1000 Seeds Delphinium Seed Giant Imperial Mix Striking Mixed Colors A popular mix for cutting or landscaping.. Grows about 36 tall. Annual. Delphinium is a stately, elegant perennial that is a standard in English cottage gardens. Mounds of dark green, glossy foliage are adorned with huge spikes of showy, spurred flowers in early summer. Another common name is larkspur, although this name usually refers to annual varieties. Delphiniums thrive in regions with relatively cool and moist summers, and often struggle in hot, dry summer weather. However, some new varieties are more tolerant of heat. Delphiniums are available in a range of sizes, from dwarf varieties less than 2 feet tall to those with towering, 6-foot blooms. Flower color includes blue, red, white, and yellow; however, the rich, clear blues are especially prized by many gardeners. The plants bloom in late spring to early summer, and the flowers are suitable for cutting.