Why are my tomato leaves curling? 5 common reasons and what you can do to fix it, according to experts

If you love to check on your garden every morning, you’re likely in tune with every new stem, flower, and fruit that pops up. But if you’ve noticed something unusual about your tomato plants recently, you might be wondering: Why are my tomato leaves curling?

While the idea of growing tomatoes sounds easy, the reality is that growing any fruit or vegetable comes with its challenges. You need to repot tomato seedlings at the perfect time, and you need to make sure that you’re tapping your tomato plants (yes, really!). Not only that, but you also need to keep an eye on them for any visible changes that may cause concern.

And if you spot tomato leaf curl on your tomato plants, you should do everything you can to fix it. But first you need to understand what’s causing it in the first place, which is where we come in. Here are the 5 common reasons why your tomato leaves are curling.

1. Unstable temperatures

You probably don’t need us to tell you that the British weather is unpredictable. During the summer months, we can have pouring rain one minute and a scorching heatwave the next.

And while tomatoes are fairly used to the changing weather, they still struggle when the temperatures are unstable. For example, they don’t enjoy being out in the soaring heat - and plant heat stress is one of the reasons why your tomato leaves may be curling.

Morris Hankinson, Director of Hopes Grove Nurseries, explains, ‘High temperatures can cause damage to the leaves, and by curling, the plant reduces the amount of direct sunlight hitting the leaves, therefore lowering their surface temperature. This curling also helps the plant save water by reducing the surface area exposed to the sun, which lowers water loss through evaporation.'

‘Additionally, the rapid rate of water loss in hot weather can outpace the roots' ability to absorb water from the soil, leading to an imbalance. This water uptake imbalance stresses the plant, causing the leaves to curl to protect themselves,’ he adds.

Morris Hankinson

Morris Hankinson is the founder and managing director of Hopes Grove Nurseries Ltd, the UK’s only specialist grower-retailer of hedging plants. He established the thriving business in 1992, shortly after graduating with a Commercial Horticulture Degree from Writtle College, Essex.

Solution: If you’ve grown tomatoes in pots, aim to move them out of direct sunlight when it’s going to be a hot day. You should also water them regularly and consider a drip irrigation system to ensure they’re getting as much water as they need. This will also prevent you from overwatering your plants in the summer.

If they’re too cold, consider moving them into a greenhouse or covering them with a plant cover until the cold snap is over. Mulching your plants can also help to maintain a constant temperature during both hot and cold weather, too.

2. Underwatering or overwatering

It’s surprisingly easy to make garden watering mistakes - especially when it comes to your tomatoes. And if you’re wondering why your tomato leaves are curling, it may be that you’re either underwatering or overwatering your tomato plants.

When watered incorrectly, tomato plants curl their leaves and turn yellow. Your plant will also likely struggle to fruit, resulting in a poor tomato harvest.

Solution: If you want to save your tomato plant from underwatering or overwatering, you first need to understand the current conditions. So, it’s best to check the moisture level of the soil to see whether it has more or less than it needs. Then, you can change your watering schedule to suit the results.

Generally, tomatoes like to be well-watered, but they don’t like to be in waterlogged soil. If your soil is too moist, reduce your watering schedule. If your soil is too dry, take your watering up a notch.

If it's hot, you should also make sure that you water your plants in the morning rather than at night.

3. Nutrient deficiency

Tomatoes are hungry plants, and while good-quality soil and water may be enough to produce a happy and healthy plant, you’ll likely need to feed your tomatoes throughout their growing season.

If you don’t, you may find that your tomatoes don’t turn red, and your tomato leaves start to curl. If this happens, there’s a high chance that your plant is deficient in valuable nutrients - or perhaps even overloaded. And if you want your tomato leaves to uncurl, you’ll need to make some changes.

As Graham Smith MCIhort, a gardening expert from LBS Horticulture, explains, 'If you have soil that is too high in nitrogen, your tomato plant may produce too many leaves that cannot be sustained by the nutrients in the soil. This can make the leaves begin to curl or droop.'

He adds, 'Similarly if your soil is lacking in potassium or phosphorous, the growth of your tomato plant may be stunted, which can lead to less fruit and curling leaves.'

Solution: First, you should check for nutrient deficiencies in the soil using a test kit - like this BoltSafe Professional Soil Test Kit from Amazon - to find which nutrients your plants lack. Then, you can find a fertiliser that will bump up these deficiencies.

In most cases, this will be a specific tomato feed, but you can also make your own tomato fertiliser if you want to save some money.

4. Diseases, viruses, and pests

If you’re wondering why your tomato leaves are curling, your plants may be diseased, have a virus, or be riddled with pests. Unfortunately, tomatoes regularly fall victim to these problems, and curled leaves are often associated with poor fruiting, mottled leaves, stunted growth, and more.

It can be hard to pinpoint exactly which problem your tomato plant is dealing with, but tomato mosaic virus and yellow leaf curl virus are the most common. In many cases, they’re spread by the pests in your garden - which is why it’s particularly important to know how to get rid of glasshouse whiteflies.

Solution: As these diseases and viruses are often spread by garden invaders, you should aim to get rid of garden pests as soon as possible. There are different ways that you can do this, but we’d suggest planting pest-repellent plants near to your tomatoes and maybe even using nematodes to your advantage.

While doing this, you should also separate your diseased tomato plants from your healthy-looking plants. This will prevent the spread and keep your other plants safe from leaf curl.

5. Exposure to weed killers

If it feels as though you spend your whole life trying to get rid of weeds, you’re not alone. But if you’re still using chemical weed killers, you may be having a bigger impact on your garden than you think. After all, the exposure to weed killers can result in tomato leaf curl.

Tomato plants are particularly vulnerable when it comes to hormone weedkillers, and using them on the other side of the garden can still affect them. If the tiniest speck of residue is picked up by the wind and carried over to your tomato plants, they may still suffer the consequences.

Solution: If your tomato plants have been exposed to chemical weed killers, there’s not a whole lot that you can do to help them. They may be able to survive the ordeal, but they may also never recover. So, it’s best to continue caring for them as normal and hope for the best.

There are ways that you can prevent this from happening again, though. Instead of using chemical weed killers, use natural solutions instead - no matter whether you want to get rid of weeds in a lawn or get rid of weeds in gravel.

FAQs

Can tomato leaf curl spread to other plants?

If your tomato leaf curl has been caused by a virus or disease, there’s a high chance that it will spread to other plants. That’s because these diseases are often carried and spread by garden pests.

If your tomato leaf curl has been caused by underwatering, overwatering, nutrient deficiency, or unstable temperatures, however, the tomato leaf curl won’t technically spread to other plants. However, it’s important to note that they’ll still probably be affected if they’re in similar conditions.

How do I stop my leaves from curling?

To stop your leaves from curling, you first need to understand why they’re curling. In most cases, the leaves of plants - including tomato plants - will curl because of heat stress and unstable temperatures.

Because of this, you should aim to move them away from the heat and provide them with some shade to prevent scorching. You should also water them regularly, making sure the plant has enough moisture to survive the warmer temperatures.

If your tomato leaves are curling, you should now have all of the knowledge and tools at your disposal to fix it!