Sow directly outdoors after the last spring frost when nights stay above 50F (10C). Or start seeds indoors, 4-6 weeks before last frost. Grow in fertile, well-drained soil spacing seeds 5-6 inches apart. Thin to stand 12-15 inches apart. When seedlings are 3-4 inches tall, pinch back the tip of the main stem to promote branching. Keep soil moist especially during dry periods. Remove old flowers to promote blooming.