Sow from February to April indoors at 21-24C (70-75F) in good seed compost. Just cover the seed with compost and keep the soil damp but not wet. Germination usually takes 5-14 days.They can also be sown outdoors where they are to flower during May once the soil has warmed. Keep moist until after germination and thin out to 20-25cm (8-10in) apart.
When seedlings are large enough to handle, transplant and grow in cooler conditions. Gradually acclimatise to outdoor conditions for 10-15 days before planting out after all risk of frost, 20-25cm (8-lOin) apart in a sunny spot.