5 Reasons Your Tomato Leaves Are Curling—and How to Fix It, According to Plant Experts

Homegrown tomatoes taste like nothing else and add bold color to the garden. But it is frustrating when they don't grow the right way. One common issue you may encounter with your tomato plants is curling leaves that refuse to unfurl. This gardening woe has a few causes, but can be remedied once you find the source of the problem. Ahead, we chatted with gardening experts to find out why tomato leaves curl and how to fix this issue in time to yield amazingly juicy tomato fruits.

Physiological Leaf Curl

Not all leaf curling is bad. You typically don’t need to worry about curling leaves so long as your tomato plant looks healthy. "It’s just a physiological plant response to a temporary stress," says gardening expert Lindsay Springer. Stressors can include too much pruning, sun, wind, and water.

To avoid this problem, give your plants enough shelter and water. Using shade cloth on especially hot days is one way to safeguard your tomato plants from too much heat, says Springer, adding that this can protect plants from wind, too. Overwatering can also cause physiological leaf curl, so always check the soil for moisture before watering. 

Garden Pests

Garden pests can cause the leaves of your tomato plant to curl. "If you’re noticing leaf curl in addition to signs of leaf damage and discoloration—including small holes and brown or yellow spots—check for pests," says Springer. Possible culprits include aphids, thrips, white flies, flea beetles, stink bugs, hornworms, or spider mites. "Even if pests aren’t apparent at first glance, check the underside of younger leaves, towards the top of the plant, where you can see new growth versus the mature ones on the bottom," she says. 

There are a few ways to treat unwanted garden pests. One way is by growing tomatoes next to companion plants that help with pests like zinnias, cosmos, and others, says Springer. "These can attract pest predators to keep the tomato munching pests at bay throughout the season," she says. You can also buy natural pest repellents like neem oil, which require routine application to be effective.

Transplant Shock

Tomato plants can undergo transplant shock when they're moved outdoors. "Most plants aren’t used to changing environments, so they might curl and twist their leaves downwards to adjust to the sudden increase in sunlight, airflow, and heat," says Aimmie Altman, horticultural scientist at Bonnie Plants. Luckily, curling for this reason likely won’t damage the tomato plants in the long run, but could stunt or pause their growth.

The best way to avoid this is by helping your plants adjust to their new environment by exposing them to an increasing amount of sunlight daily, a process called 'hardening off.' Once temperatures warm, put your tomato plants outside for one hour the first day, two hours the next day, and so on. Do this for a week before transplanting.

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Inconsistent Watering

Tomato plants require a lot of water as they grow, says Altman. "If they dry out too much between waterings, the leaves will begin to curl downwards to try to conserve water." This process is exacerbated when the tomato plant is exposed to extreme heat. "When temperatures consistently reach or surpass 90 degrees Fahrenheit, tomato leaves curl downwards to conserve water," says Altman.

To fix the problem, gardeners should water their tomato plants consistently while avoiding over- or underwatering. Check your soil’s moisture levels before watering deeply, as increased rainfall or drought can affect your schedule.

Disease

Tomato plants are prone to plenty of diseases. Fungal disease is the most common of these ailments, says Springer, but you should always make sure you understand which disease is affecting your plant. "Refer to your local state extension resources, which can help you discern the specific disease pressures and effective remediation methods for your growing region," she says.

Depending on the tomato disease, treatment will vary. But you can prevent most diseases using the same methods. For example, space your plants far enough apart to receive adequate airflow throughout their lifecycle. "This might seem like a lot of empty space when plants are young, but they’ll fill in fast and need that airflow to remain healthy during their mature stages," says Springer. Also, remember to sanitize your pruning shears to prevent the spread of diseases from one plant to the next. "Just some alcohol or sanitizing wipes will do the trick," she says.