Start indoors 8-12 weeks prior to final spring frost. Sow thinly in seed trays and cover lightly. Cover seeds with a plastic bag or glass. Keep moist and warm at 18-24 C. Germination in 14-21 days. Remove cover when seedlings appear and thin out as required. Harden off and transplant after frost to well-drained soil. If grown as perennial, cut back each spring.