Why are my tomato leaves curling?

The 4 most likely causes

The cause of tomato curling leaves usually narrows to one of the items below, ranked by how often we see each in Growli's diagnostic chats. Work down the list — most readers find their answer in the top two.

1. Heat stress or sudden temperature swing (Most likely)
   Leaf roll on tomato is the plant's way of reducing surface area when air temperature spikes above 30°C/85°F or after a cold night follows a hot day. The curl is upward and the leaves stay otherwise healthy. Mulch heavily and water deeply at dawn to buffer the swing.
2. Underwatering or letting it dry too long (Likely)
   Underwatering looks similar to overwatering at first — both produce limp, dull leaves — but the soil tells the truth. If the soil is dust-dry several centimetres down, water deeply. Tomato prefers deep watering 2-3 times per week, more in heat.
3. Aphids on new growth (Likely)
   Aphids cluster on the softest new shoots of tomato, sucking sap and curling new leaves as they go. Look closely at the growing tips and undersides of the youngest leaves. A blast of water followed by insecticidal soap clears most infestations.
4. Herbicide drift or contaminated compost (Possible)
   If new tomato growth is twisting, fern-like, and oddly stretched, suspect herbicide drift from a neighbour's lawn or compost made from treated grass clippings. There is no cure — affected plants usually recover the following season once the chemical breaks down.

Why tomato in particular

Tomato leaves curl for reasons that range from harmless to serious, so read the pattern. The commonest is physiological leaf roll: older leaves cup upward along the midrib in a heatwave or after hard pruning, stay green and firm, and cost you nothing. Downward, twisted, corkscrew growth at the shoot tip instead suggests herbicide drift, and upward curling with stunting and thickened, yellowed new leaves can signal a whitefly-borne virus. Uniform upward roll on the lower leaves is the reassuring one.

Normal turnover, or real trouble?

Many tomatoes, vigorous indeterminate types especially, roll their lower leaves upward into tight tubes in the weeks after a hard prune, a heatwave, or a heavy soaking, then simply carry on fruiting; the leaf stays thick, green and leathery. That upward roll on older leaves, fairly uniform across the plant, is the harmless kind that costs no crop. The worrying pattern is new shoot-tips that twist, thread and distort while staying pale and stunted.

How to diagnose in 60 seconds

Run these quick checks before you change anything — the right fix depends on what you find.

• Is the curl upward (cupping) or downward (rolling)? Upward usually = heat or light stress; downward usually = water or pest issue.
• Check the newest leaves first — pests and herbicide damage hit new growth fastest.
• Tomato wants water deep watering 2-3 times per week, more in heat. Push a finger into the mix and hold it against that: still damp well before it is due, alongside the symptom, is the overwatering signature.
• Check the underside of curled leaves for spider mites, aphids, or thrips with a phone-camera macro.

The fix — step by step

The first thing to rule out is not the plant but its surroundings. Check whether a lawn weed-and-feed, a hormone weedkiller, or drifting spray has reached the bed, or blown in on grass clippings used as mulch, because that fern-leaf twisting at the growing tip has no cure and the plant is best pulled. If instead it is plain upward leaf-roll, change nothing: keep the watering even, let it ride, and it will fruit.

This is the recovery sequence Growli walks users through for tomato with curling leaves. Work through the steps in order; skipping ahead is the most common reason a plant fails to bounce back.

1. Identify the curl direction. Upward cupping points to heat or light stress; downward rolling points to water stress, pests, or cold shock. The fix depends on which one you see.
2. Inspect leaf undersides for pests. Hold a phone torch behind a curled leaf — spider mites show as fine webbing, aphids as clusters of green or black dots at the growth tips, thrips as silvery scrapes.
3. Adjust water or microclimate. If the soil is bone dry, soak tomato thoroughly. If the room is below 40% humidity and the species is humidity-loving, add a humidifier. If heat is the issue, move out of direct midday sun.
4. Treat any pests at the source. Rinse pests off in the sink, then spray leaf undersides with insecticidal soap or a neem-oil mix every 5-7 days for three weeks to break the egg cycle.
5. Wait for new growth. Curled leaves rarely uncurl. New growth will tell you if the cause is fixed — if the next set of leaves comes in flat, you have solved it.

When this can't be saved

Most cases of tomato curling leaves are recoverable, but a few red flags point to a plant that has gone past the point of return. If you spot any of these, consider propagating a clean cutting and starting over.

• New growth is thin, twisted, and fern-like (a classic herbicide-damage signature on tomato).
• Curl is paired with mosaic-pattern discolouration — that points to a viral infection with no cure.
• Every leaf curls within 24-48 hours of a single event — usually permanent shock damage.

Prevention

For tomato, the single biggest preventative is matching its native rhythm: deep watering 2-3 times per week, more in heat, 6-8 hours of direct sun, and a free-draining pot with a working drainage hole. Outdoor edibles benefit from a thick mulch layer that stabilises soil temperature and moisture, both of which reduce curl. For indoor plants, keep a digital hygrometer in the room and aim for 50% humidity — humidifiers or pebble trays close the gap cheaply.

Common questions

Related guides

• What's wrong with my plant? — the diagnosis apps compared
• Tomato care guide — full watering, light, and feeding routine
• Is tomato toxic to cats and dogs? — toxic to pets, per the ASPCA
• How often to water tomato — the watering brief
• When to repot tomato — pot size and timing
• Curling leaves on plants — the full diagnostic guide across species
• What's wrong with my plant? — Growli's flagship diagnosis index
• Tomato — yellow leaves
• Tomato — drooping
• Tomato — brown spots
• Monstera — curling leaves