Culture
Winter hardy to USDA Zones 3-7 where this delphinium is best grown in fertile, humus rich, medium moisture, well-drained soils in full sun. Performs well in alkaline soils. Appreciates some part afternoon shade in hot summer climates. Prefers climates with cool summer temperatures. Plants often struggle in St. Louis summers, and are generally not recommended for growing in hot and humid summer climates south of USDA Zone 7. Plants require protection from strong winds and rain storms via sheltered growing positions and staking. After bloom, promptly cut back spent flower spikes to the basal foliage to encourage an additional late summer and/or fall bloom. Straight species plants may be grown from seed and may self-seed in the garden,
Noteworthy Characteristics
Delphinium elatum, commonly known as delphinium, is an herbaceous perennial of the buttercup family that is native to clearings, woodland margins, and river valleys from southern and central Europe to Siberia. Species plants have been cultivated since 1578. Spicate flowering stems to 3-5’ tall are topped in late spring to early summer with erect, terminal, often spectacular, central flower spikes (racemes) which are densely packed with showy blue florets (25-100 per raceme). Each floret (to 1” across) has 5 blunt, glabrous, petal-like, blue outer sepals (posterior one is spurred) and two pairs of smaller true petals, with the lower two petals being yellow-bearded. The central raceme is surrounded by a number of smaller secondary flowering racemes (sidespikes) which develop from leaf joints below the primary bloom. Palmately lobed green leaves are 5-7 parted near the base.
Straight species plants are uncommonly sold in commerce today, however, because they have been largely replaced by a significant number of hybrid cultivars (typically designated as Delphinium x elatum or simply assigned to the Delphinium elatum group) which are generally considered to be of superior flowering quality (taller stems to 7-8’, larger and more floriferous flower spikes, and greater variety of flower colors).
Genus name comes from the Greek word delphis meaning dolphin in reference to the flower bud shape of some species purportedly resembling a dolphin.
Specific epithet comes from the Latin word elatus meaning tall.
Common name of bee delphinium is in reference to the configuration of throat petals.
Problems
Delphiniums require considerable maintenance (staking, pruning, deadheading, disease control) in order to perform well in the garden. Delphiniums are generally susceptible to powdery mildew, botrytis blight, leaf spots and crown rot. Plants grown in full sun generally show better resistance to powdery mildew. Water plants at the base to avoid wetting the foliage. Crown rot will inevitably develop if plants are grown in poorly drained soils or planted too deep. Slugs and snails can do significant damage. Watch for aphids, leaf miners, stem borers and mites. Taller plants may need staking and appreciate being sited in locations protected from wind. Plants are considered toxic to humans if ingested.
Uses
Superb in cottage gardens. Back of beds and borders. Best in groupings or massed. Plant against a stockade fence for protection from wind. Excellent cut flower. Deer and rabbits usually do not cause problems.