Tomatoes, ripe off the vines, are a revelation to anyone who has only ever eaten supermarket varieties.
However, every gardener who has ever attempted to grow home-grown tomatoes knows how incredibly sensitive tomatoes can be. A common complaint is curling tomato leaves. Which can affect the entire plant or sometimes just new leaves.
Rolling or curling leaves on tomato plants can be caused by many things. Including environmental stresses, pests & diseases, as well as chemical factors.
Below, we’ll go over all the reasons why your tomato leaves may be curling up. As well as ways to manage tomato leaf curl.
Heat, Wind, and Drought
Excessively hot, dry, and/or windy weather will cause your tomato plants to go into survival mode. Which results in leaves and leaflets curling up to prevent further water loss.
This symptom is called physiological leaf roll. Mild cases of tomato leaf roll do not affect yields or the quality of fruit. Once the weather cools down, leaves will usually return to normal.
However, in severe cases where temperatures consistently go above 85°F or 29°C, tomato plants may also suddenly lose their flowers. This is known as tomato blossom drop, which affects yields.
To avoid this, plant your tomatoes in partial shade, protect them from high winds, water often, and mulch your plants to retain moisture.
Too little or too much water will also cause your plants to be stressed and will result in tomato plant leaves curling.
Underwatering, like drought, is more common and will cause your plants to curl to conserve moisture.
Interestingly enough, overwatering may also drown and damage roots. Which prevents your plant from properly taking water and also results in leaf-curling tomatoes.
Give your tomatoes at least 1-2 inches (2.5-5 cm) of water per week. Divided between two heavy soakings per week. To allow the water to seep into the root system without becoming soggy.
While nitrogen is critical for plant growth, too much nitrogen also causes tomato leaf curl.
Tomatoes affected by nitrogen toxicity will have excessive and abnormally dark, thick green foliage, and leaves will often curl into a claw. Leaf tips will also bend down and leaves may also start to yellow. 
Use a fertilizer with about half as much nitrogen as phosphates and potassium (NPK ratio: 5-10-5 or 5-10-10) to avoid. If already displaying symptoms, try to flush the soil with pure water. Or amend the soil to correct the pH.
Heavy Pruning or Root Damage
Excessive pruning, especially of determinate (or bush) tomatoes, will also sometimes cause tomato leaves to curl. It’s easy to spot as leaves will usually only curl on parts of the stems that have recently lost their growing tips due to excessive pruning.
When pruning, focus on pruning only suckers between the main and lateral stems. Rather than pruning the growing tips, which stresses the plants.
Be careful when weeding around your plants or transplanting them to avoid physical injury to their roots. Which also causes leaf curling.
Broad Mites and Aphids
Broad mites look like tiny translucent yellow beads and will release leaf-curling toxins after feeding on young tomato leaves. Affected leaves will look like they have leaf roll. But may also show bronzed or russeted discoloration on the undersides.
Aphids will also feed on tomato plants, causing wilting, dead brown spots, and leaf curling and distortion. They are also vectors for other viruses. Like tomato yellow leaf curl and cucumber mosaic virus.
Spray affected plants with insecticidal soap or miticide in the case of broad mites. Horticultural oil such as neem oil is also effective in treating insects.
There are hundreds of potential tomato viruses that can cause leaf curling and stunted growth in tomatoes. Tomato plants affected by viruses will typically progress to a stage where yellow-green mosaic patterns will appear on the damaged leaves.
Yellow leaf curl virus, tomato yellow streak virus, tomato yellow mosaic virus, and the tomato yellow leaf curl virus are the common culprits in tomato leaves curling.
Most viruses are incurable, so it’s best to destroy affected plants. Control disease-spreading insects such as aphids, and practice good sanitation and crop rotation.
Herbicides in Wind, Mulching, or Manure
Tomatoes are extremely sensitive to herbicides and will let you know they’ve been affected with downward curling leaves. Or twisted or split stems, and malformed fruits that are not safe for consumption.
Herbicides will usually also affect the newest growth on the plant, which tends to be more sensitive.
Even if you don’t use herbicides, herbicides may still be transported upwind from neighbors. Or manure from farm animals that have consumed plants sprayed with herbicides, and in commercial mulches. 
Almost all pure grass or hay mulching will contain trace amounts of herbicides. Which help control weeds but also contain chemicals that cause tomato leaves to curl. Read the label carefully when buying mulches.
Herbicide damage may persist in soils for years. It’s important that you relocate garden beds or mulches. Then replant tomatoes that you suspect have been affected by herbicides. Also, avoid using manure or common weed killers near your tomatoes.
 Guan, W. (2018, June 1). Tomato Leaf Curling. Purdue University Vegetable Crops Hotline. https://vegcropshotline.org/article/tomato-leaf-curling/.
 Masabni, J., Ancisco, J., & Wallace, R. (2012, December). What Makes Tomato Leaves Twist or Curl? Texas A&M Agrilife Extension. https://aggie-horticulture.tamu.edu/vegetable/files/2010/ 10/E-626-What-Makes- Tomato-Leaves-Twist-or-Curl.pdf.