Why Are My Tomato Leaves Curling?
Most curling tomato leaves are nothing to worry about. Here is how to tell the harmless kind from the few causes that actually matter.
Curling tomato leaves are one of the most common things gardeners panic about, and most of the time the plant is fine. Tomatoes roll their leaves in response to stress, and in an Australian summer that stress is usually just heat and water. The trick is learning to tell that ordinary, harmless leaf roll apart from the two causes that genuinely threaten your crop: herbicide contamination and virus.
This guide walks through every common cause, how to identify which one you are looking at, and exactly what to do (and what not to do) for each.
1. Heat and water stress (the usual suspect)
This is the cause in the large majority of cases, especially from late spring through summer. When a tomato cannot move water up to its leaves fast enough, whether from heat, dry soil, waterlogged roots or sheer transpiration on a 38 degree day, it rolls its leaves upward and inward to cut the surface exposed to the sun. It is a self-protection reflex, not a disease.
The tell-tale signs are that it affects the older, lower leaves first, the leaves roll up and inward (often into tubes), the plant is otherwise green and growing, and it eases off in the cool of the morning or after a run of milder days.
What to do
- Water deeply and evenly. Aim for a deep soak that wets the whole root zone, then let the top 2 to 3 cm dry slightly before the next one. Avoid the bone-dry-then-flooded cycle that drives the worst rolling.
- Mulch heavily. A thick layer of straw or lucerne keeps the root zone cool and even, which is the single best fix for an Australian summer.
- Shade in extreme heat. On forecast scorchers, 30 to 50 percent shade cloth over the bed through the hottest part of the day takes the edge off.
- Leave the leaves on. They are still feeding the plant and shading the fruit from sunscald.
2. Herbicide damage (the one to rule out)
This is the most important cause to recognise because it is common, it is often misdiagnosed, and it can wreck a whole crop. Tomatoes are extremely sensitive to growth-regulator herbicides. The damage usually arrives through contaminated inputs rather than your own spraying: manure or hay from animals that grazed treated pasture, straw mulch, or bagged compost made from treated green waste. Spray drift from a neighbour or council verge can do it too.
The signs are different from heat roll. New growth at the top is affected, not the old leaves. Leaves become twisted, cupped, narrow and strappy, or take on a fern-like, feathery look. Stems can twist and thicken. The distortion gets worse toward the growing tip.
What to do
- Stop adding the suspect input immediately. If you mulched, fed or potted up just before symptoms began, that is your prime suspect.
- Flush container plants with plenty of clean water to leach residue, and keep feeding lightly to push clean new growth.
- Wait and watch. Mild contamination can grow out over a few weeks. Severe cases will not recover and the plants are best removed.
- Do not compost affected plants or the suspect mulch back into your veg beds. The residue persists.
3. Viral leaf curl
Several viruses cause curling, with tomato yellow leaf curl and similar viruses the best known. These are spread by sap-sucking insects, mainly whitefly and aphids. Virus is far less common than the first two causes, but it is permanent, so it is worth knowing.
The signs are curling and crinkling of the new growth, often with yellowing between the veins, a stunted bushy habit, and poor flowering and fruit set. You will usually see whitefly or aphids on the plant as well.
What to do
- There is no cure. Remove badly affected plants so they do not act as a reservoir for the insects to spread it further.
- Control the carriers. Manage aphids and whitefly with yellow sticky traps, a sharp hose blast and encouraging predators like ladybirds and lacewings.
- Grow resistant varieties next season if virus has been a problem in your area.
4. Broad mite and other less common causes
A few other things curl tomato leaves. Broad mite, too small to see without a loupe, twists and bronzes the new growth and is sometimes mistaken for herbicide damage. Very heavy nitrogen feeding can cause vigorous growth that rolls and cups. Hard pruning, especially removing too many laterals at once on indeterminate plants, often triggers a temporary curl as the plant rebalances. Cold snaps early in the season can also curl new leaves.
For all of these, ease off whatever is extreme, feeding, pruning, or exposure, and the plant usually settles. Broad mite needs a miticide or sulphur spray if it is confirmed.
How to diagnose your plant in three questions
- Which leaves are curling? Old, lower leaves means stress. New, top growth means herbicide, virus or mite.
- What does the curl look like? Simple rolling into tubes means stress. Twisted, fern-like, cupped or strappy means herbicide. Crinkled and yellowing with insects means virus.
- What changed recently? New mulch, manure or compost points to herbicide. A heatwave points to stress. A whitefly cloud points to virus.
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Open the App →Frequently Asked Questions
Should I cut off curled tomato leaves?
No. If the curling is from heat or water stress, the leaves are still feeding the plant and will often relax again in cooler weather. Removing them only adds stress and exposes fruit to sunscald. Only remove leaves that are clearly diseased or dying.
Will tomatoes with curled leaves still fruit?
Usually yes. Physiological leaf roll from heat, water swings or heavy pruning looks alarming but rarely affects the crop. The exceptions are herbicide damage and viral curl, which distort new growth and can reduce or ruin fruit set, so it is worth ruling those out.
How do I know if it is herbicide damage?
Herbicide damage shows as new leaves that are twisted, fern-like, cupped or strappy, often with the whole growing tip distorted. The usual source is contaminated manure, hay, straw or compost, or spray drift. If you mulched or fed just before it started, suspect the input.
Why are my tomato leaves curling up in hot weather?
Upward leaf roll in heat is the plant protecting itself. It curls the leaves to reduce the surface exposed to the sun and slow water loss. It is the most common cause in an Australian summer, it is harmless, and the leaves usually flatten out once temperatures drop.
Can too much water make tomato leaves curl?
Yes, both too much and too little. Waterlogged roots and drought both stress the plant into rolling its leaves. The fix is the same either way, aim for deep, even watering and let the top of the soil dry slightly between drinks rather than swinging between bone dry and soaked.
See also: How to Grow Tomatoes and the Pest and Disease Guide