• AGM plants

    AGM plants have been through a rigorous trial and assessment programme. They are:

    • Excellent for ordinary use in appropriate conditions
    • Available to buy
    • Of good constitution
    • Essentially stable in form & colour
    • Reasonably resistant to pests & diseases

Cosmos sulphureus

yellow cosmos

yellow cosmos

© RHS

  • Other common names yellow cosmos

  • Synonyms Bidens sulphurea

  • Family Asteraceae

  • Genus Cosmos can be annuals or perennials with simple or pinnately divided leaves and large, long-stalked daisy-like flowers in summer

  • Details C. sulphureus is a half-hardy annual with fresh, fern-like foliage and a long flowering season. Selections are variable in height, most between 50cm and 1m, but including some dwarf forms. Flower colour is varied, in many tones of yellow, orange and red

  • Plant range Mexico, C America, N S America

Characteristics

  • Habit Columnar/Upright

  • Hardiness

    Hardiness ratings

    All ratings refer to the UK growing conditions unless otherwise stated. Minimum temperature ranges (in degrees C) are shown in brackets

    • H1a - Under glass all year (>15C)
    • H1b - Can be grown outside in the summer (10 - 15)
    • H1c - Can be grown outside in the summer (5 - 10)
    • H2 - Tolerant of low temperatures, but not surviving being frozen (1 to 5)
    • H3 - Hardy in coastal and relatively mild parts of the UK (-5 to 1)
    • H4 - Hardy through most of the UK (-10 to -5)
    • H5 - Hardy in most places throughout the UK even in severe winters (-15 to -10)
    • H6 - Hardy in all of UK and northern Europe (-20 to -15)
    • H7 - Hardy in the severest European continental climates (< -20)

    H3

Colour

Sunlight

  • Full Sun

  • Aspect South-facing or West-facing

  • Exposure Sheltered

Soil

  • Sand

    Sand

  • Chalk

    Chalk

  • Loam

    Loam

  • MoistureMoist but well-drained

  • SoilSand, Chalk, Loam

  • pHAcid, Alkaline, Neutral

Size

  • Ultimate height 0.1-0.5 metres

  • Ultimate spread 0.1-0.5 metres

  • Time to ultimate height 1 year

How to grow

Cultivation Grow in moderately fertile, moist but well-drained soil in full sun

Propagation Propagate by seed in mid spring

Suggested planting locations and garden types Cut Flowers Flower borders and beds City & Courtyard Gardens Cottage & Informal Garden Sub-tropical

How to care

Pruning Deadheading should be carried out regularly to prolong flowering

Pests Aphids and slugs may be a nuisance

Diseases grey mould may be a problem

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