Cosmos
Cosmos bipinnatus (garden cosmos); some listed varieties are sulphur cosmos (C. sulphureus) or chocolate cosmos (C. atrosanguineus) · Daisy family (Asteraceae)
| Hardiness zones | 2 to 11 |
|---|---|
| Sun | full sun |
| Water | low |
| Life cycle | annual |
| Frost | Tender: killed by frost |
| Soil pH | 6.0–8.0 |
| Spacing | 12 to 36 inches |
| Soil temperature to plant | at least 65°F |
About Cosmos
Garden cosmos is an easy, airy annual with daisy-like flowers in pink, white and magenta on 2- to 4-foot plants. It blooms all summer, draws pollinators and birds, and often reseeds itself.
Grown as a summer annual in every zone (NC State lists 2-11); frost kills it.
When to plant
Timing is counted from your average last spring frost (and first fall frost). Sow & Tell works out the actual dates for your ZIP code.
- Sow seeds outdoors: up to 2 weeks after the last frost
Sow seed outdoors after frost once the soil reaches about 65 F; seedlings appear in 7-21 days (NC State). Tall varieties may need staking in windy spots.
Soil
Well-drained soil of almost any texture; it tolerates dry spells.
Plant in well-drained soil of average to poor fertility with a neutral to slightly alkaline pH; just loosen the soil and rake out weeds before sowing. Do not add compost or fertilizer.
Feeding
Do not fertilize cosmos: extra nutrients give weak stems, later bloom and fewer flowers.
Harvest
Deadhead spent flowers to keep more coming, or leave some to reseed (NC State).
Varieties (18)
| Variety | Type | Days | Notes |
|---|---|---|---|
| Antiquity | Garden cosmos (C. bipinnatus) | Short, 1-2 ft plants that bloom early; 2-inch flowers. | |
| Candy Stripe mix | Garden cosmos (C. bipinnatus) | White flowers striped along the petals. | |
| Chocolate | Chocolate cosmos (C. atrosanguineus), a different species | Deep maroon, chocolate-scented flowers; uncommon. | |
| Daydream | Garden cosmos (C. bipinnatus) | Pale pink petals that darken toward the center. | |
| Early Wonder | Garden cosmos (C. bipinnatus) | White or pink flowers. | |
| Gazebo mix | Garden cosmos (C. bipinnatus) | White, pink and red flowers on 3-4 ft plants. | |
| Picotee | Garden cosmos (C. bipinnatus) | White petals edged and streaked with reddish pink, around yellow centers. | |
| Psyche mix | Garden cosmos (C. bipinnatus) | Tall, 4-5 ft plants with lavender-pink or white flowers. | |
| Purity | Garden cosmos (C. bipinnatus) | White flowers. | |
| Seashells mix | Garden cosmos (C. bipinnatus) | Petals rolled into tubes, in red, pink and white; about 3 ft tall. | |
| Sensation series | Garden cosmos (C. bipinnatus) | Large flowers in pink, red and white. | |
| Sonata series | Garden cosmos (C. bipinnatus) | Compact, 1-2 ft plants with large pink, white or red flowers. | |
| Versailles series | Garden cosmos (C. bipinnatus) | Large red, white or pink flowers bred for cutting. | |
| Bright Lights | Sulphur cosmos (C. sulphureus) | A sulphur cosmos selection listed by NC State. | |
| Cosmic series | Sulphur cosmos (C. sulphureus) | Compact, 12-18 inch plants with 2-inch double and semi-double flowers in orange, red and yellow that hold their color. | |
| Lemon Twist | Sulphur cosmos (C. sulphureus) | A sulphur cosmos selection listed by NC State. | |
| Sunny Gold | Sulphur cosmos (C. sulphureus) | A sulphur cosmos selection listed by NC State. | |
| Sunny Red | Sulphur cosmos (C. sulphureus) | A sulphur cosmos selection listed by NC State. |
Pests to watch for
Aphids
Diseases and problems
Powdery mildew, Gray mold (Botrytis)
In the kitchen
Pets: Not listed as toxic by the ASPCA
Sources
Photo: Photo: Ronincmc, CC BY-SA 4.0, via Wikimedia Commons (CC BY-SA 4.0). Photo resized for the web.
Planting dates and advice are general guidance; check with your local Cooperative Extension office for your area.