Sow very thinley in either ground or container in prepared soil at the begining of May. Beware that they are a magnet for blackfly though.

the self sown ones in my border start to germinate in late April/early May. Though when my girls were little we used to sow them at the end of March in the unheated greenhouse. Frost will kill them so the early sown ones were kept in the greenhouse and planted out early June.

Blackfly not a problem here, but appreciated by the white butterflies.

They flower better if grown in poorer soil so no need to add fertilizer to help them.

Thanks to all

They grow so easily when sown outside I wonder whether its worth the effort of potting and potting on?

My self sown ones are already germinating outside, Hampshire.
As SteraG says, they grow so easily but perhaps if a choice colour etc then maybe worth that bit of effort