Most of the time, curling tomato leaves are nothing to worry about. The usual cause is "physiological leaf roll" — a stress reaction, not a disease — and in a warm temperate summer it's the heat driving it. The giveaway is that it starts on the lower, older leaves, which roll upward and then inward, and go thick and leathery while staying a normal green. If that's what you're seeing, the plant is fine and will flower and fruit as normal. The two causes that do matter — hormone-weedkiller damage and tomato-potato psyllid — look different, and this article is mostly about telling them apart.

Read the leaves: which ones, and how

The diagnosis comes down to which leaves are affected and how they curl:

  • Old, lower leaves rolling upward, thick and leathery, still green → physiological leaf roll. Harmless.
  • New growth at the tips twisted, cupped or fern-like → suspect a hormone weedkiller.
  • Curling plus yellowing or purpling, with tiny insects underneath → tomato-potato psyllid.

The most common reasons

  1. Physiological leaf roll (most common, harmless). A response to heat, heavy pruning, irregular or excess water, high nitrogen, or root disturbance. In summer, heat is the usual trigger. The leaves look dramatic but the plant is unharmed — there's nothing to fix.
  2. Hormone-weedkiller damage. Here the new growth is distorted — twisted, stringy, fern-like — and the whole plant is affected, worst at the growing tips. It comes from spray drift, or from compost, manure, mulch or grass clippings carrying a persistent hormone weedkiller. This one's worth catching because it's easy to reintroduce every year without realising.
  3. Tomato-potato psyllid. A real, established pest in NZ, and under more pressure in warmer northern gardens. Look for curling with yellowing or purpling and stunting, and check the undersides of leaves for tiny winged insects and white sugary specks.
  4. Water stress or wind. Under-watered or wind-blasted plants roll their leaves to conserve moisture — temporary, and it eases when conditions do. Tomatoes want shelter from wind anyway.

What to do now

  • If it's the old leaves, leathery and still green — do nothing. Keep the water even, mulch to steady soil moisture, and don't over-prune. The plant is working normally.
  • If the new growth is twisted or fern-like, stop using whatever you recently added — a compost, mulch, manure or feed — as it may be carrying weedkiller. There's no cure for the affected growth, but clean new growth often outgrows a mild case. Never mulch tomatoes with clippings from a weed-and-feed lawn.
  • If leaves are yellowing with insects underneath, it's psyllid: check undersides, and pull badly affected plants rather than letting them infect the rest.

What to change next season

  • Keep watering consistent and mulch — steady moisture prevents most stress roll.
  • Give tomatoes full sun but shelter from wind, as our plant notes recommend.
  • Be careful what you mulch and feed with: the sneakiest cause of curled tomatoes is contaminated compost or lawn clippings introduced without a second thought.

Here, the honest odds are that your curling leaves are the harmless kind — so check the old-versus-new-growth distinction before reaching for any treatment.

Fruit not colouring up either? See Why Are My Tomatoes Not Ripening in NZ Temperate?, or explore the full NZ Temperate Planting Calendar →.