Delphiniums: How to Grow Majestic Spikes of Blue, Pink, and Purple

Delphiniums are prized perennials grown for their dramatic spires of colorful summer flowers in stunning shades of blue, pink, white, and purple. They're cottage-garden classics and superb cutting-garden stars.

Delphiniums delight many gardeners but can challenge beginners. They thrive in moist, cool summers and struggle in hot, dry conditions. Sudden wind or heavy rain can damage their tall stems. Except for dwarf varieties, most delphiniums require staking.

Planting Delphiniums Successfully

• Grow in fertile, well-drained soil in full sun to light shade, sheltered from strong winds.
• Plant in spring. Prepare soil by mixing in 2–4 inches of compost.
• Delphiniums are notoriously difficult from seed; buy potted plants from a nursery.
• Dig a hole twice the container's diameter. Set the plant so the root ball's top is level with the soil surface.
• In spring, broadcast lime, wood ashes, or a mix over these alkaline-loving perennials.

Care for Towering Blooms

• Install supports by mid-spring or when plants reach 12 inches. Use twiggy brushwood for low growers; sturdy stakes for tall, large-flowered types.
• Keep soil consistently moist. Water during summer if rainfall is under 1 inch per week.
• For quality spikes, thin shoots at 3 inches: leave 2–3 shoots on young plants, 5–7 on established ones.
• Water freely during growth; apply balanced liquid fertilizer every 2–3 weeks.
• Deadhead by cutting spent spikes back to small flowering side shoots.
• After main bloom, cut flower stalks to the ground—smaller secondary stalks often develop and withstand light frosts.
• If dividing in spring, replant the new outer plants; discard the woody old center.

Pests and Diseases

• Vulnerable to slugs, snails, and cyclamen mites.
• Fungal issues: powdery mildew, Southern blight, bacterial/fungal spots, gray mold, crown/root rot, white rot, rust, white smut, leaf smut, damping off.

Harvest and Storage

• Excellent for cutting gardens. Cut blooms as they open to encourage rebloom.
• Extend vase life with sugar, lemon juice, and bleach, or commercial floral preservative.

Recommended Varieties

Delphiniums range from dwarf to towering 6+ feet. Key groups:

• Belladonna Group: Upright, branching perennials with single flowers, 3–4 ft tall. 'Blue Bees' offers clear blue blooms with white centers.
• Elatum Group: Tallest hybrids, 6+ ft. 'Blue Nile' (medium, semi-double mid-blue with white bees); 'Bruce' (tall, semi-double violet-purple with brown bees).
• Pacific Hybrids: Similar to Elatum but shorter-lived, often grown as annuals/biennials. 'King Arthur' bears plum flowers with white bees on 5–6 ft spikes.

Wit & Wisdom

• Caution: Very young delphinium plants and seeds are poisonous. Ingestion can cause nausea, muscle twitching, paralysis, and even death.