Astra Blue
Astra Blue is a compact selection of Platycodon grandiflorus grown for its large, star-shaped blue flowers that open from balloon-like buds. It suits small borders and containers in full sun to light shade. Plants thrive in well-drained, fertile soil and regular moisture, and they dislike waterlogged sites. Chicago Botanic Garden trials recorded this cultivar as compact yet variable in size among seed strains. It flowers through mid to late summer in most North American gardens.
At‑a‑glance
Group/Class: Astra Series; dwarf selection
Height × spread: 8-22 in (20-55 cm) × 12-24 in (30-60 cm)
Bloom window: early July to early September
Color & flower form: violet-blue; single, star-shaped from balloon buds
Fragrance: 0 none
USDA hardiness: zones 3-8
Breeder / Year / Origin: unknown
Cut-flower notes: firm stems; sear cut ends at harvest to prevent sap bleed; holds when conditioned
Pet safety: unknown
How it differs
- Shorter and bushier than typical balloon flower.
- Earlier to bloom than many tall strains.
Seed-grown lines can vary in height and width.
Stems are more self-supporting in summer than taller types.
Strengths
- Compact habit for containers and edging.
- Long summer bloom with regular deadheading.
- Cold hardy into northern zones.
- Generally low pest and disease pressure.
Care in one minute
Site: full sun to light shade with wind exposure limited for taller stems.
Soil: deep, fertile, well-drained loam; slightly acidic to neutral pH.
Water: keep evenly moist; avoid soggy conditions.
Feeding: light spring feeding; excess nitrogen encourages flop.
Grooming: deadhead to extend bloom; cut stems back by half in late spring if height control is needed.
Overwintering: mulch lightly after frost; mark clumps because shoots emerge late.
Watch‑outs
- Seed strains may grow taller than listed.
- Stems can relax by early fall if grown in partial shade.
- Crowns resent disturbance once established.
Best uses (tags)
containers, edging, borders, cutting, rock gardens
Provenance note
The Astra line is a modern seed series selected for compact growth. Independent trials documented size variability in seed-grown plants.
References
- Chicago Botanic Garden – A Comparative Study of Platycodon grandiflorus Cultivars (2009)
- Missouri Botanical Garden – Platycodon grandiflorus (Plant Finder)
- NC State Extension – Platycodon grandiflorus profile
- RHS – Platycodon grandiflorus species profile
Written by: Your Flowers Guide editorial team
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