Ornamental · Asteraceae
Chocolate Cosmos
Cosmos atrosanguineus
Deep maroon blooms that genuinely smell of dark chocolate, rising from a tender tuber you tend much like 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, with flowers in the shade of dark chocolate and, on a warm afternoon, a scent to go with it. Native to Mexico and part of the daisy family, it rises from a small tuber instead of fibrous roots. Nearly every plant on sale leads back to one sterile clone, handed down by division across many gardeners and many seasons.
Its scale stays restrained, topping out at 2 to 3 feet (61 to 91 cm) and holding its flowers on slender stems above feathery foliage. Blooms keep coming from early summer deep into fall, so it stays a steady note of color whether you set it in a border or a container by the door. Snip a few stems for the table and that chocolate scent drifts through the room.
Treat it as a tender perennial. Only in mild zones will it return on its own, so where the cold bites most people lift the tubers and keep them dry through winter, exactly as they would a dahlia, then settle them back into the ground come spring.
Care
The short version: full sun, ordinary free-draining soil, and a restrained hand with water. Let the top half of the soil dry before the next drink, feed lightly, and keep those tubers out of wet ground.
Light
Place chocolate cosmos in full sun, somewhere it catches direct light through most of the day. That strong light is what draws out the richest flower color and keeps the slim stems upright instead of reaching and toppling.
Water
Keep watering light and wait for the top half of the soil to dry before the next round. The plant copes happily with dry to average soil, yet wet ground rots the tubers in short order, so lean toward dry and never leave it standing damp.
Soil
Set it in average, well-drained soil of middling fertility. Sharp drainage matters far more than richness here, because the tubers cannot pull through in heavy, sodden ground. If your soil holds water, mix in grit or give it a raised bed.
Humidity
Everyday outdoor humidity suits it perfectly, so there's no figure to aim for. Moving air is the thing that counts, since crowded, still surroundings are what coax powdery mildew onto the leaves.
Feeding
A light feed across the growing season covers everything it needs. Overdo it and you'll see leaves at the cost of flowers, so keep a gentle hand and let the plant pour its energy into blooming.
Pruning
Deadhead the faded flowers as they go over and the plant keeps setting fresh buds for longer. Trim away any damaged or diseased growth the moment you notice it to keep things looking sharp.
Size & spacing
Plan for a plant 2 to 3 feet (61 to 91 cm) tall spreading 12 to 24 inches (30 to 61 cm) wide. Leave enough space between plants for air to flow freely around each one, which holds mildew off.
When to plant
Chocolate cosmos asks for warmth and will not stand frost. Where it isn't hardy, sow fertile strains indoors in early spring, move plants outside once the chill has lifted in late spring, and look forward to 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
Trouble here tends to begin out of sight, down at the tubers or in stagnant, crowded air. Spot the first signs and the remedies are straightforward. Find the description that fits what you're seeing, then step in before it spreads.
A border plant that slumps while its tubers turn to mush
What looks like a sudden decline is tuber and root rot, and the culprit is a bed that holds moisture for too long, not anything a spray can correct. Ease a faltering plant out of the ground and the tubers feel soft and smell off. Pull back on watering, fold grit into the soil or shift the planting to a raised bed, and toss the spoiled tubers so only the firm ones go back in.
Fix:
- Stop overwatering and improve drainage
- Remove and discard severely rotted tubers
- Replant healthy tubers in gritty, well-drained soil or a raised bed
Tender new tips gone tacky and dotted with tiny insects
The small bodies massing on fresh shoots and buds are aphids, frequently with ants nearby, drawn to the sticky honeydew the colony leaves on the foliage. A firm spray of water sends most of them flying, and insecticidal soap handles the holdouts. Going lighter on nitrogen pays off as well, since the soft, succulent growth it produces is precisely the kind aphids gather on.
Fix:
- Dislodge aphids with a strong jet of water
- Treat persistent infestations with insecticidal soap
A chalky white bloom creeping over leaves and stems
This pale dusting is powdery mildew, a fungus that takes hold where plants crowd together in damp, motionless air. Unlike harmless residue, these patches wipe away under a finger, which tells you what you're looking at. Thin the planting so air can pass through, strip out the most affected leaves, and direct your watering to the base to keep the foliage dry.
Fix:
- Improve spacing and airflow
- Remove badly affected foliage
Toxicity
Reassuring news if you share the house with animals: chocolate cosmos is safe. The ASPCA records cosmos as non-toxic to cats, dogs, and horses, and that chocolate scent holds none of the theobromine that makes real chocolate a danger. A taste might bring on a brief, mild stomach upset at worst, no different from any other non-food plant.
Safe for
People · Cats · Dogs · Horses · Rabbits · Livestock · Birds
Cats None
Easy company for cats. With the ASPCA listing cosmos as non-toxic, an inquisitive nibble calls for no concern.
Dogs None
Nothing for dog owners to worry over. A dog that mouths a leaf or bloom might have a brief, mild stomach upset, as happens with most non-toxic plants.
Horses None
Fine around horses, a point the ASPCA confirms for cosmos as a whole. A mouthful or two does no damage.
Rabbits Safe
Holds no toxicity for rabbits. As you would with any fresh green, offer just a little at first so the gut can settle into it.
Livestock Safe
Cattle, goats, and sheep can graze it with no risk of poisoning. The plant simply carries no toxin to cause trouble.
Birds Safe
Fine for garden birds and poultry, which regularly pick at cosmos seed heads without any ill effect.
People Safe
No hazard to people. Think of it as a decorative plant rather than something for the kitchen, grown for its dark flowers and scent and not for eating.
Varieties
Only a handful of named chocolate cosmos make the rounds, set apart mainly by flower color and how readily they bloom. These are the ones most likely to turn up where you shop.
classic sterile clone
The form gardeners have grown for ages bears deep maroon-brown, chocolate-scented flowers and produces no seed, so it travels only through division or cuttings.
'Choca Mocha'
A tidy, generous bloomer that puts out more of the dark reddish-brown, chocolate-scented flowers than the long-standing clone.
'Black Magic'
A selection valued for blooms in the deepest maroon, near enough to black to read that way in the border.
How to propagate
Since the classic plant sets no seed, most chocolate cosmos is increased by splitting tubers or rooting cuttings rather than by sowing.
DivisionModerate
Spring · One growing season
Divide the dormant tubers in spring, in much the same way you handle a dahlia, and each section finds its feet across one growing season. With the classic clone setting no seed, division is what holds it true to the parent.
Stem cuttingsModerate
Late spring to summer · Several weeks to root
Pull basal or stem cuttings from late spring through summer, and over several weeks they root into faithful copies of the parent. This is the go-to method for building up stock of the old clone, which never seeds on its own.
SeedModerate
Early spring indoors · One season to flowering
Seed is an option only with the newer fertile strains, never the old sterile clone. Sow it indoors in early spring and the seedlings come into flower during their opening season.
Myths
The dark color and chocolate scent of chocolate cosmos mean it is poisonous to cats and dogs.
That fragrance is purely aromatic and holds none of the theobromine that makes true chocolate a hazard to pets. The ASPCA records cosmos as non-toxic to dogs, cats, and horses, and chocolate cosmos belongs to the very same genus. Neither the moody blooms nor the scent give you anything to fret about.