M&C might not be quick enough if it's outside.
I don't think Centaurea montana is native to the UK. The annual cornflower is Centaurea cyanus
This is as Disponded IDd. a perennial from the mountains of southern Europe
Knapweed is usually applied to Centaurea nigra, (Lesser Knapweed), or Centaurea scabiosa, (Greater Knapweed)
A fair description Disponded
They won't fall over CraigB.
I sowed my cosmos in an unheated GH some weeks ago, they have been pricked out and have survived several frosty nights
Not too bad but you can plant them deeper than that
Doubt if they've rooted after 4 months. Take the flowers off, they don't need to be putting energy into that. That doesn't mean they won't root,
I see, back to mustard and cress then
Plant don't go from seed to flower in two weeks with the possible exception of hairy bittercress, but that's not colourful, Why two weeks if you've got months?