Curled leaves usually mean heat stress, underwatering, or a pest or disease problem
Tomato leaves curl for several reasons, and the cause matters because the fix is different for each one. The most common culprits are heat stress (leaves curl inward to reduce water loss), inconsistent watering (too dry or too wet), spider mites (tiny pests that suck plant juices), early blight (a fungal disease), and herbicide drift (accidental spray from nearby lawn treatment). Some curling is normal on very hot days and reverses when the plant cools down. Other curling signals a problem that will spread if you do not act.
The fastest way to narrow down the cause is to look at where the curling starts, whether the leaves feel dry or soft, and whether you see spots, webbing, or insects. A plant stressed by heat alone will recover within hours of the temperature dropping. A plant with spider mites will get worse every day until you treat it.
Key Takeaways
- Inward-curling leaves on a hot day usually mean heat stress and will uncurl when the plant cools, but curling that persists or spreads needs investigation.
- Spider mites cause fine webbing on the undersides of leaves and tiny yellow spots; they thrive in hot, dry conditions and multiply fast without treatment.
- Early blight starts with brown spots and rings on lower leaves, then spreads upward; remove affected leaves and improve air circulation to slow it.
- Watering deeply but less often (so soil dries slightly between waterings) prevents both drought stress and the root rot that comes from constant wetness.
- Herbicide drift from nearby lawn or garden spray causes cupped or twisted new growth; there is no fix, but the plant may recover if the spray was light.
Heat stress and when curling is temporary
On days above 85°F, tomato leaves often curl inward at the edges. This is the plant protecting itself by reducing the leaf surface exposed to the sun and heat. The curling usually reverses by evening or the next morning when temperatures drop. This type of curling is not a problem unless it happens every day for weeks, which signals the plant is struggling to keep up.
If your plant is in full sun and temperatures are consistently above 90°F, shade cloth (30 to 50 percent shade) can help. Mulch around the base to keep soil cooler and more consistently moist. Water early in the morning so the plant has moisture available before the heat of the day. If the curling is temporary and the plant is otherwise healthy, no treatment is needed.
Spider mites: the pest that thrives in heat and dryness
Spider mites are nearly invisible to the naked eye but cause distinctive damage. Look for fine webbing on the undersides of leaves, tiny yellow or pale spots on the leaf surface, and leaves that curl, yellow, and eventually drop. The damage usually starts on the lower leaves and moves upward. Spider mites multiply rapidly in hot, dry conditions — a population can explode in two to three weeks.
Check the undersides of affected leaves with a magnifying glass or by holding a white paper under a leaf and tapping it; live mites will fall onto the paper as tiny moving specks. If you see webbing or mites, spray the plant thoroughly (tops and undersides of leaves) with water from a hose every two to three days for two weeks. This removes mites and webbing and raises humidity, which spider mites dislike. If the infestation is heavy, neem oil or insecticidal soap applied according to label directions will speed recovery. Avoid sulfur sprays on tomatoes in heat above 85°F, as they can damage the plant.
Early blight: a fungal disease that spreads from the bottom up
Early blight starts with brown spots and concentric rings (like a target) on the lowest leaves. Leaves yellow around the spots, then curl and eventually drop. The disease moves upward as the plant grows. It thrives in warm, wet conditions and spreads through water splash from rain or overhead watering. Unlike heat stress or spider mites, early blight will not go away on its own and will eventually defoliate the plant if untreated.
Remove all affected leaves as soon as you see them, cutting them off at the stem and disposing of them in the trash (not compost). Do not compost diseased plant material. Water only at the soil level, never overhead, and water early in the morning so any splash dries quickly. Improve air circulation by pruning lower branches and spacing plants so air moves freely. If the disease is spreading despite these steps, fungicides containing chlorothalonil or copper can slow it, but prevention through good air flow and careful watering is more effective. Once a plant has early blight, it will likely have it again next season, so rotate where you plant tomatoes each year.
Underwatering and overwatering both cause curling
Tomato plants need consistent moisture — not soggy, not bone dry. Underwatering causes leaves to curl inward and become papery and brittle. The plant is wilting because the roots cannot pull up enough water. Overwatering (or poor drainage) causes root rot, which also leads to wilting and curling because the roots are damaged and cannot absorb water even though soil is wet.
Water deeply once or twice a week, depending on heat and rainfall, so water reaches the full depth of the root zone (usually 8 to 12 inches). Let the top inch of soil dry out between waterings. Stick your finger into the soil; if it is dry at the first knuckle, water. If it is still moist, wait. Mulch around the base with 2 to 3 inches of wood chips or straw to keep soil temperature steady and reduce evaporation. In very hot weather, you may need to water more often, but the principle stays the same: water deeply and let it dry slightly between waterings.
Herbicide drift from lawn or garden spray
If you or a neighbor recently sprayed a lawn or garden with herbicide (weed killer), and your tomato plant's new leaves are cupped, twisted, or unusually small, the plant may have been exposed to herbicide drift. The damage is done and cannot be reversed. New growth that emerges after the spray settles will be normal.
Light exposure usually does not kill the plant, though it may slow growth for a few weeks. Heavy exposure can kill the plant. There is no treatment; you can only wait and see whether new growth recovers. To prevent this, do not spray herbicides on windy days, and keep spray away from vegetable gardens. If you hire someone to spray, tell them where your tomatoes are.
When to remove leaves and when to leave them alone
Remove leaves only if they are diseased (spotted, with rings, or showing clear signs of blight), heavily infested with spider mites, or completely dead and brown. Do not strip the plant bare in an attempt to improve air flow; the leaves feed the plant and produce the energy it needs to grow fruit. Removing a few lower leaves for air circulation is fine, but removing more than one-third of the foliage at once stresses the plant.
If leaves are straightforward curled from heat or temporary drought, leave them alone. They will uncurl as conditions improve. If leaves are yellowing but not spotted or webbed, they may be natural senescence (the plant dropping old leaves as it grows), and you can remove them or leave them.
Frequently Asked Questions
Can I use the same fungicide for early blight and spider mites?
No. Early blight is a fungal disease and needs a fungicide. Spider mites are pests and need an insecticide or miticide. Using the wrong product will not help. Water spray works for spider mites but not for fungal disease. If you have both problems, you may need two products, or you can focus on the one causing more damage first.
Is curling on new leaves at the top of the plant different from curling on old leaves at the bottom?
Yes. Curling on new growth at the top usually means herbicide drift, heat stress, or inconsistent watering. Curling on lower leaves that spreads upward usually means early blight or spider mites. Lower leaves naturally yellow and drop as the plant grows, so some loss there is normal.
What temperature is too hot for tomatoes?
Tomatoes grow well up to about 85°F. Above 85°F, pollen becomes less viable and fruit set drops. Above 95°F, the plant is under serious stress. Consistent temperatures above 90°F will slow growth and increase pest and disease pressure. Shade cloth and consistent watering help the plant cope.
Should I prune curled leaves to improve air flow?
Only if the leaves are diseased or heavily infested. Healthy curled leaves still photosynthesize and feed the plant. Removing too many leaves at once stresses the plant more than the curling does. Remove one or two lower leaves at a time if you want to improve air circulation, but do not strip the plant.
Can I save a plant with severe early blight?
If the disease has spread to the upper leaves and the plant is heavily defoliated, it will struggle to produce fruit and may not recover enough to be worth keeping. If only the lower third is affected, remove those leaves, improve air flow, and water carefully; the plant can often recover. Once a plant has early blight, it is prone to it again, so consider replacing it next season with a resistant variety.