Sow from late winter to mid spring at 15-18C (59-64F) in a good seed compost. Sow ageratum seed on the surface of the compost and gently firm down. Keep soil damp but not wet. Do not exclude light. Germination usually takes 10-15 days. When seedlings are large enough to handle, transplant and grow them on in cooler conditions until large enough to plant outdoors. When ageratum plants are well grown and all risk of frost has passed, acclimatise them to outdoor conditions over 7 to 10 days. Transplant outdoors in a sheltered position in full sun on moist, fertile, well drained soil at a distance of 15-30cm (6-12″) apart.