Delphinium ajaci. Sow Rocket Larkspur delphinium seeds in fall or in early spring, when some risk of frost is still possible. Stunning spires in shades of purple and blue grow up to 1.2m (4′) tall, attracting wild and domestic pollinators. Grow this southern European native in full sun or part shade, but keep soil relatively moist. This annual Delphinium produces copious seeds and will self sow from year to year. The seeds are easy to collect and share. Alternately, simply cut the seed heads down after the flowers have faded and avoid self sowing all together. Rocket Larkspur looks amazing when contrasted with yellow or orange flowers of a similar height. Try planting it near Black-Eyed Susan Rudbeckia.