Does it really smell like chocolate?

Yes, the velvety petals release a rich, cocoa-like fragrance.

Can I leave it outside in winter?

Only in frost-free climates; otherwise, lift the tubers and store them in a cool, dry place.

Plant guide

Chocolate cosmos.

Cosmos atrosanguineus

Pronounced KOS-mos at-ro-san-GWIN-ee-us

Also known as black cosmos, chocolate cosmos

Chocolate Cosmos — Photo by Juan Cruzado Cortés (CC BY-SA) via iNaturalist

This unique perennial is famous for its deep maroon petals and distinct scent of dark chocolate. It thrives in warm climates and adds a rich, moody aesthetic to any garden bed. You will love how it attracts pollinators while serving as a conversation piece.

Another photo of Chocolate cosmos — Photo by Michel Langeveld (CC BY) via iNaturalist

At a glance

Care level: Moderate
Plant type: Perennial
Light: Full sun
Indoor light: Direct sun
Water: Every 3 to 7 days
Mature size: 2 to 3 feet
Growth rate: Medium
Hardiness: USDA 7 to 11
Bloom time: Mid summer to late autumn

Care

Plant in well draining soil and ensure it gets plenty of sunshine to encourage blooming. Watch for drooping leaves which indicate a need for water, but be careful not to let the roots sit in soggy soil. Deadhead spent flowers regularly to keep the plant producing new buds throughout the season.

Watering: Water when the top inch of soil feels dry to the touch.
Feeding: Apply a balanced liquid fertilizer once a month during the active growing season.
Pruning: Regularly remove faded blooms to encourage continuous flowering.
Repotting: Repot in the spring if the plant becomes root bound in its container.
Soil: Well draining, fertile loam
Soil pH: 6.0 to 7.5
Temperature: 5 to 30°C
Humidity: 40 to 60%
Drought tolerance: Moderate
Lifespan: Perennial, typically 3 to 5 years with proper tuber care.
Fragrance: Strong
Deer and rabbits: Moderate

Signs it needs repotting

Roots growing out of the drainage holes.
Water sitting on the surface for too long.
Plant growth slowing down significantly.

Safety

People: All parts of the plant are considered mildly toxic if ingested.
Pets: This plant is generally considered non toxic to cats and dogs.
Children: Keep this plant away from small children as ingestion of any part can cause stomach discomfort.
Contact allergens: Handling the foliage may cause mild skin irritation in sensitive individuals.
Airborne allergens: The pollen can trigger mild reactions in those with seasonal allergies.
Edibility: The plant is not considered edible and ingestion may cause digestive upset.

How to identify it

Deep maroon to chocolate brown petals
Dark green pinnate foliage
Distinct chocolate scent in warm sun
Daisy like flower heads
Slender branching stems

Height: 0.4 to 0.75m
Spread: 0.3 to 0.5m
Leaves: dark green, deciduous
Flowers: deep maroon, chocolate brown, 3 to 5cm

Problems to watch for

AphidsCommon
Powdery MildewCommon
Root RotUncommon
Slugs and SnailsUncommon

By symptom

Plant problems by symptom

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Growing it

Propagation: division, cuttings
When to plant: spring
Overwintering: In cold climates, dig up the tubers after the first frost kills the foliage. Clean off soil and store them in a box of dry peat or sand in a cool, dark, frost-free location until spring.
In containers: It thrives in containers, provided the pot is at least 30 centimeters wide and has excellent drainage.

Tuber Division

1. Carefully lift the clump of tubers in spring.
2. Gently pull the tubers apart ensuring each has a growing eye.
3. Replant immediately in well draining soil.

Plant these in groups of three to five to create a noticeable impact with their unique color and scent.

Grows well with

Salvia · They share similar water and sun requirements.
Lavender · The purple tones contrast beautifully with the dark maroon flowers.

Similar species

Garden Cosmos · It is a related species with similar foliage but much larger, brighter flowers.

Science

Family: Asteraceae
Genus: Cosmos
Order: Asterales
Class: Magnoliopsida
Native range: Mexico
Conservation: This species is extinct in the wild and only exists in cultivation.

It evolved in the high-altitude meadows of Mexico where it relied on tuber storage to survive seasonal dry periods.

Value to wildlife: nectar source
Pollinators: bees, butterflies
Uses: ornamental border, container plant, cut flower

Through the year

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Flowering

Fruiting

Foliage

Ecological indicators

Salinity: 2/9
Soil reaction: 6/9
Light: 7/9
Temperature: 6/9
Moisture: 5/9
Nutrients: 5/9

Taxonomy resolved against GBIF.

Questions people ask

Does it really smell like chocolate?: Yes, the velvety petals release a rich, cocoa-like fragrance.
Can I leave it outside in winter?: Only in frost-free climates; otherwise, lift the tubers and store them in a cool, dry place.

Where the name comes from

The genus name comes from the Greek word for order or beauty, while the species name refers to its dark, blood-red color.

Good to know

It is a tuberous perennial that produces fleshy roots.
The chocolate scent is most intense on warm, sunny afternoons.
It was introduced to the UK from Mexico in the early 19th century.

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This guide was generated with AI on September 26, 2026 and checked against GBIF taxonomy. It is general information, not horticultural or veterinary advice. Read about how we build these guides.