Hardy perennial and annual plants of varying heights which bloom in June and July chiefly; the original species or wild types from which the modern beautiful varieties are descended are natives of California, Siberia, Syria, India and other countries. Delphinium Ajacis, originally from eastern Europe is one of the plants from which the annual Larkspurs have been raised. Delphinium belongs to the Buttercup family, Ranunculaceae. The name is an old Greek one.
Numerous beautiful named varieties of the perennial Delphinium have been raised in Europe and are there propagated vegetatively, but in North America Delphiniums are not commonly long-lived and it is customary to propagate by seeds and to raise fresh stocks frequently. Good strains of seed give a high percentage of magnificent flowers. Delphiniums thrive best where summers are cool.
The varieties with pale blue or bright blue flowers are the chief favorites, but the color range has been extended and includes mauve, rose mauve, pink, lavender, purple and indigo. Some of the flowers are of two colors, for instance, blue and white, purple and mauve, blue and mauve, purple and blue. The newest type is characterized by immense spikes of large blooms and unusually vigorous growth. Although the chief flowering season of the perennial varieties is in June and early July, if the main spike is cut off when the flowers have faded, smaller, secondary shoots will prolong the display.
It is often advised that after the first flowering the plants should be cut down to the ground for the purpose of encouraging the development of a second crop of bloom in late summer. This, however, is not to be recommended; it is bound to weaken the plants, for it deprives them of their large leaves. ARead more on backyardgardener.com