• 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

Advertise here

Did you find the information you were looking for?

RHS members can get exclusive individual advice from the RHS Gardening Advice team.

Join the RHS now

Get involved

We're a UK charity established to share the best in gardening. We want to enrich everyone's life through plants, and make the UK a greener and more beautiful place.