Serious lack of water. It looks as if you are growing the plant in peat... not a good idea. Keep watering!

It's worth a try, but I suspect that that one is a goner. Sunflowers aren't very forgiving about wilting.

These dwarf sunflowers are quite frankly a waste of time. Once the flower head has developed, the roots will simply not take over watering in a large pot. Sorry, but never, ever buy these again.

....the larger types (in the ground) are fine.

So which is it then, over watering or under watering? Looks like under watering to me.

Sunday and Monday were the hottest days, and the Sunflower was watered well in the morning a couple of hours before the sun came round, and then again in the evening once the Sun had dried the compost. The pot also has good drainage.

The compost used by me is peat free. It came in a very small pot, as it was very small, so if the pot had peat it would only be a small amount.

Thanks for your suggestions even if some people reckon the opposite to the others. (under / overwatering).

Still looks like under watering to me too... Fractal

The Sunflower has now been removed and replaced with a nice red New Guinea Busy Lizzy. Looks much better than an ill Sunflower.

I grew the miniature one, as I do not have any room for a large giant one. I prefer the giants though, plus there is no soil round the front where we get hours of Sunlight, so I had to be able to pot one up.

Shame, but hay ho.