Hi, you can sow them now and overwinter in your greenhouse or polytunnel, sow them in individual pots, which should be the long tom type, or you can use root trainer pots, when they get to about 3 or 4" stop them, and they will get more bushy, and are bigger plants for planting out at the end of may, [depending where you are] you can also sow them in early spring, this method will give you an extended flowering season, Derek.

I use the cardboard middle from a loo roll and pop 2 seeds per roll. kept just damp in the unheated greenhouse they grow away earlier than those planted in spring.