Often associated with the grand borders of England, stately delphiniums are problematic in most of the South. Those fancy hybrids (such as D. elatum hybrids) can't take our long, hot, humid summers and seldom last more than a year or two; in fact, they're best treated as annuals. Native species may be less spectacular than the hybrids, but they are reliably perennial, rising up in the garden year after year.
Bloom typically comes from spring to early summer. Cool blue is the classicand probably the favoritecolor, but delphiniums are also available in white, yellow, pink, lavender, purple, and red. Leaves are lobed and fanlike, variously cut and divided. All delphiniums are effective in borders and make good cut flowers; lower-growing types do well in containers. The blossoms attract birds. For annual delphinium (larkspur), see Consolida ajacis.
D.belladonna. Zones US, MS; USDA 6-7. To 34 ft. tall, 2 ft. wide. Sturdy, bushy plant with deeply cut leaves and short-stemmed, airy flower clusters. Selections include light blue 'Belladonna', dark blue 'Bellamosum', white 'Casa Blanca', and deep turquoise blue 'Cliveden Beauty'. All have 1- to 2-in.-wide flowers and are longer lived than tall hybrids listed under D. elatum.
D. carolinianum. CAROLINA LARKSPUR. Zones US, MS, LS; USDA 6-8. Native to the Southeast, southern Midwest, Texas. Narrow plant (just 6 in. wide at base) bears erect, 1- to 3-ft. spikes of blue or white flowers. Blooms heavily in spring, then goes dormant in summer. Reseeds readily and tolerates just about any well-drained soil.
D. elatum. CANDLE DELPHINIUM. Zones US; USDA 6, elsewhere as an annual. Siberian species to 36 ft. tall and 2 ft. wide, with small dark or dull purple owers. Along with D.cheilanthum and others, it is a parent of modern tall-growing delphinium strains.
Pacic strain hybrids (also called Giant Pacic, Pacic hybrids, and Pacic Coast hybrids) grow to 8 ft. tall. They are available in selected color series; members of these include 'Blue Bird', medium blue; 'Blue Jay', medium to dark blue; 'Galahad', white with white center; 'Percival', white with black center; 'Summer Skies', light blue. Other purple, lavender, pink named selections are sold.
Like Pacic strain but shorter (22 ft. tall) are the Blue Fountains, Blue Springs, and Magic Fountains strains. Even shorter is the Stand Up strain (1520 in.). These shorter strains seldom require staking.
Centurion is a long-stalked (45 ft. tall), large-flowered hybrid strain similar to the Pacific strain. It too will bloom the first year from seed, but it's more reliably perennial. New Millennium hybrids come in a range of heights and colors and were bred for heat tolerance and mildew resistance.
Other strains have owers in shades of lilac-pink to deep raspberry-rose, clear lilac, lavender, royal purple, and darkest violet.
D. exaltatum. TALL LARKSPUR. Zones US, MS, LS; USDA 6-8. Native to moist woods from Pennsylvania and Ohio south to North Carolina and Alabama. Showy true blue flowers appear on spikes 36 ft. tall in summer; plants reach 12 ft. wide. Best in light shade but blooms even in full shade. Tolerates drought once established.
D. grandiorum (D. chinense). CHINESE DELPHINIUM, BOUQUET DELPHINIUM. Short-lived perennial treated as biennial or annual. Zones US, MS, LS, CS, TS; USDA 6-11. Native to Siberia and eastern Asia. Bushy, branching, 1 ft. tall or less. Selections include 'Dwarf Blue Mirror', 1 ft., upward-facing, deep blue owers; and 'Tom Thumb', 8 in. tall, pure gentian-blue owers.
Delphiniums are easy to grow from seed. In the Middle, Lower, and Coastal South, sow fresh seed in flats or pots filled with potting soil in July or August; set out transplants in October for bloom in late spring and early summer. In the Upper South, sow seed in March or April, and set out transplants in June or July for first bloom by September (and more bloom the following spring).
Plants need rich, porous soil and regular feeding. Improve poor or heavy soils by working in lots of organic matter. Add lime to strongly acid soils. Work a handful of superphosphate into the soil around the root ball. Be careful not to bury the plant's root crown.
When new stalks appear in spring, remove all but the strongest two or three, tie to stakes, and apply a bloom-booster fertilizer. After blooms fade, cut stalks nearly to the ground, leaving foliage at the bottom. Fertilize again, and you may get a second bloom.