What happened to my sunflowers?

[1Bee]

Sown on 2nd April, mix of J Arthur Bowers mpc and John Innes seed compost. Germinated in a growhouse in a reasonable timeframe. Some have come on enough to be potted up but still aren't what I would call happy. They were Titan, cut flowers mix and Ruby, from Suttons.

Any ideas?

[Zelenina]

I think those modules are way too small even for starting off sunflowers, especially Titans. They are big plants and I would've sown them in bigger pots. Their taproots probably reached the bottom almost as soon as they germinated and then had no place to go, which could be why they look unhappy. I suggest moving them all to bigger pots and see if they do better.

[1Bee]

Thanks Zelenina. Yeah, the plan was to just get them started and then move them on, but you make a good point.

[Briony]

I grow them in paper cups, I get them from a supermarket or from the pound shop. I know there is a slight issue with plastic contamination from the coating but they seem to do OK. I think the plainer the cup, the better as the more colourful ones have more dyes on them. Then the cup can be comopsted or burnt.