How to Grow Delphiniums
Delphinium
Delphiniums need a sunny, sheltered spot with rich, well-drained soil and reliable staking for their tall flower spikes. Protect emerging shoots from slugs in spring — this is the single most important task. Feed regularly through the growing season and cut back to ground level after the first flush to encourage a second flowering in late summer. In autumn, cut all growth to the ground and mulch the crowns.
Yearly Lifecycle
Care Essentials
Spring with a balanced fertiliser. Liquid feed fortnightly during the growing season.
Watch For
- Slugs and snails (especially on new growth)
- Powdery mildew
- Black blotch
- Delphinium moth
Companions
Roses, Phlox, Geraniums, Lupins
Track your Delphiniums care schedule — pruning, feeding, and seasonal tasks
Start planning freeCare Requirements
☀️ Light
Full sun in a sheltered position
Full sun is essential. Choose a sheltered spot out of strong winds which can snap the tall flower spikes.
💧 Watering
Keep moist in growth; avoid winter wet
Keep soil consistently moist during the growing season, especially while flower spikes are developing. Avoid waterlogging in winter.
🌱 Fertilizing
Spring feed plus fortnightly liquid feed
Apply a balanced fertiliser in spring and liquid feed fortnightly during active growth to fuel the tall, energy-hungry flower spikes.
✂️ Pruning
Cut back after first flush for a second bloom
Cut stems to the base after the first flowering flush to encourage a second bloom in late summer. Cut all growth to ground level in autumn.
🌿 Support
Stake early before spikes develop
Stake when plants reach about 30 cm tall, before heavy flower spikes develop. Use individual canes or grow-through rings.
🍂 Mulching
Mulch crowns in autumn for winter protection
Mulch crowns in autumn with compost or bark to protect over winter. Keep mulch slightly away from the crown to reduce rot risk.
Growing Tips
Defend against slugs
Emerging delphinium shoots in spring are irresistible to slugs. Use barriers, beer traps, or biological nematode controls from the moment growth appears.
Stake early
Insert supports when plants are about 30 cm tall, before the heavy flower spikes develop. Individual canes or grow-through rings both work well.
Cut back for a second flush
After the first flowers fade, cut stems right down to the base. Feed and water well, and a second, shorter flush of blooms often follows in late summer.
Feed through the season
Apply a balanced fertiliser in spring and liquid feed fortnightly during active growth to fuel the tall, energy-hungry flower spikes.
Pests & Diseases
Pest Slugs and Snails
Identification: Shredded or completely eaten young shoots at ground level; slime trails around the crown
- Apply biological nematode control (Phasmarhabditis hermaphrodita) in early spring before shoots emerge
- Use copper tape, beer traps, or grit barriers around the crown
- Apply ferric phosphate slug pellets around emerging shoots from late winter
Pest Delphinium Moth
Identification: Wilting stem tips; bore holes in stems with frass; caterpillars found inside hollow stems when split open
- Cut out and destroy affected stems
- Clear plant debris in autumn to remove overwintering sites
- No specific chemical treatment; remove affected stems promptly
Pest Aphids
Identification: Clusters of green or black aphids on flower buds and stem tips; sticky honeydew
- Blast off with a strong jet of water
- Encourage ladybirds and hoverflies
- Spray with a pyrethrin-based insecticide before flowers open
Disease Powdery Mildew Erysiphe aquilegiae
Symptoms: White powdery coating on leaves and stems; affected leaves may yellow and drop
Treatment: Remove badly affected leaves; improve air circulation by thinning crowded growth
Prevention: Ensure good spacing; water at the base rather than overhead; mulch to retain soil moisture
Disease Black Blotch Pseudomonas syringae pv. delphinii
Symptoms: Large, irregular black or dark brown blotches on leaves; leaves may yellow and die; spreads upward from lower foliage
Treatment: Remove and destroy affected leaves promptly; cut back all growth in autumn and clear debris
Prevention: Avoid overhead watering; ensure good air circulation; remove lower leaves that touch the ground
Disease Crown Rot
Symptoms: Soft, mushy crown at soil level; shoots fail to emerge or collapse shortly after; foul smell
Treatment: Remove and destroy affected plants; do not replant delphiniums in the same spot
Prevention: Ensure excellent drainage; avoid mulching directly against the crown; do not overwater
Popular Varieties
Black Knight, Blue Bird, King Arthur, Summer Skies, Galahad, Magic Fountains, Pacific Giants
Log Delphiniums in your garden — track growth, care, and harvests year after year
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