Ornamental · Asteraceae
Chocolate Cosmos
Cosmos atrosanguineus
Deep maroon blooms that genuinely smell of dark chocolate, borne on a tender tuber you handle much as you would a dahlia.
Full sun
USDA 7–9
2–3 ft · 0.6–0.9 m
Overview
Chocolate cosmos lives up to its name on two counts: petals the shade of dark chocolate and a fragrance to match on a warm afternoon. A member of the daisy family native to Mexico, it grows from a compact tuber rather than fibrous roots. Nearly every plant on sale descends from one sterile clone, propagated by division across many generations.
Growth stays restrained, topping out at 2 to 3 feet (61 to 91 cm), with flowers held on slender stems above finely cut foliage. Blooming runs from early summer deep into fall, giving you a long stretch of color in a border or container. Cut a few stems for a vase and the chocolate scent travels indoors with them.
Handle it as a tender perennial. It returns each year only in mild regions, so where winters bite, the standard practice is to lift the tubers and keep them dry, exactly as you would dahlia tubers, then set them out again in spring.
Care
The short version: full sun, ordinary soil with free drainage, and a light hand with water. Let the top half of the soil dry between waterings, feed sparingly, and keep the tubers out of standing moisture.
Light
Site chocolate cosmos in full sun, where it receives direct light for the bulk of the day. That strong exposure is what deepens the flower color and keeps the slim stems compact instead of stretching and flopping.
Water
Water with restraint and let the top half of the soil dry before watering again. The plant copes well with dry to average moisture, but saturated ground rots the tubers quickly, so lean toward dry and never leave it standing wet.
Soil
Set it in average, well-drained soil of moderate fertility. Sharp drainage outweighs richness here, because the tubers cannot persist in heavy, waterlogged ground. Amend with grit or use a raised bed wherever your soil retains water.
Humidity
Normal outdoor humidity suits it well, so there is no target to aim for. Air movement matters more, since crowded, motionless conditions are what allow powdery mildew to establish on the leaves.
Feeding
A light feed across the growing season covers its needs in full. Overfeed and you trade flowers for leafy growth, so keep it modest and let the plant channel its energy into blooms.
Pruning
Deadhead the faded flowers as they go over and the plant continues setting new buds for longer. Trim out any damaged or diseased growth as soon as you notice it to keep the plant healthy.
Size & spacing
Plan for a plant 2 to 3 feet (61 to 91 cm) tall spreading 12 to 24 inches (30 to 61 cm). Space each one so air can circulate freely between them, which holds mildew in check.
When to plant
Chocolate cosmos depends on warmth and will not survive frost. Where it is not hardy, sow fertile strains indoors in early spring, move plants outside after the cold breaks in late spring, and expect flowers from early summer through fall.
Northern hemisphere
Southern hemisphere
Typical months for a temperate climate: start earlier in warm zones, later where spring frosts linger.
- Sow: early spring (seed-grown strains only)
- Plant: late spring after last frost
- Harvest: early summer to fall
Hardiness
USDA hardiness zones: 7–9
Temperature: down to -18°C
Troubleshooting
Most problems with chocolate cosmos originate at the roots or in stagnant, crowded air. Spot the early symptoms and the remedies are straightforward. Find your symptom below, then act before it advances.
Soft tubers, rot below ground, and a plant that wilts or topples
What you are seeing is tuber and root rot, and the driver is soil that holds moisture far longer than the roots can tolerate, not a pathogen you treat with a spray. Dig up a failing plant and the tubers feel soft, look brown, and smell sour. Reduce watering, blend grit into the bed or shift to a raised bed, and throw out the rotted tubers, keeping only the firm ones to replant.
Fix:
- Stop overwatering and improve drainage
- Remove and discard severely rotted tubers
- Replant healthy tubers in gritty, well-drained soil or a raised bed
Tacky shoot tips colonized by small soft-bodied insects
The colonies massing on tender growth and buds are aphids, and you will frequently find ants working alongside them, farming the sticky honeydew. Blast them off with a firm spray of water, then mop up survivors with insecticidal soap. Dialing back nitrogen matters as well, because the soft, sappy growth that excess feeding produces is precisely what aphids prefer.
Fix:
- Dislodge aphids with a strong jet of water
- Treat persistent infestations with insecticidal soap
A chalky white film coating the foliage and stems
This is powdery mildew, a fungus that takes hold where plants crowd together in damp, stagnant air. The telltale sign is that the white bloom wipes clean off the leaf, distinguishing it from ordinary surface deposits. Thin the planting to let air move through, strip out the most heavily coated leaves, and direct water to the soil so foliage stays dry.
Fix:
- Improve spacing and airflow
- Remove badly affected foliage
Toxicity
Reassuring news for pet households: chocolate cosmos is safe. The ASPCA classes cosmos as non-toxic to cats, dogs, and horses, and the chocolate fragrance holds none of the theobromine that makes real chocolate dangerous. The worst likely outcome from a nibble is a mild, short-lived stomach upset, as with any non-food plant.
Safe for
People · Cats · Dogs · Horses · Rabbits · Livestock · Birds
Cats None
Safe in a household with cats. Because the ASPCA classes cosmos as non-toxic, an inquisitive nibble warrants no concern.
Dogs None
Poses no danger to dogs. Chewing a leaf or flower might bring on a brief, mild stomach upset, which is typical of most non-toxic plants.
Horses None
Safe for horses; the ASPCA confirms this across the entire cosmos genus. A horse that grazes a plant or two comes to no harm.
Rabbits Safe
Carries no toxicity for rabbits. As with any unfamiliar green, offer it in small portions at first so the digestive system can adapt.
Livestock Safe
Cattle, goats, and sheep can browse the plant without risk of poisoning. It holds no toxin worth worrying over.
Birds Safe
Safe for garden birds and poultry, which commonly peck at cosmos seed heads with no ill effect.
People Safe
Harmless to people. It is grown as a garden ornamental, not a food crop, so enjoy the dark flowers and their fragrance rather than putting it on the table.
Varieties
Only a handful of named forms of chocolate cosmos are in circulation, separated chiefly by flower color and how generously they flower. These are the selections you are most apt to encounter.
classic sterile clone
This is the long-cultivated original, bearing deep maroon-brown flowers that smell of chocolate; being sterile, it can only be increased by division or cuttings, never by seed.
'Choca Mocha'
A compact, heavy-blooming selection that produces more of the dark reddish-brown, chocolate-scented flowers than the old clone manages.
'Black Magic'
Chosen for its exceptionally dark maroon flowers that read as nearly black.
How to propagate
Since the classic plant is sterile, chocolate cosmos is usually increased by splitting tubers or rooting cuttings rather than by sowing seed.
DivisionModerate
Spring · One growing season
Divide the dormant tubers in spring, treating them much like a dahlia, and each division roots in over one growing season. Because the classic clone sets no viable seed, division is the method that holds it true to the parent.
Stem cuttingsModerate
Late spring to summer · Several weeks to root
Strike basal or stem cuttings from late spring through summer; over several weeks they root down into exact copies of the donor plant. For the seedless old clone, this is the standard route to increase stock.
SeedModerate
Early spring indoors · One season to flowering
Seed is an option only for the newer fertile strains, never the old sterile clone. Sow indoors in early spring and the seedlings come into flower during their first season.
Myths
Because chocolate cosmos has dark blooms and a chocolate smell, it must poison cats and dogs.
That aroma is purely a fragrance and contains none of the theobromine that makes genuine chocolate hazardous to animals. The ASPCA records cosmos as non-toxic to dogs, cats, and horses, and chocolate cosmos belongs to that very genus. Neither the dark petals nor the scent pose any threat.