PLNTversePLNTverse
Plants › Seasonal bedding

sulphur cosmos (Cosmos sulphureus)

Cosmos sulphureus is an upright or much-branched herb commonly grown horticulturally as a seasonal flowering plant. Sources differ in describing its life cycle: it is described as an annual, sometimes as a half-hardy annual, and it may reappear through self-sowing in subsequent years.

LightFull sun is considered best, although sources differ on tolerance of partial shade; insufficient light may cause abnormal leaf form and poor flowering.
WaterKeep conditions moderately moist during establishment; established plants tolerate drought and suit relatively dry to moderately moist, well-drained soil, while standing water and prolonged excessive moisture should be a
TemperatureA USDA hardiness-zone classification is reported for Cosmos sulphureus. It is generally frost tender; keep above freezing.
Track your sulphur cosmos in the PLNTverse app
sulphur cosmos illustration

Overview

Cosmos sulphureus is an upright or much-branched herb commonly grown horticulturally as a seasonal flowering plant. Sources differ in describing its life cycle: it is described as an annual, sometimes as a half-hardy annual, and it may reappear through self-sowing in subsequent years.

Origin and habitat

Sources differ on its native range: it is primarily regarded as native to Mexico and Central America, while some accounts extend the range into northern or broader South America. Native records occur at lower elevations in Mexico, while escaped populations have been recorded along roadsides, in moist grassland, on shrubby slopes, and across a range of elevations. It is suited to sunny, warmer conditions, tolerates heat, and established plants have some drought tolerance; frost limits flowering and growth.

Characteristics

Sources differ on mature height, giving a range of about 30–210 cm, while the few available records report a mature spread of about 10–50 cm. It grows quickly, reproduces readily, and mature seed readily self-sows. The leaves are reported to be opposite and deeply pinnately divided, also described as bipinnately compound with lance-shaped segments; compared with Cosmos bipinnatus, they are broader with coarser segments. The flower heads are mainly yellow, golden yellow, or orange, with red also occurring in cultivated forms, and include single, semi-double, and double types; flowering is prolonged, although sources differ on its seasonal timing.

Light

Full sun is considered best, although sources differ on tolerance of partial shade; insufficient light may cause abnormal leaf form and poor flowering.

Watering

Keep conditions moderately moist during establishment; established plants tolerate drought and suit relatively dry to moderately moist, well-drained soil, while standing water and prolonged excessive moisture should be avoided.

Temperature and dormancy

A USDA hardiness-zone classification is reported for Cosmos sulphureus. It is generally frost tender; keep above freezing.

Growing medium and mounting

Cosmos sulphureus adapts to a wide range of soils, including poor, dry, or sandy soil, with good drainage preferred; records also indicate tolerance of acidic, neutral, and alkaline soils.

Feeding

It has low soil-fertility requirements, and overly fertile soil may produce taller plants that are more prone to lodging.

Propagation

Propagation is mainly by seed and self-sowing is easy, while some sources also report propagation by shoot cuttings; sources differ on reported germination timing and conditions.

Common problems

Serious pest problems are generally reported to be uncommon, although aphids may occur around young shoots from early summer into summer, and slugs are also reported to feed on the leaves. Diseases are generally uncommon, although a southern blight problem of herbaceous ornamentals is also listed for the plant. Excess water or poor drainage may cause seed rot and lodging, insufficient light may lead to abnormal leaf form and reduced flowering, and fertile soil may produce overly tall plants prone to lodging. It is sensitive to frost or freezing; tall cultivars may need support in strong winds and frequent heavy rain, while waterlogging from heavy rain during early sowing may cause seed rot.

Identification

Cosmos sulphureus is much-branched, with deeply pinnately divided leaves and characteristically bright yellow to orange flowers; compared with Cosmos bipinnatus, its leaves are broader and it is usually more tolerant of summer heat.

Photos

Cosmos sulphureus
📷 Alejandro Bayer Tamayo from Armenia, Colombia · CC BY-SA 2.0 · source
Cosmos sulphureus
📷 Aris riyanto · CC BY 3.0 · source
Cosmos sulphureus
📷 Krzysztof Golik · CC BY-SA 4.0 · source

Sources