Sow lobelia from late winter to mid spring on the surface of a good seed compost and gently firm down. Place the seed tray in a propagator at a temperature of 18-24C (65-75F) or seal it inside a polythene bag. Keep the soil damp but not wet. Do not exclude light as this aids germination which usually takes 14-21 days.
When seedlings are large enough to handle, transplant and grow them on in cooler conditions until large enough to plant outdoors. When lobelia plants are well grown and all risk of frost has passed, acclimatise them to outdoor conditions over 7 to 10 days. Transplant outdoors in full sun or semi-shade on moist, fertile, well drained soil at a distance of 10cm (4″) apart.