When to pot on seedlings?

[LookingOptimistic]

I've grown a bunch of flowers from seed and wondering how big they have to be to pot on from their plugs?

The ones pictured are marigolds, calendular and some cosmos. Particually not sure about the marigolds, do the roots have to be more established still?

The marigolds could be transplanted, but there’s no need to, they’re quite happy where they are. They’re easier to repot when the roots have filled the pot because it holds all the soil together. You’d probably repot into a 8cm pot and that’s no bigger than what they’re in at the moment.

the ones in the last picture are barely showing their first true leaves so a long way from being ready.

Those marigolds could stay where they are until you plant them out. The others are still too small to pot on.

If your Cosmos start getting a bit too tall and floppy you can repot them lower down in taller pots but they all look fine just now.

@MereDintofPandiculation Thanks very much, i will leave the marigolds as they are then (doing better than other years as have strong straight stems).

@AlliumFairy Ah i see, will wait for cosmos to have more pairs of leaves.

@Fizzadora It might get to point they are bit too tall and floppy as some already have quite long stems, will see how they go and pot them on if need be.