Delphinium (larkspur)
Delphinium spp.
Tall, showy herbaceous perennials with spiked, colorful flowers (larkspurs). Prefer cool summers, rich well-drained soil, full sun to part shade, regular moisture, and often need staking.
Caution: Toxic to Pets
Toxicity: highly toxic
All plant parts contain toxic diterpenoid alkaloids. Ingestion can cause vomiting, weakness, breathing and cardiac problems. Skin contact may cause irritation—wear gloves.
🌱Care Requirements
Light
Plant in full sun to light afternoon shade; in hot regions give bright, filtered light or morning sun with afternoon shade. Position near a sheltered, south- or east-facing area to maximize blooms and reduce wind damage.
Water
Keep soil consistently moist but not waterlogged. Water deeply when the top 2–3 cm of soil dries; pots need more frequent watering. Use well-draining compost, avoid standing water and water at the base to limit foliage wetting.
Humidity
Prefers average to medium humidity with good air circulation. Reduce disease risk by spacing plants, avoiding overcrowding, and mulching to retain steady soil moisture without raising air humidity.
Temperature
Best grown between 10–24°C (50–75°F); tolerates winter lows to about −20°C (−4°F) and brief heat up to 30°C (86°F). Avoid prolonged high heat.
🔧Common Problems & Solutions
Yellowing, wilting foliage
Cause: Poor drainage or root rot from overwatering
Solution: Improve drainage, reduce watering, remove affected tissue and replant in fresh, well-draining soil or raised bed.
Powdery mildew or leaf spots
Cause: High humidity, poor air circulation, or overhead watering
Solution: Increase spacing, water at soil level, remove infected leaves, use fungicide if severe and improve air flow.
Aphids and slugs on shoots and buds
Cause: Pest infestation attracted to tender growth
Solution: Hand-pick slugs, set traps, blast aphids with water or use insecticidal soap/biocontrols; encourage predators.
Stem breakage or floppy spikes
Cause: Tall flower spikes unsupported or weakened by wind/rain
Solution: Stake tall varieties early, plant in sheltered site, deadhead spent flowers to encourage basal growth.
✂️How to Propagate Delphinium (larkspur)
Seed: sow fresh or stratified seeds in autumn or early spring on surface or lightly covered; keep cool and moist until germination. Division: lift crowns in spring or autumn every 3–4 years; divide viable clumps with roots and replant at same depth. Stem cuttings: take basal or softwood cuttings after flowering, use rooting hormone and high humidity; root in free-draining mix.
🌍Origin & Background
Family: Ranunculaceae
Native to: Temperate regions of the Northern Hemisphere: Europe, central and northern Asia, and western North America.
Natural Habitat: Grows in cool, well-drained mountain meadows, open woodlands and rich soils with consistent moisture. Prefers sheltered, sunny to partly shaded sites with good air movement.
🗓Seasonal Care Guide
Winter
Cut back flowering stems after frost; leave some basal foliage for protection. Mulch over crowns in very cold or wet sites but avoid burying crowns completely.
Spring
Feed with balanced fertilizer when shoots emerge, divide clumps if needed, stake young spikes and ensure even moisture for robust growth.
Summer
Keep soil evenly moist, deadhead spent blooms to prolong flowering, protect from extreme heat and provide afternoon shade if temperatures rise.
Fall
Allow foliage to die back naturally, collect seeds if desired, divide overcrowded clumps and refresh soil with compost before winter.
❓Frequently Asked Questions
Do delphiniums come back every year?
Yes, most Delphinium species are perennial and will return; divide crowded clumps every few years to maintain vigor.
How tall do delphinium plants grow?
Height ranges widely by variety from 30 cm (12 in) to over 2 m (6+ ft); choose cultivars suited to your site and stake tall types.
Can I grow delphiniums in containers?
They can be grown in large, deep pots with rich, well-draining compost and regular watering, but flowering may be reduced.
When should I deadhead delphinium?
Deadhead spent flower spikes to encourage a second flush; cut flower stems down to a healthy leaf whorl.
Are delphiniums poisonous to pets?
Yes, they are highly toxic; keep pets away and plant with caution where animals may nibble foliage.
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Last updated: 11/7/2025