They self sow very easily so you can either plant them in the spring in pots or sow some of them now in a seed bed as when they self seed they do it in the summer. Try it both ways.

I just scatter them where I want them and they come up easily.

Just scatter some on the ground where you want them to grow and also sow some in a seed tray or pots as well as insurance.

Chucking them round the garden when the seed pods open works for me.

Thanks everyone. A sort of related question. I had some gorgeous purple ones growing in a pot earlier in the year and cut them down as soon as they finished flowering as I'd read that I should get a second set of flowers. I haven't ( so far anyway - just have lots of leaves), will they grow again next year or have I now lost them?

They'll grow again next year, Bolton_lass, don't worry.

Phew!