Hi All, I too am seeing the leaves on my tomato and chilli plants curl. I can see a variety of possible reasons suggested above and may try to think of a way to test for each with the 3 mature plants that are doing it. But have also provided some pictures below, in case anyone is able to help me pinpoint the cause. As a bit more background, all three of the taller tomato plants I purchased from a garden centre, though I am starting to see some signs of curl on my grown from seed ones and am seeing it on some of my chilli plants all grown from seed. All plants have been sitting on a window sill temperatures probably 13c lowest, 18c average. On watering, it's my first time growing, reading lots of conflicting advice, had been keeping tomato plant soil very moist and chilli plant soil a lot less. I have been potting on regularly, I've checked for bugs and not found any. Any ideas welcome:
Giles, there is a lot of conflicting advice about watering. I can only say that, after 25 years of growing these critters, less is better. From what I can make out from the photos, the curling looks like too much moisture. Let the mix dry out between watering, and if the pots are sitting in saucers, empty excess water from the saucers. You could probably also do with some more daytime warmth if you can manage it.
There's a general tendency to pamper tomato plants. They don't need it. They're tough critters that will produce in the most surprising conditions. In fact, they're a plant that will thrive on a certain amount of neglect. If they're feeling a tad vulnerable, they will seek to reproduce themselves - by producing fruit. Pampered, they will never feel vulnerable.
You're on the right track with the chillies. Chillies and toms are grown exactly the same way. I'd apply your chilli method to your toms.