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Tuberous summer-flowering perennial
Asteraceae
Fragrant tuberous perennial for sun, containers, and bouquets
Chocolate Cosmos
Cosmos atrosanguineus
Product code : VAN-COSMOS-ATROSANGUINEUS
Chocolate cosmos, now botanically classified as Cosmos atrosanguineus, produces deep red-brown, velvety daisy-like flower heads in late summer on slender stems approximately 50 to 70 cm (20 to 28 in) tall. Their cocoa fragrance intensifies toward evening and enriches borders, containers, and bouquets. This Van Noort package contains exactly one tuber. Plant them in sun, warm soil, and excellent drainage after the final frost. Because the plant is hardy only near Zone 9, tubers must be lifted before freezing weather, dried, and stored frost-free for replanting the following spring across colder Canadian regions. Its narrow footprint makes grouped planting easy, while evening scent rewards placement near outdoor living areas.
- Quantity
- 1 tuber
- Exposure
- Full sun
- Life cycle
- Tender perennial grown as an annual or overwintered in Quebec
- Hardiness
- Zone 9; overwinter frost-free in Quebec
Discover the plant
Common nameChocolate cosmos
FamilyAsteraceae
GenusCosmos
Speciesatrosanguineus
TypeTuberous summer-flowering perennial
Botanical nameCosmos atrosanguineus
Chocolate cosmos (Cosmos atrosanguineus) is a tuberous perennial prized for velvety deep red-brown flower heads and a delicate fragrance reminiscent of cocoa. Warmth intensifies the scent, especially near a patio or within a cutting garden. Finely divided dark green foliage forms a light 50 to 70 cm clump that lets dark flowers float above neighbouring plants. Renewed bloom from July until the first frosts brings depth, movement, and refinement to summer combinations. The Van Noort tuber starts this distinctive botanical species without sowing seed and develops into a graceful branching plant under sustained warmth.
Plant the tuber in spring after every frost risk has passed and soil has warmed. Set it 5 to 8 cm deep in fertile, light, freely drained soil under full sun, sheltered from strong wind. Allow 30 to 40 cm between plants. Water after planting, then maintain even moisture while letting the surface dry slightly between irrigations. Incorporate mature compost and feed moderately every three weeks during growth. Pinch young shoots to encourage branching and remove faded flowers regularly to stimulate more buds. Avoid saturated ground because dormant or cool tubers are vulnerable to rot before active roots develop.
Chocolate cosmos excels in a sunny border, a container at least 30 cm wide, or a bouquet garden. Pair this cocoa scented flower with salvias, gauras, verbenas, coneflowers, and grasses that highlight each deep red brown flower. Its heads attract bees, butterflies, and other useful insects over a long season. Before Quebec’s first frost, lift the chocolate cosmos tuber, let it dry briefly, and store it somewhere cool, dry, and frost-free. Inspect monthly and replant only firm tissue. Although its fragrance recalls chocolate, this ornamental plant is not intended for eating. Keep stored material clearly labelled through winter.
Sowing guide
It all startswith a seed.
Sowing depth
5 to 8 cm (2 to 3 in)
Spacing / density
30 to 40 cm (12 to 16 in)
Germination temperature
18 to 24°C (65 to 75°F)
Germination time
14 to 28 days
Sowing period
Plant in spring after all danger of frost
Propagation
Corms and separation of tuberlets during dormancy
Growing method
Wait until nights generally remain above 10°C and soil has warmed before planting, usually from late May into early June in Quebec. To advance bloom, start tubers indoors three or four weeks earlier in individual pots under bright light. Outdoors, choose full sun or light partial shade and loosen soil to 25 cm (10 in). Incorporate mature compost, plus coarse sand or fine gravel if drainage is slow. Set each tuber 5 to 8 cm (2 to 3 in) deep with the point upward, leaving 30 to 40 cm (12 to 16 in) between them. Cluster the single tuber rather than scattering them because the slender stems read more clearly together. Water after planting, then moderately until emergence. Once leaves appear, maintain consistent moisture and add light mulch that does not trap water against shoots. Feed at half strength during foliage development and again as buds form. Support groups discreetly in windy positions. Remove faded flowers without cutting leaves. After bloom, reduce watering gradually and allow foliage to yellow. Lift tubers before frost, dry them, remove soil, and store them somewhere cool, dry, and frost-free. Discard soft specimens before storage and label the sound tubers clearly. Inspect the stored group monthly so one damaged tuber cannot spread decay.
Soil and care
The right care,at the right time.
Soil pH
6.0 to 7.0
Minimum temperature
Not frost tolerant; lift tubers before temperatures reach 0°C
Care level
Moderate
Watering
After planting, water to settle the soil, then wait for shoots before increasing irrigation. During active growth and flowering, provide approximately 2.5 cm (1 in) of water weekly when rain is absent. Water at soil level in the morning and let the surface drain. Reduce moisture gradually after bloom so tubers mature before lifting. Consistent moisture supports even flowering stems. Containers may need more frequent checks during hot, windy weather.
Soil type
Light, fertile, freely draining soil enriched with mature compost is ideal. Sandy loam warms promptly and releases excess water after rain. Avoid compact clay, waterlogged hollows, and fresh manure. In containers, use quality potting mix amended with perlite and keep every drainage hole completely unobstructed throughout the growing season. Warm soil also advances the naturally late flowering season. Renew container mix yearly to prevent compaction and salt accumulation.
Fertilization
Incorporate mature compost before planting. When shoots reach 10 to 15 cm (4 to 6 in), apply balanced slow-release fertilizer or a half-strength liquid feed. Repeat once as buds begin forming. Avoid excess nitrogen, which promotes foliage and weak stems at the expense of flowers and the tuber’s stored energy. Stop feeding after bloom so foliage can mature naturally and tubers can enter dormancy with firm, well-ripened tissues.
Moisture
Maintain moderate, even moisture during active growth and flowering while allowing the soil surface to dry slightly between waterings. Chocolate cosmos performs poorly in cold saturated ground, especially before shoots emerge. Monitor containers more frequently during hot weather. Reduce water gradually in fall so the tuber can mature before dry storage, and always empty water-filled saucers promptly after rain or irrigation in Quebec gardens.
Seasonal care
In spring, sort stored tubers and discard any that are soft, mouldy, or completely shrivelled. Remove loose old tunics without injuring buds. Start them in pots near late April if earlier bloom is desired, or wait until outdoor soil becomes warm. Mark the planting area so late shoots are not disturbed. During summer, water deeply when the surface dries, weed by hand, and maintain a thin mulch. Apply balanced fertilizer at low strength during active growth, then stop once flowers open. Support stems in windy corridors and remove faded blooms above the foliage. For arrangements, harvest a flowering stem when its first bud opens while leaving every leaf intact. Watch for thrips, slugs, and spider mites; remove severely affected tissue and avoid wetting foliage in the evening. In fall, reduce water after the final flowers. Let leaves yellow naturally, then lift tubers before the first frost. Cut stems to 3 cm (1 in), dry everything for one to two weeks in a ventilated area, and separate tuberlets. Brush off soil, label Chocolate cosmos, and place tubers in paper bags or trays of dry peat. Through winter, keep them near 7 to 10°C, in darkness and protected from rodents. Inspect monthly and remove any rot immediately to protect the remaining lot. Do not store damp tubers or seal them in plastic. Record which groups flowered best so the strongest tubers can be replanted together next spring.
Container growing
A garden,within reach.
Recommended pot size
35 to 40 cm (14 to 16 in) wide and at least 30 cm (12 in) deep for 1 tuber
For one tuber, use a heavy container at least 35 to 40 cm (14 to 16 in) wide and 30 cm (12 in) deep. Select a pot with several holes and raise it slightly so water drains freely. Blend quality potting mix with mature compost and approximately one-quarter perlite or pumice. Arrange tubers 8 cm (3 in) deep and 7 to 10 cm (3 to 4 in) apart with points upward, then water once. Keep the container in sun and sheltered from prevailing wind. Before emergence, let the mix dry somewhat between applications; afterward, check several times weekly and water when the upper 2 to 3 cm (0.8 to 1.2 in) is dry. Feed at half strength every three weeks until flowers open. Insert a support ring before stems lengthen and rotate the pot regularly. Remove spent flowers but retain all leaves. Once foliage yellows, stop watering. Move the entire pot into a dry, dark, frost-free space, or lift, dry, and store tubers separately. The following spring, replace at least one-third of the mix, sort tuberlets, and replant only firm tubers. Separate vigorous tuberlets for growing on in smaller nursery pots. Never overwinter the container outdoors where repeated freezing and thawing can destroy the tubers.
Bloom and dimensions
Its place,in your garden.
Mature height
50 to 70 cm (20 to 28 in)
Width / spread
30 to 40 cm (12 to 16 in)
Flower color
Deep red-brown to dark burgundy
Foliage color
Dark green
Foliage type
Deciduous, strap-like, and sword-shaped
Growth rate
Moderate
Growth habit
Light, upright, branching clump
Fragrance
Delicate cocoa fragrance, strongest in warm weather
Bloom period
From late August through September, deep red-brown, star-shaped flowers open successively along slender flowering stems. Every bloom carries a dark central disc and releases cocoa fragrance, especially toward evening. An indoor start and warm site advance flowering. Cut flowering stems when the first bud opens for arrangements, and leave the foliage intact so tubers rebuild reserves. Remove rain-damaged blooms to protect later buds.
Garden associations
In goodcompany.
Companion plants
Choose dahlias, compact cannas, salvias, verbenas, cosmos, zinnias, and fine grasses that share a preference for sun, warmth, and draining soil. Purple or bronze foliage echoes the dark flower throat, while blue blooms provide a cool contrast. Avoid bog plants and dense groundcovers that trap moisture around tubers or complicate fall lifting and sorting. Compact Joe-Pye weed and late black-eyed Susans extend the September display around the flowering stems. Leave open soil around each cluster so lifting tools can enter without damaging neighbouring crowns, and maintain clear airflow during humid weather.
Frequently asked questions
Your questions,answered.
How deep and in which direction should the tubers be planted?
Set each tuber 5 to 8 cm (2 to 3 in) deep, with the small point or bud facing upward and the flatter base downward. Leave approximately 30 to 40 cm (12 to 16 in) between units and cluster the single tuber for a visible effect. If orientation is difficult to recognize, place the tuber on its side; the shoot will turn upward naturally. Wait until soil is warm and frost danger has passed. In heavy ground, add fine gravel or plant on a slight mound. Water after planting, then only moderately until leaves appear to reduce the risk of rot. Mark the group clearly after planting because emergence may be later than nearby annuals.
Why does my chocolate cosmos fail to bloom before frost?
This species flowers naturally late and may lack sufficient heat during a short summer. Start tubers indoors three or four weeks before planting, using small pots under bright light. Transplant without disturbing roots once nights stay above 10°C. Choose the warmest, sunniest garden position, ideally beside a wall or stone edge. Excess nitrogen produces abundant leaves but delays buds, so feed moderately. Keep soil moist during active growth without saturating it. Small tubers or tuberlets may also require more than one season before producing a complete flowering flowering stem. Preserve their foliage and store them carefully so they can gain size.
How should tubers be stored through a Canadian winter?
After flowering, reduce watering and let foliage yellow so stored energy returns to the tuber. Lift before the first frost, cut stems to approximately 3 cm (1 in), and gently shake off soil. Dry tubers for one to two weeks in a ventilated location away from direct sun. Remove very loose tunics and separate tuberlets without injuring the base. Store tubers in a paper bag or ventilated box with dry peat, near 7 to 10°C. Label the plant, protect it from rodents, and inspect monthly so any soft or mouldy piece is removed immediately. Keep the material dry but not exposed to heated household air.
How can strong stems be produced for bouquets?
Provide at least six hours of sun, fertile soil without excess nitrogen, and consistent moisture while stems elongate. In a windy site, install a support ring early, before flowering stems bend. Harvest when the first bud shows colour or begins opening. Work in the morning with a clean tool and leave several leaves on the plant so the tuber retains vigour. Recut the base under water, remove only leaves that would be submerged, and place the stem in a clean vase. Change water every two days; upper buds generally continue opening and releasing fragrance. Keep the arrangement away from direct heat and ripening fruit.
Is chocolate cosmos safe around pets?
No. Cosmos atrosanguineus belongs to the same genus as garden gladiolus and should be considered toxic to dogs, cats, and some other animals if swallowed. Corms present the greatest concern, but leaves and flowers are not intended for consumption. Keep packages, stored tubers, and planting debris in closed containers beyond reach. Collect dropped pieces during cleanup and avoid a site where pets routinely dig. If ingestion is suspected and drooling, vomiting, diarrhea, weakness, or abdominal pain develops, contact a veterinarian promptly and provide the name Cosmos atrosanguineus. Do not induce vomiting without professional instructions. Wear gloves if handling the sap irritates your skin.
Wildlife and pets
Life,around your plants.
Reported toxicity
Yes
Supporting wildlife
Star-shaped flowers may attract daytime butterflies and some long-tongued pollinators, while evening fragrance signals blooms to insects active near dusk. This contribution is complementary within a diverse garden. Avoid insecticides, retain several uncut flowering stems, and grow nearby nectar plants with more accessible flowers to support a broader range of visitors.