Why are these leaves turning white?

[superoz]

I started off some Hollyhocks in seed trays, as they grew bigger a few of them had leaves turning white.
Does anyone know why this is happening?

Maybe a soil deficiency?

It's a magnesium deficiency when the leaves go pale like that between the veins.

Do you have any Epsom salts? If so, then dissolve a small pinch in about a litre of water and give it that as a one-off. Then use Miracle Gro liquid fertiliser according to the pack instructions once a fortnight and keep well-watered in between.

Thank You! I haven’t got any Epsom Salts but will try to get hold of some. Sounds like this will fix the problem.