How to Grow Larkspur Black Knight

Larkspur Black Knight

Delphinium ajacis 'Black Knight'

flower

Black Knight is a dramatic annual larkspur cultivar prized for its deep, dark purple-black flowers arranged in dense spires. This tall variety reaches 3-4 feet and produces striking vertical blooms ideal for cut flowers and cottage gardens. The feathery foliage adds fine texture to garden beds and floral arrangements.

Looking for a specific variety?

Sky Blue Exquisite Pink White King Carmine Red Purple Splendor Salmon Beauty

Growing Conditions

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Sun: Full sun, 6-8 hours daily; tolerates partial afternoon shade in hot climates

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Water: Moderate watering; keep soil consistently moist but not waterlogged. Water at the base to avoid fungal issues on foliage. Reduce watering once established.

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Spacing: 12 inches

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Days to maturity: 50-60 days from transplant to first bloom; 70-90 days from seed

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Planting depth: Press seeds onto soil surface; they need light to germinate. Do not cover. For transplants, plant at soil level.

Soil

Type: Well-draining loamy soil with good structure

pH: 6.0-7.0

Amendments:

Compost or aged manure for organic matter Perlite or sand for drainage if soil is clay-heavy

Growing Zones

Find your zone →

Thrives best in zones 2-8; can be grown in zone 9 with afternoon shade and extra water

2a 2b 3a 3b 4a 4b 5a 5b 6a 6b 7a 7b 8a 8b 9a

Growth Stages

Seed Germination & Seedling

10-14 days for germination; 4-6 weeks before transplanting size

Tiny seedlings emerge with cotyledons and fine, feathery first true leaves. Plants are delicate and slow-growing in early stages.

Provide bright light immediately to prevent leggy seedlings. Keep soil moist but not soggy to avoid damping off. Thin seedlings to 2-3 inches apart. Start seeds 6-8 weeks before last frost indoors.

Vegetative Growth

3-4 weeks after transplanting

Plants develop multiple stems and increasingly lacy, deeply lobed foliage. Height increases rapidly; plants reach 12-18 inches before flowering begins.

Harden off seedlings over 7-10 days before transplanting outdoors after last frost. Space 12 inches apart. Install stakes or supports early to prevent wind damage. Pinch tops at 6 inches to encourage branching if desired, though this delays flowering.

Flower Spike Formation & Blooming

4-6 weeks of active flowering

Tall central flower spikes emerge bearing densely packed dark purple-black florets. Plants reach full 3-4 foot height with multiple flowers opening progressively from bottom to top.

Provide sturdy support structures or stakes as plants grow taller. Deadhead spent lower flowers to encourage continued blooming. Water deeply but allow soil to dry slightly between waterings. Avoid wetting foliage to reduce powdery mildew risk.

Peak Bloom & Maintenance

2-4 weeks depending on climate

Plants are at maximum height and bloom density with multiple flower spikes in full color. Foliage may show stress in intense heat or humidity.

Continue deadheading for prolonged blooms. Provide afternoon shade in zones 8-9. Cut flowers regularly for arrangements to extend blooming season. Monitor for fungal diseases in humid conditions.

Seed Set & End of Season

Variable; through season end

If deadheading stops, flowers fade and seed pods develop along spike. Plants decline as temperatures rise or autumn approaches; foliage yellows and weakens.

Allow a few spikes to remain unharvested if seed collection is desired. Let plants dry in place to collect seeds, or pull and compost spent plants. No reseeding in most climates as larkspur is typically grown as annual.

Companion Planting

Plan your garden →

Plant with:

Salvia Yarrow Foxglove Roses Lavender Alliums White cosmos Bearded iris

Avoid planting near:

Cabbage Kale Broccoli (host to same pests) Fennel (allelopathic)

Common Pests

Spray with strong water jet or use neem oil. Encourage beneficial insects like ladybugs. Insecticidal soap for heavy infestations.
Increase humidity and water foliage regularly. Use miticides if severe. Remove heavily infested stems.
and
Hand-pick in early morning. Use copper barriers or diatomaceous earth. Beer traps for persistent infestations.
Improve air circulation; water at base only. Apply sulfur dust or fungicide at first sign. Remove heavily affected stems.
Ensure excellent drainage and avoid waterlogging. Remove and destroy affected plants. Do not replant larkspur in same location.

Uses

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Edible Flowers & Natural Dyes

Culinary

While technically edible in very small quantities, larkspur is more prized for its deep purple pigments used in natural plant dyes for textiles. The flowers contain anthocyanins that produce beautiful blue and purple hues. [source]

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Cut Flowers & Floral Arrangements

Craft

Black Knight larkspur is exceptional for cutting, prized by florists for tall dramatic spikes that add vertical interest and dark color to arrangements. The flowers dry well for dried arrangements and long-lasting displays. [source]

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Traditional Herbal Remedies

Medicinal

Historically, larkspur has been used in traditional folk medicine for skin conditions and parasitic treatments, though modern use is limited due to plant toxicity. The plant contains toxic alkaloids and should not be ingested without expert guidance. [source]

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Cottage Garden & Border Appeal

Household

Black Knight creates striking tall borders and focal points in cottage gardens, cutting gardens, and formal borders. The deep purple-black color provides strong visual impact and complements many other garden colors. [source]

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Pollinator Support

Wildlife

Larkspur flowers attract bees, hummingbirds, and other pollinators to the garden. The nectar-rich spikes provide valuable food sources, especially during midsummer when other flowers may be declining. [source]

This is not medical advice. LizPlants is not a medical resource. Always consult a qualified healthcare professional before using plants medicinally.

Harvest Tips

Cut flower spikes for arrangements when lower flowers are open and upper buds show color; they'll continue opening in the vase. Cut in early morning when stems are most turgid. Larkspur lasts 7-10 days in a vase. For seed collection, allow spikes to fully dry on plant in late summer, then collect by cutting spikes and storing in paper bags in cool, dry location.

Fun Facts

🌱 Larkspur gets its common name from the distinctive spur on the back of each flower that resembles a lark's claw or spur. The genus name Delphinium comes from the Greek word 'delphin' (dolphin) because the flower's shape resembles a dolphin.
🌱 Black Knight larkspur is toxic to humans and livestock if ingested due to alkaloid compounds, but it's safe to handle or cut for arrangements. Historically, larkspur extract was used as an insecticide for livestock.
🌱 Annual larkspurs like Black Knight are easier to grow than their perennial Delphinium cousins and have become modern cottage garden favorites. Unlike perennial delphiniums which require cool climates, annuals tolerate warmer zones and don't require division.

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