Ornamental · Asteraceae
Chocolate Cosmos
Cosmos atrosanguineus
Deep maroon flowers that genuinely smell of dark chocolate, growing 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 in two ways at once, with flowers as dark as good chocolate and a scent to match on a warm afternoon. A native of Mexico and a member of the daisy family, it grows from a small tuber instead of a fibrous root. Almost every plant you can buy descends from one sterile clone that gardeners have shared by division for many generations, which means you are growing a little piece of history.
This is a small, friendly plant, topping out around 2 to 3 feet (61 to 91 cm) tall, holding its flowers on slender stems above soft, ferny leaves. The blooms keep coming from early summer right through fall, so you get a long stretch of color whether it lives in a border or a pot. Snip a few stems for a vase and that chocolate scent drifts indoors with them.
Think of it as a tender perennial. It only returns year after year in mild areas, so where winters get cold most gardeners simply lift the tubers and store them dry the way they handle dahlias, then replant once spring arrives. There is plenty of room for a first try to go well.
Care
The short version: full sun, average soil that drains freely, and a light hand with the watering can. Let the top half of the soil dry out between drinks, feed sparingly, and keep the tubers out of soggy ground.
Light
Give chocolate cosmos full sun, a place that catches direct light for most of the day. Plenty of sun draws out the richest flower color and keeps those slim stems sturdy instead of stretched and floppy.
Water
Water with a light touch and let the top half of the soil dry before watering again. The plant handles dry to average soil happily, but wet ground rots the tubers quickly, so when in doubt lean dry and never leave it sitting in water.
Soil
Set it in average, well-drained soil with moderate fertility. Good drainage matters far more than richness, because the tubers can't survive in heavy, waterlogged ground. If your soil holds water, simply mix in grit or use a raised bed and you are all set.
Humidity
Everyday outdoor humidity suits it perfectly, so there's no number to fuss over. Air movement counts for more, since crowded, stagnant conditions are what tempt powdery mildew onto the leaves.
Feeding
A light feed across the growing season is truly all it needs. Overdo it and you'll end up with lots of leaves and fewer flowers, so keep it gentle and let the plant pour its energy into blooming.
Pruning
Deadhead the faded flowers as they go over and the plant will keep setting new buds for longer. Trim away any damaged or diseased growth whenever you notice it, and the plant stays tidy and healthy.
Size & spacing
Plan for a plant 2 to 3 feet (61 to 91 cm) tall with a spread of 12 to 24 inches (30 to 61 cm). Leave enough space between them for air to flow freely, which is your easiest way to keep mildew away.
When to plant
Chocolate cosmos loves warmth and will not stand up to frost, so timing is your friend here. Where it isn't hardy, sow fertile strains indoors in early spring, move plants outside once the cold has truly passed in late spring, and then enjoy the flowers all the way from early summer into 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 hiccups with chocolate cosmos begin either underground or in still, crowded air, and the good news is that early signs are easy to read. Spot them soon and the fixes are gentle and simple. Match what you see to the notes below, then step in before anything spreads.
Soft tubers and a plant that droops or falls over
Take heart, because this is tuber and root rot, and it comes from soil staying soggy too long rather than a disease you have to chase down with sprays. When you gently lift a sad-looking plant, the tubers will feel soft and brown and smell off. Ease back on watering, mix some grit into the bed or move things to a raised bed, and toss only the rotted tubers while keeping the firm ones to replant. The recovery really is in your hands.
Fix:
- Stop overwatering and improve drainage
- Remove and discard severely rotted tubers
- Replant healthy tubers in gritty, well-drained soil or a raised bed
Sticky shoot tips covered in tiny soft insects
Those little clusters gathering on fresh growth and buds are aphids, and you may notice ants hanging around for the sweet honeydew the aphids leave. Don't worry, they are easy to send packing: a firm spray of water knocks most of them away, and insecticidal soap tidies up any that hold on. Going lighter on nitrogen feeding helps as well, since soft, leafy new growth is what tempts them in the first place.
Fix:
- Dislodge aphids with a strong jet of water
- Treat persistent infestations with insecticidal soap
A white dusty film spreading over leaves and stems
What you are seeing is powdery mildew, a fungus that moves in when plants are packed together in damp, motionless air. You can tell it apart from harmless residue because the white patches wipe away from the leaf. Give the planting more breathing room, snip off the most affected leaves, and water down at the base so the foliage stays dry. It is very manageable once you make those small changes.
Fix:
- Improve spacing and airflow
- Remove badly affected foliage
Toxicity
Here is some welcome news for pet owners: chocolate cosmos is safe. The ASPCA lists cosmos as non-toxic to cats, dogs, and horses, and that chocolate scent carries none of the theobromine that makes real chocolate harmful. The worst you might see is a mild, short-lived stomach upset, no different from any other non-food plant.
Safe for
People · Cats · Dogs · Horses · Rabbits · Livestock · Birds
Cats None
Perfectly fine around cats. Cosmos is on the ASPCA non-toxic list, so a curious taste here and there is nothing to worry about.
Dogs None
No danger to dogs. If one chews a leaf or flower it might have a brief, mild tummy upset, much like with any non-toxic plant.
Horses None
Safe for horses, something the ASPCA confirms across the whole cosmos genus. A nibble on a plant or two does no harm at all.
Rabbits Safe
Not toxic to rabbits. As you would with any fresh green, offer just a little at first so their digestion can adjust.
Livestock Safe
Cattle, goats, and sheep can graze on it safely. The plant holds no toxin that could cause poisoning.
Birds Safe
Fine for garden birds and poultry, which often peck happily at cosmos seed heads with no problems.
People Safe
Harmless to people. Keep in mind it is a garden ornamental and not a food crop, so enjoy it for the dark blooms and the scent rather than for eating.
Varieties
Just a handful of named chocolate cosmos forms are out there, and they vary mostly in their flower color and how generously they bloom. Here are the ones you are most likely to come across.
classic sterile clone
This is the long-cherished original, with deep maroon-brown flowers that smell of chocolate. Being sterile, it only multiplies through division or cuttings, never seed.
'Choca Mocha'
A tidy, generous bloomer that produces more of those dark reddish-brown, chocolate-scented flowers than the older clone does.
'Black Magic'
Loved for flowers in the deepest, nearly black shade of maroon.
How to propagate
Since the classic plant is sterile, you'll find most chocolate cosmos is increased by splitting tubers or rooting cuttings rather than by sowing seed, and both are approachable.
DivisionModerate
Spring · One growing season
When the tubers are dormant in spring, divide them just like you would a dahlia, and each piece needs only a single growing season to find its feet. With the classic clone being sterile, this is how you keep it true to the parent, so don't be shy about trying it.
Stem cuttingsModerate
Late spring to summer · Several weeks to root
From late spring through summer you can take basal or stem cuttings, which take several weeks to root into faithful copies of the parent. It is the usual way to bulk up the old clone, since it never sets seed of its own.
SeedModerate
Early spring indoors · One season to flowering
Seed is only an option for the newer fertile strains, not the old sterile clone, so check what you have first. Sow it indoors in early spring and the plants will flower within that same season.
Myths
Because chocolate cosmos is so dark and smells of chocolate, it must be poisonous to cats and dogs.
You can relax on this one. The smell is purely an aroma and holds none of the theobromine that makes real chocolate harmful to pets. Cosmos is listed by the ASPCA as non-toxic to dogs, cats, and horses, and chocolate cosmos belongs to that very same genus. The dark blooms and the scent are nothing to fear.