nutrients and water in the soil can sustain, leading to leaf curling and drooping.
• Potassium - Inadequate potassium can cause stunted growth with lower fruit production and yellow or curling leaves.
• Phosphorus - Like potassium, low phosphorus levels can reduce growth and fruit production and cause the leaves to curl or yellow.

If you test your soil and find that it’s lacking in nutrients, adding compost could be a quick fix. Purchase organic compost to mix into your soil or consider making your own at home.

5. Viral Disease

Even if you do everything right in terms of planting, watering, and fertilizing your tomato plants, they are still susceptible to disease. Viruses, in particular, are common in tomato plants and can cause stunted growth and leaf curling.

The two most common viral diseases that cause leaf curling in tomato plants are tomato mosaic virus and yellow leaf curl virus. Both of these are spread by insect pests like whiteflies. 

Unfortunately, there’s no cure for viral diseases. The best thing you can do is try to control the spread by removing infected plants and disposing of them properly.

6. Pests

Several pests that tend to target tomato plants can cause the leaves to curl up and eventually die. In many cases, it’s because the pests suck the sap out of the leaves which leads to dehydration. If you catch it early when the leaves are just starting to yellow or curl, you may be able to prevent the plant from being killed.

Some of the pests that can cause leaf curling in tomato plants include:

• Tomato pinworms - These tiny worm-like creatures are actually the caterpillar form of a moth in the family Gelechiidae that targets tomatoes in warm climates.
• Broadmites - Tiny arachnids which can be difficult to spot with the naked eye but can be identified by their unique clusters of glass-like eggs.
• Aphids - These small, pear-shaped, soft-bodied insects range in color from yellow, brown, and green to black and even red.

Dealing with pests on tomato plants can be tricky, as it generally requires a multi-step approach. Start by removing as many of the pests as you can, either by hand or by spraying the plant with water. Then treat the plants to kill any remaining pests and take measures to prevent reinfestation. Keeping your garden tidy and free from organic debris can help.

7. Weed Killer

If you’re trying to grow healthy tomato plants, you probably put some effort into weed control. Weeds can crowd your tomatoes and take valuable nutrients from the soil. But if you’re using herbicide to kill weeds, it might have a negative impact on your tomato plants.

Tomatoes are notoriously sensitive to herbicide—even a little bit of accidental exposure can lead to problems. If the leaves of your tomato plants are starting to curl downwards, it’s worth considering whether a nearby herbicide application may have drifted too far.

To prevent herbicide drift from affecting your tomato plants, consider switching to natural weed control methods. You can pull bigger weeds by hand but if you have a very large garden, an organic spray formula made with citric acid, clove oil, or citrus oil might be more effective. It may also be worth investing in a pre-emergent herbicide that prevents weed seeds from germinating.

Final Thought: Curled Leaves Aren’t Always a Problem

If your tomato leaves are starting to curl, don’t panic. You may still have time to fix the problem before it causes fatal damage to your plants. Just be careful not to overcorrect or you might accidentally cause stress that leads to other issues.

To ensure a bountiful tomato harvest, it’s crucial to start with strong seedlings and to stock up on essentials so you’ll have them on hand when needed. 

At Park Seed, you can shop our curated collection of tomato supplies including cages, fertilizers, plant protectors, and more. And don’t forget to order your tomato seeds early enough to get them started before planting them in your garden or containers.