• 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 bipinnatus

cosmea

cosmea

© RHS

  • Other common names cosmea
    Mexican aster

    purple Mexican aster
    Spanish needles

    see more
  • 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. bipinnatus is a tall, bushy annual to 2.5m, with very finely divided, mid-green leaves, and large flowers to 8cm across, usually white or pink the wide outer rays surround a central disc of tightly clustered, usually yellow, inner disc florets. Flowering late summer and into autumn, until frost occurs. Many named cultivars and selections are available, including doubles, forms with tubular rays, and picotee colours

  • Plant range Mexico, S US

Characteristics

  • Foliage Deciduous

  • 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 Exposed or Sheltered

Soil

  • Loam

    Loam

  • Sand

    Sand

  • Chalk

    Chalk

  • MoistureMoist but well-drained

  • SoilLoam, Sand, Chalk

  • pHAcid, Alkaline, Neutral

Size

  • Ultimate height 1.5-2.5 metres

  • Ultimate spread 0.1-0.5 metres

  • Time to ultimate height 1-2 years

How to grow

Cultivation Grow in moderately fertile, moist, but well-drained soil in full sun. Deadhead flowers to prologue flowering season. Leave a few seedheads to ripen to selfseed if required

Propagation Propagate by seed at 16°C in mid-spring under glass, or in situ in late spring

Suggested planting locations and garden types City & Courtyard Gardens Cottage & Informal Garden Patio & Container Plants Prairie Planting Wildlife Gardens Wildflower meadow

How to care

Pruning none required

Pests Aphids and slugs may be troublesome

Diseases Susceptible to grey moulds

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