Delphinium, commonly known as Larkspur, is a genus of about 300 species. Delphiniums are widely known for their showy spikes, strong stems and beautiful blue flowers. Delphiniums come in several colors, including blue, red, pink, white, violet, and yellow, but blue is the most common. The flower spikes can reach 30 cm to 180 cm (1 to 6 ft) tall. The plant grows best in moist, but well drained soil. The pH of the soil should be neutral to slightly alkaline.