Sow in a propagator on a windowsill or in a greenhouse at approximately 15-18°C (60-65°F) pressing the seed lightly onto a good quality finely sieved, moist compost. Do not exclude light or allow to dry out (Germination 10-14 days). Transplant seedlings, spacing them out 5cm (2") apart in trays and grow on. Plant out 30cm (12") apart in a sunny position after the danger of frost has passed. Ageratum has an interesting meothod of protecting itself against insect attack, it produces a chemical which can cause sterility in the insect pests.