From the Greek dolphin, a dolphin, the flowerbuds having some resemblance to that sea creature (Ranunculaceae). Larkspur. The genus consists of annual, biennial and herbaceous perennial plants, mostly hardy and showy plants for border cultivation, with some dwarf species suitable for the rock garden.
Sow annual varieties in a sunny, open border in April where they are to flower, or in boxes of light soil under glass in March in a temperature of 55°F (13°C). Prick out seedlings when large enough to handle and transplant in the open in May.
Perennials should be planted out in the spring or autumn in beds of rich, deeply cultivated soil ; dwarf varieties are suitable for rock gardens. Feed with liquid manure in the early summer. Lift and replant every third year. Propagation of perennial varieties is by means of cuttings of young shoots in early spring, inserted in sandy soil in pots in a shaded propagating frame, or by seeds sown in the open ground in late spring or under glass in spring.
Fast-growing plants, delphiniums require a deeply-dug, rich soil with adequate drainage. A medium loam is preferable to a light sandy soil. Where the soil is light dig in deeply plenty of compost or old farmyard manure before planting and during the summer a mulch of garden compost is excellent. Nitrogenous fertilisers should be used with care as they may only result in producing weak stems. If the stems are cut back immediately after flowering a second crop of spikes may be produced, but these should only be encouraged with strong-growing varieties.. Adequate moisture will be required to produce this second crop during what may be hot, summer weather.
Slugs can be a menace with the tender young delphinium shoots, especially in the earlyRead more on backyardgardener.com