Sow outdoors where they are to flower. Prepare the ground well and rake to a fine tilth before sowing. Sow 20mm ( 3/4in) deep, in rows 30cm (12in) apart.For earlier flowering: Sow seed, 1cm (1/2″) deep, 3 seeds per 7.5cm (3in) pot, in free-draining, damp seed compost. Place at 20-29C (68-86F) until after germination. Gradually acclimatise to outdoor conditions before planting out after risk of frost. Before planting into containers, ensure plants are well rooted in their pots.
When large enough to handle, thin out seedlings to 23cm (9in) apart.