Delphinium produces tall showy spikes of brightly colored flowers in summer. Blooms come in a range of colors—blue, violet, pink, white, or two-toned.
The delphinium’s tall wand of flowers emerges from a low mound of foliage. Columns of blooms grow from 3 to 6 feet (.9-1.8m) tall or more. Leaves are lobed or fanlike and variously cut or divided.
Delphiniums grow best where nights are cool and days are warm. Delphiniums appreciate shade during the middle of the day. Delphinium does not tolerate wind, heat, drought, or poorly drained soil.
Delphiniums are an excellent choice for borders and cut flowers. Low-growing types are well-suited for containers. Delphinium flowers attract all types of birds to the garden.
The annual delphinium is larkspur; see Consolida ambigua.
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Get to know Delphinium
- Plant type: Perennial
- Growing zones and range: Grow as an annual in Zones 2 to 7; grow as a perennial in Zones 6 to 7 where summers are cool.
- Hardiness: Hardy to -35°F (-37°C); good choice in cool summer regions, not suited for hot regions
- Height and width: 3 to 7 feet (0.9-2.1m) tall; 1 to 3 wide (.3-.9m)
- Foliage: Basal leaves are toothed and deeply or shallowly lobed to 8 inches (20cm) long
- Flowers: Flower spikes are 12 to 15 inches (30-38cm) long; single flowers are 2 inches (5cm) wide.
- Flower color: Intensely blue flower spikes, also light blue, lavender, pink, purple, red, and white
- Bloom time: Early summer
- Uses: Good addition to mixed borders
- Garden companions: Shasta daisy, veronica, sunflower, Joe-Pye weed, anise, hyssop, fragrant bugbane, ornamental grasses.
- Common name: Delphinium
- Botanical name: Delphinium elatum
- Family: Ranunculaceae
- Origin: Mountainous areas worldwide
Where to plant Delphinium
- Grow delphiniums in full sun to partial shade.
- Plant delphiniums in humus-rich, moist, well-drained soil.
- Delphiniums grow best where the soil pH is 6.5 to 7.5.
- Delphiniums thrive in regions with cool summers; in hot summer regions; plant delphiniums where there is morning sun and partial shade in the afternoon.
- Plant delphiniums where there is good air circulation to help prevent disease.
Delphinium uses and companions
- Grow Delphinium at the back of formal gardens.
- Delphiniums are traditional cottage garden plants along fences.
- Del[hiniums combine well with iris, peonies, daylilies, Shasta daisies, and lilies.
- Good garden companions for Delphinium include Chrysanthemum superbum, Heliopsis helianthoides, Hemerocallis, Monarda, Iris (Siberian).
When to plant Delphinium
- Set established plants in the garden in spring or autumn.
- Start seeds indoors in early spring or late summer (for bloom the following year). Sow seeds on the surface of pre-moistened soil. At 60°F (15.6°F) germination will occur in 2 to 4 weeks. Harden seedlings off for 2 weeks before setting them in the garden.
- Sow seeds in prepared beds in early spring or late summer.
- Container-grown plants can be set in the garden in spring or fall.
Planting and spacing Delphinium
- Space delphiniums 1 to 3 feet (30-91cm) apart.
- Dig in compost and well-rotted manure at planting time; grade the soil so that it will not collect water.
- Set transplants in the garden so that roots are securely covered with soil.
How to water and feed Delphinium
- Keep the soil evenly moist when growing delphiniums. Do not let the soil dry out. Avoid wetting the leaves when watering.
- Constantly wet soil leads to crown rot and death.
- Fertilize delphiniums every 6 to 8 weeks with an all-purpose fertilizer.
- Mulch around delphiniums to conserve soil moisture.
- Delphinium is prone to disease where summers are warm.
- Stake delphiniums when they reach 18 inches (45cm) tall. Use stakes as tall as the plants are expected to grow; tie flowering spikes to stakes. Cut off flowers just below the lowest flower; new growth will begin from the plant’s base.
- Remove spent flowers to encourage new blooms.
- Protect plants in winter by spreading a 3-inch layer of clean sand over the plants in late fall, or cover crowns with evergreen branches.
Delphinium pests and diseases
- Delphiniums are susceptible to attack by mildew, slugs, and snails.
- Aphids can infest young leaves and flower buds. Earwigs can damage flowers.
- Powdery mildew and fungal diseases can affect the leaves; plant delphiniums where there is ample air circulation.
- Crown rot can be a problem where the soil stays wet.
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- Propagate delphiniums by sowing seeds or cuttings.
- Seeds germinate in 21 to 28 days at 70° to 75°F (21-24°C).
- Take cuttings from shoots at the base of the plant in early spring; each cutting should have a sliver of the crown attached,
- Divide established plants every 4 years in early spring. Use a sharp knife to cut tangled roots.
- Propagate delphiniums from plant divisions frequently; delphiniums begin to decline after their second year.
- Handle the plants with care; the roots are brittle and break easily.
Delphinium varieties to grow
- Delphinium ajacis. See Consolida ambigua, larkspur, or rocket larkspur.
- Delphinium belladonna: bushy perennial with short-stemmed, airy flower clusters; easy to grow; shorter than D. elatum. D. belladonna has parented many hybrids, some grow to 4 feet tall (1.2m) tall; blooms have prominent spurs.
- Delphinium elatum: almost all delphiniums are hybrids of Delphinium elatum including Pacific hybrids which are considered the most spectacular; Pacific hybrids grow to 7 feet (2.1m) tall, included are ‘Blue Bird’ (mid blue), ‘Blue Jay’ (medium to dark blue), ‘Summer Skies’ Ilight blue). Other D. elatum hybrids include Blue Fountains and Magic Fountains; strains include lilac-pink, deep raspberry rose, lilac, lavender, royal purple, and dark violet. The Arthurian Round Table series includes ‘Astolat’ (lilac blue), ‘Black Knight (violet-black), ‘Galahad’ (white), ‘Percival (white and black), ‘King Arthur’ (violet).
- D. grandiflorum, Chinese or bouquet delphinium: bushy to 12 inches (30cm) tall; upward-facing blue flowers.
Delphinium x elatum — Delphinium
Delphinium x elatum is a perennial that bears striking tall spires of flowers in summer. Blossoms begin to unfold at the bottoms of the spires. Flowers are rounded in outline and spurred; often a central small ring of petals rests among the outer petals, creating a so-called “bee” in a contrasting color. Flowers are so dense that they may topple the plant from its own weight if not staked. Delphiniums have boldly cut, maplelike leaves in dark green clumps.
Classic delphiniums grow as high as 7 feet, but shorter strains are easier to grow and more durable during foul weather. Colors are cool; alluring shades of true blue, lavender, purple, pink, white, and bicolored, including pastels and intensely saturated hues. Plants are usually short-lived, surviving five years in the Pacific Northwest and Northeast and only two or three years elsewhere.
- Size: 3 to 7 feet tall; 1 to 3 feet wide, depending on cultivar.
- Light: Full sun in most climates; light shade in hottest areas, where adapted.
- Soil and moisture: Fertile, deep, alkaline soil rich in organic matter; keep evenly moist with ample water.
- Planting and propagation: Plant container-grown plants in spring, taking care to place the crown at soil level because planting too deeply causes crown rot. Space tall types 3 feet apart. Divide every other year for best longevity, or take cuttings from commercial seed. In areas with hot summers or mild winters, plant in fall and remove after flowering finishes in summer.
- Special care: Thin young plants to three shoots when 6 inches tall, mature plants to four or five shoots. Tall types must be individually staked, beginning when 1 foot tall, to prevent brittle stems from breaking. Plant in a location sheltered from wind. Fertilize monthly during bloom season. Mulch heavily to keep the soil cool. For repeat blooms, cut spent flower spikes just below the lowest blossom; when new growth is 6 inches tall, remove the spent flower stalk at the ground.
- Pests and diseases: Slugs, snails, mites, and mildew can be very troublesome; a regular pest control program is advisable.
- Climate: Zones 2-7. Best where summers are moist and cool to warm-not hot-and winters are cold.
- Cultivars and similar species: Mild-century hybrids, mildew resistant, 4 to 5 feet tall, ‘Ivory Towers,’ white; ‘Moody Blues,’ light blue; ‘Rose Future,’ pink; ‘Ultra Violet,’ dark blue-violet; ‘Magic Fountains,’ mixed colors, dwarf to 3 feet tall. Pacific Hybrids, 4 to 5 feet tall; huge single to semi-double flowers. ‘Black Knight,’ deep violet with black eye; ‘Astolat,’ lavender to pink with dark eye; ‘Blue Bird,’ mid-blue with white eye; ‘Galahad,’ all white; ‘Summer Skies,’ sky blue with white eye. Blackmore and Langdon hybrids, mixed colors with extremely large flower spikes. Connecticut Yankee strain, heavily branched 2 ½ to 3 ½ feet tall, similar to D. x belladonna; ‘Blue Fountains,’ blue, white, or mauve, Zones 3-8. D. x belladonna (belladonna delphinium): 2 to 3 feet tall, branched stems with central branch blooming first, many cultivars. D. grandiflorum (Chinese delphinium): finely divided leaves, 1 to 2 feet tall, loose spires of blue, violet, or white single, spurred flowers, Zones 3-7; ‘Blue Butterfly,’ vivid deep blue, 1 foot tall, long blooming; ‘Album,’ white.
- Garden use: Elegant and almost essential in the back of a formal garden. Also traditional along fences in cottage gardens. Combines well with iris, peonies, daylilies, Shasta daisies, and lilies.
Delphinium frequently asked questions
Q: What’s the best way to germinate delphinium seed?
A: Start with fresh seed every year–delphinium seeds are short-lived. Be sure to cover the seeds; they need darkness to germinate. You can start seeds indoors 6 to 8 weeks before the first frost, but be careful when it comes time to transplant them, they do not like their roots being disturbed.. Set plants in the garden 1 to 2 weeks after the last frost.
Q: When should I sow delphinium directly in the garden?
A: Sow delphinium in the garden as soon as the soil can be worked in spring about 4 or 5 weeks before the last frost. Delphiniums prefer cool weather. Grow delphinium in well-drained, moderately fertile, alkaline soil in full sun or light shade.
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