Cosmos bipinnatus 'Sonata White'
This compact white cosmos is part of the Sonata Series for small spaces and containers. It stands out for dwarf habit and clean white single blooms that show well up close. It performs best in full sun and average, well‑drained soils. Plants flower from summer to frost in most regions. Shorter stems make it easier to place at the front of borders. Treat it as a frost‑tender annual in North America.
At‑a‑glance
Group/Class: Sonata Series; annual cosmos
Height × spread: 12 to 16 in (30 to 40 cm) × 10 to 20 in (25 to 50 cm)
Bloom window: summer to frost
Color & flower form: pure white single daisies; about 3 in heads
Fragrance: 0 none
USDA hardiness: grown as annual in all zones; frost tender
Breeder / Year / Origin: unknown
Cut‑flower notes: shorter stems than tall types; harvest just as the first petals open; trials report vase life of about 5 to 8 days depending on conditions.
Pet safety: safe; generally non‑toxic to pets; ingestion may cause mild stomach upset.
How it differs
- Dwarf habit for containers and tight beds.
- Earlier and more even flowering than many tall strains.
- Shorter stems reduce lodging in wind.
- Pure white color reads clearly in small gardens.
Strengths
- Compact plants fit containers and front borders.
- Long blooming with regular deadheading.
- Attractive to pollinators.
- Low maintenance in average soils.
Care in one minute
- Give full sun and well‑drained soil with low to moderate fertility.
- Water to establish then water when the top inch is dry.
- Avoid high nitrogen fertilizers to keep plants floriferous.
- Pinch young plants once to encourage branching; deadhead spent blooms.
- Start indoors or direct sow after frost for continuous color.
Watch‑outs
- Stems are shorter for cutting than tall cultivars.
- Grey mold can develop in prolonged wet weather.
- Aphids may appear on soft growth.
- Over‑fertilizing can reduce bloom show.
Best uses (tags)
containers; borders; cutting; pollinators
Provenance note
RHS lists trade name ‘PAS1789’ for ‘Sonata White’ within the Sonata Series; breeder details are not publicly specified.
References
- Royal Horticultural Society – Cosmos bipinnatus ‘Sonata White’ (PAS1789)
- Royal Horticultural Society – Cosmos advice page
- NC State Extension – Cosmos bipinnatus profile
- Veterinary Partner (VIN) – Safe and toxic garden plant
Written by: Your Flowers Guide editorial team
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