Seedlings - Greenhouse or Indoors?

Hi everyone

I have a PVC greenhouse and have a few seedlings growing in there currently such as cornflower.

I also have lots of seedlings growing indoors on windowsills... I have marigolds, sweet sultan, petunias, stocks, peppers, busy lizzies, pansies, alyssum and salvias.

My question is... once these seedlings appear, can they be moved straight into the greenhouse? What would you advise? This is because the marigolds, especially, seem to go really leggy when kept on a windowsill too long.

I appreciate any advise, I'm really stuck on this!

Thanks,

Kay x