Using a good quality, moist seed compost, sow your seeds thinly in a propagator. Do not cover with compost as achillea require light to germinate. Place on a windowsill or in a greenhouse at approx. 18-21ºC (65-70ºF) to germinate (usually 10-14 days), avoiding direct sunlight. Transfer seedlings into seed trays spacing them 5cm (2") apart, and grow on. Acclimatise to outside conditions before planting out 25-41cm (12-16") apart where the plants are to flower.