Although hybrid delphiniums (Delphinium spp.) do not grow well in most areas of North Carolina, some varieties are native to the state. These varieties are commonly called larkspur, because the spur the top of the flowers resembles a lark’s claw or spur. Hybrid and native delphiniums prefer cool weather and decline in hot, humid climates. Use hybrid and native delphiniums to add height and color to cottage gardens. Native delphiniums are also attractive in shaded areas or woodland gardens.
Hybrid delphiniums have large, showy blooms in shades of blue, violet and white during the summer. The plants grow 3 to 5 feet tall and have large lobed leaves. They need full sun and alkaline soil for the best growth and flowering. Hybrid delphiniums grow in U. S. Department of Agriculture plant hardiness zones 2 through 7. They only grow well in cool climates, such as the mountain regions of North Carolina. The plants lose their vigor and weaken after two to three years and need to be replaced with new plants.
Tall larkspur (Delphinium exaltatum) grows best in areas with cool summers, but it tolerates hot, humid weather better than hybrid delphiniums. It is hardy in USDA zones 5 through 7 and grows in the coastal, mountain and piedmont regions of North Carolina. It is taller than other native larkspurs -- up to 6 feet tall -- and grows 1 to 2 feet wide with dark green, lobed leaves. It blooms later than some other varieties in late summer through early fall with narrow, loose spikes of gentian blue flowers. It also has more foliage than other varieties. Tall larkspur grows in partial shade or sun but needs some afternoon shade in areas with hot summers. It prefers well-drained, fertile, alkaline soil.
Dwarf, or spring, larkspur (Delphinium tricorne) is a better choice for warm climates than other varieties of larkspur and is hardy in USDA zones 5 through 9. Although it grows in the coastal, mountain and piedmont areas of North Carolina, it does not grow abundantly. The long, open clusters of blue-violet, pink or white flowers appear in the spring before most other varieties of native larkspurs. It is shorter than other larkspurs and only grows 18 to 30 inches tall. It prefers rich, alkaline, well-drained soil in partial shade or full sun.
All parts of hybrid and native delphiniums are highly poisonous when ingested. The toxins burn the lips and mouth, and numb the throat. Other symptoms include intense vomiting and diarrhea, muscle spasms and weak pulse. Large doses lead to convulsions, paralysis of the respiratory system and possibly death.