Plant chocolate cosmos from a tuber after frost, in full sun and draining ground. Cosmos atrosanguineus is the botanical name. It is not a pink seed mix with the word chocolate on the packet.
Full sun, draining soil, and water when the top is dry
| Factor | Recommended | Avoid |
|---|---|---|
| Light | All-day sun, at least six hours | A shady wall that stretches stems and kills scent |
| Soil | Average ground that drains | Wet clay that sits on the tuber |
| Water | When the top inch or two is dry | A weekly puddle |
| Feed | Skip, or one light spring dose | Heavy nitrogen that makes leaves, not flowers |
Give chocolate cosmos heat and drain first. [1] Skip rich feed; extra nitrogen makes a leafy plant with a thin bloom. [2] Once the plant is up, water when the top of the soil is dry. Pinch the tip once when the plant is about 8 to 12 inches tall, then deadhead spent flowers if you want more bloom.
Is chocolate cosmos a perennial?
Yes, as a tender tuber. Where winters freeze, lift and store the clump. Mild-winter beds on sharp drain can leave it in.
Why isn’t my chocolate cosmos blooming?
Usually too little sun or too much fertilizer. Move it into full sun and stop the feed.
How to plant a chocolate cosmos tuber
Buy a tuber or a started plant. Wait until frost has passed and the soil has warmed. The clump may sit quiet for several weeks after you plant it — that is normal.
- Loosen draining soil in full sun. Do not dump a fertilizer bag into the hole.
- Set the tuber on its side about 2 inches deep, with at least one eye facing up. Space clumps 12 to 18 inches apart. [3]
- Cover, water in, then keep the soil barely moist — not wet — until shoots show.
- A 12-inch draining pot holds one tuber if you want the clump close to a seat, or if you plan to move the pot for winter.
When do you plant chocolate cosmos?
After the last spring frost, as a dormant tuber or a started plant. Do not sow a pink mix for this species.
How to lift and store the tubers
Treat the clump like a dahlia. Where frost is rare and the ground drains, you can cut yellowed tops and leave it in. Where winters freeze, or where winter stays wet, lift.
- After frost blacks the tops, cut stems to a few inches. Dig a wide circle with a fork so you do not slice the tuber. [4]
- Brush off soil. Discard anything soft or foul. Let the clump dry for a few days in a cool, airy place out of sun.
- Store in a ventilated crate or box, packed so pieces do not touch, in a dark, frost-free spot that stays cool and dry.
- In a pot: cut tops to a few inches and move the dry pot to the same kind of spot. Do not water until green shows in spring.
- Check monthly. Throw out rot. If a firm tuber shrivels, mist the packing lightly. Do not trash a firm clump in spring because it is slow to wake.
How do you overwinter chocolate cosmos?
Lift after frost, dry the clump, and store it cool and dry like a dahlia. Or move the whole pot frost-free and keep it dry until shoots return.
Can I leave chocolate cosmos in the ground?
Only where winters stay mild and the soil drains. Wet, freezing ground rots the tuber. Lifting is the safer habit.
- Rot in the crate — the clump went in wet, or pieces touched. Dry longer next time; pack so they sit apart.
- No shoots in April — chocolate cosmos is slow to break dormancy. Wait for warmth before you throw the tuber out.
- Leaves, no flowers — too much feed or too little sun. Same rule as the Factor table.
Plant the tuber after frost in draining sun. Water when the top is dry. Lift and store where winters freeze.
FAQ
Can chocolate cosmos live in a pot?
Yes. Use a draining pot about 12 inches wide, one tuber, full sun. The pot is also the easy winter move.
Should I pinch chocolate cosmos?
Once, when the plant is about 8 to 12 inches tall. Then deadhead spent flowers if you want more bloom.
How tall do chocolate cosmos get?
Usually about 2 to 3 feet, shorter than tall garden cosmos. Compact shop plants can stay near a foot.
Can I grow chocolate cosmos from seed?
The classic clone is often sterile. Buy a tuber or a plant. Some newer strains set a little seed — that is not the same as a pink mix packet.
Are chocolate cosmos edible?
No. The chocolate scent is vanillin in the petals. Do not eat the flowers.
Do chocolate cosmos attract butterflies?
Yes. Open flowers on a warm day are the useful landing pads. Plant them where you will walk past the scent.
When do chocolate cosmos bloom?
Midsummer into the first hard frost, strongest on warm afternoons.
Can I divide chocolate cosmos in fall?
You can tease a crowded clump when you lift. Each piece needs an eye and a bit of stem. Spring divide is kinder if the tuber bruises easily.
Do I fertilize chocolate cosmos every week?
No. Skip it, or use one light spring dose. Weekly feed makes leaves.
Related guides
Recommended plants
References
- [1] Gardener's Path -
https://gardenerspath.com/plants/flowers/grow-chocolate-cosmos/ - [2] Utah State University Extension -
https://extension.usu.edu/yardandgarden/research/cosmos-in-the-garden - [3] Longfield Gardens -
https://www.longfield-gardens.com/blogs/perennial-plants-all-about/all-about-chocolate-cosmos - [4] Wisconsin Horticulture -
https://hort.extension.wisc.edu/articles/storing-tender-bulbs-for-winter/
This note is part of Cosmos Guides.
More first-season notes by plant are gathered in How to Grow Guides.
Updated: Reviewed by Bosquelle Editors