• 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

Hibiscus trionum

black-eyed Susan

black-eyed Susan

© RHS

  • Other common names black-eyed Susan
    bladder hibiscus

    bladder ketmia
    devil's head in a bush
    flower of an hour
    flower of the hour
    goodnight at noon
    modesty
    trailing hollyhock
    Venice mallow
    Venus's mallow

    see more
  • Synonyms Hibiscus africanus

  • Family Malvaceae

  • Genus Hibiscus can be deciduous or evergreen shrubs, trees, annuals or perennials, with simple or palmately lobed leaves and large, funnel-shaped flowers over a long flowering season

  • Details H. trionum is an upright annual, to 60cm tall, with oval, serrated leaves. The creamy-white or pale yellow flowers, with purplish-brown centres, are borne from late summer to early autumn and followed by bladder-like seed capsules

  • Plant range Africa, SW Asia

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)

    H2

Colour

Sunlight

  • Full Sun

  • Aspect South-facing or West-facing

  • Exposure Sheltered

Soil

  • Loam

    Loam

  • Sand

    Sand

  • MoistureWell-drained

  • SoilLoam, Sand

  • pHNeutral, Alkaline

Size

  • Ultimate height 0.5-1 metres

  • Ultimate spread 0.1-0.5 metres

  • Time to ultimate height 1-2 years

How to grow

Cultivation Plant outside when threat of frosts has passed and grow in a well-drained soil in full sun

Propagation Propagate by seed

Suggested planting locations and garden types Flower borders and beds City & Courtyard Gardens Cottage & Informal Garden Patio & Container Plants Sub-tropical

How to care

Pruning None required

Pests May be affected by aphids and thrips

Diseases Powdery mildews may be a problem

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