How to Grow Larkspur
'Giant Imperial Mix' from Seed
The cut flower workhorse -- fully double branching spires of violet, deep blue, rose pink, carmine, and white on plants reaching 1.2m from an autumn sowing; the Imperial branching habit produces 8-12 cutting stems per plant rather than a single spike; a Hardy Annual cool-season specialist; pre-chill seeds 7 days; direct sow; cover for darkness; autumn sowing produces the tallest, most productive plants; dries beautifully for winter arrangements and biodegradable confetti
Larkspur 'Giant Imperial Mix' is the cut flower workhorse of the larkspur family -- a superior florist-quality strain that produces the quality of vertical height and flower density that makes larkspur irreplaceable in the cutting garden. Unlike older single-stem larkspur varieties, the 'Imperial' group branches from the base, giving each plant multiple flowering stems of varying heights. A well-grown autumn-sown plant can produce 8-12 individual cutting stems ranging from 60-120cm, providing weeks of continuous harvest as successive stems come into flower from the base upward. The fully double, ruffled flowers are packed in a romantic mix of violet, deep blue, rose pink, carmine, and white.
The autumn sowing advantage is dramatic for this variety. Autumn-sown Giant Imperial plants, grown with deep root systems through winter, regularly reach 120cm in height -- genuine Delphinium-scale verticals from a direct-sown annual. Spring-sown plants grow to 60-90cm. The difference in cutting stem quality between autumn-sown and spring-sown plants is significant enough that serious cut flower growers typically commit to the September sowing and the slightly more complex timing that involves. The dried stems are also exceptional -- Giant Imperial dried larkspur is used in wedding arrangements, winter wreaths, and dried bouquets worldwide, including as biodegradable confetti.
Quick Facts at a Glance
Plant Type
Hardy Annual H3 -- cool-season specialist; sow autumn (Sep) or spring (Mar-Apr)
Flowers
Fully double branching spires; violet, deep blue, rose pink, carmine, white; Jun-Aug
Form
BRANCHING from base -- multiple cutting stems per plant; cut flower workhorse
Height
Up to 1.2m from autumn sowing; the tallest larkspur strain
Key rules
Fridge trick 7 days; direct sow; darkness to germinate; toxic all parts
Difficulty
2 out of 5 -- fridge trick, direct sow, autumn for tallest
Understanding the Branching Imperial Form
Branching from the Base -- Multiple Cutting Stems
The Imperial improvement over older larkspur strains is the branching habit. Traditional single-stem larkspurs produce one central spike per plant -- beautiful but limited in cutting output. The Imperial strain branches strongly from nodes at the base of the plant, each branch developing its own flowering stem. The result is a more complex plant structure that looks more abundant in the border and provides significantly more cutting material per plant. For a dedicated cutting garden, Giant Imperial is the highest-volume larkspur choice.
The Fridge Trick and Autumn Timing
As with all larkspur varieties, pre-chill seeds in the fridge for 7 days before sowing to break dormancy. Direct sow in September for flowering in June and plants reaching 120cm. Direct sow in March-April for flowering in July-August and plants at 60-90cm. Both timings produce excellent plants; the September timing produces the most impressive. In both cases, cover seeds 3-5mm deep -- darkness is required for germination. Never transplant larkspur -- the taproot resents disturbance.
Toxicity -- All Parts Toxic if Ingested
All parts of larkspur (Consolida ajacis) are toxic if ingested by humans or animals. Wash hands after handling seeds or plants.
Sowing & Growing On
Pre-Chill 7 Days, Direct Sow in September for Maximum Height
For the tallest, most branched, most productive Giant Imperial plants, sow directly into the final position in September after pre-chilling seeds for 7 days in the fridge. Cover 3-5mm deep for darkness. Germination 14-21 days in cool autumn soil. Thin to 20-25cm to allow full branching development.
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Pre-chill seeds for 7 days in fridge or freezer before sowing. Sow directly in the final position in September (best, produces 120cm plants flowering June) or March-April (produces 60-90cm plants flowering July-August). Cover 3-5mm deep. Germination 14-21 days in cool conditions.
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Thin to 20-25cm when seedlings are 5-8cm tall. Giant Imperial needs adequate spacing to allow its characteristic branching habit to develop fully. Overcrowded plants produce fewer, weaker branches and smaller flower spires than properly spaced ones.
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Support with twiggy pea sticks or netting at 20-30cm plant height. The multiple stems of Giant Imperial can splay outward in wind. Install support early -- before the plants reach 40cm. In a sheltered border where plants support each other, additional staking may not be needed.
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Cut stems when one-third of florets are open; hang in darkness for drying. Vase life 7-10 days. For drying, cut at the same stage and hang in small bunches upside-down in a dark, airy location. Biodegradable confetti: allow stems to fully dry, then crumble individual florets -- the petals are fully biodegradable and produce beautiful confetti with long-lasting colour.
Garden Use & Care
Cut Flower Excellence
Giant Imperial provides the most generous cutting output of all larkspur varieties: 8-12 stems per autumn-sown plant, in a colour range spanning violet through deep blue, rose pink, carmine, and white, from June onwards. Cut when one-third of florets are open and condition in deep water for 12 hours before arranging. The tall, branched stems provide the vertical element that anchors larger arrangements -- particularly effective with Ammi majus (frothy white filler), Gypsophila (mist-of-white lower filler), and Cosmos (large open faces providing contrast with the dense larkspur spires).
Biodegradable Confetti
Giant Imperial dried larkspur provides the most beautiful and most environmentally-responsible wedding confetti available from a garden. Once fully dried, the individual florets crumble easily from the stem, producing petals in violet, blue, pink, carmine, and white that are genuinely biodegradable, fade over time in outdoor conditions, and are safe for birds and wildlife. Dry the stems fully (3-4 weeks), then crumble over a tray. Store in paper bags in a dry, dark location until needed.
Vertical Structure in the Border
At 120cm from an autumn sowing, Giant Imperial provides genuine back-of-border architectural height comparable to a well-grown perennial Delphinium but from direct sowing of a hardy annual. The multiple branching stems create a more naturalistic, less regimented vertical effect than a single-spike plant -- the branches varying in height and reaching different levels simultaneously, creating the complex layered vertical that looks most convincing as a naturalistic cottage garden planting.
The Blue in the Palette
The "deep blue" component of the Giant Imperial mix is among the most saturated, genuinely blue flowers available as a UK hardy annual. Pure blue is rare in annual flowers; the Imperial deep blue is a genuine, non-purple, clear blue that provides the colour wheel complement to the oranges and reds of summer annuals. Even a single stem of deep blue Imperial larkspur in an arrangement of warm-toned flowers creates the cooling, sophisticating balance that blue uniquely provides.
Self-Seeding
Giant Imperial self-seeds freely in suitable conditions -- a well-established sowing allowed to set seed will produce self-sown plants the following autumn or spring. Self-sown Imperial plants typically demonstrate vigour equal to or greater than deliberately sown ones. Allow some plants to fully ripen their seed before the end of the season. The self-sown colony gradually expands and shifts over the years, finding its own preferred positions in the cutting garden or border.
Border Companions
The classic Giant Imperial companion from the Bishy range: Ammi majus provides the frothy white filler that makes the larkspur spires look more dramatic; Gypsophila (either variety) provides the misty lower filler; Cosmos Purity provides the large open white contrast faces that perfectly offset the dense flower spikes of the larkspur. These three companions -- Giant Imperial, Ammi, and Cosmos -- are the foundational trio of the romantic white-and-colour cottage garden cutting patch.
Sowing & Flowering Calendar
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
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| Sow autumn (Sep -- best) |
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| Sow spring (Mar-Apr) |
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| Flowers from autumn sow |
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| Flowers from spring sow |
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Common Problems & Solutions
| Problem | Likely Cause | What to Do |
|---|---|---|
| Poor germination | Not pre-chilled; too warm; seeds exposed to light | Pre-chill 7 days in fridge. Sow in cool conditions (autumn or early spring). Cover 3-5mm deep for darkness. Warm spring temperatures without pre-chilling produce very erratic germination. |
| Branching weak; few cutting stems | Overcrowded; spring sowing only | Thin to 20-25cm to allow full branching development. Autumn sowing produces significantly more branching and more cutting stems than spring sowing -- for maximum yield, commit to the September sowing. |
| Stems too short | Spring sowing; sown too late | Autumn (September) sowing produces 120cm plants; spring sowing 60-90cm. If tall stems are a priority, sow in September for the following summer. |
| Confetti not biodegrading as expected | Petals not fully dried | Ensure stems are fully dry before crumbling (3-4 weeks hanging). Partially dry petals have higher moisture content and break down less evenly. Fully dry petals crumble easily and biodegrade cleanly. |
Plant Specifications
Eight to twelve cutting stems per autumn-sown plant in violet, blue, pink, and white -- the cut flower larkspur that keeps giving
Pre-chill seeds for 7 days in the fridge. Direct sow in September for 120cm branching plants flowering in June. Cover 3-5mm deep for darkness. Thin to 20-25cm for full branching development. Cut when one-third of florets are open for vase use or drying. Crumble fully dry petals for biodegradable confetti. The florist-quality spires provide weeks of cutting material from each plant.
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