Hibiscus trionum

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black-eyed Susan

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black-eyed Susan RHS
black-eyed Susan RHS / Joanna Kossak

Other common names

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, African ketmia

Synonyms

Hibiscus africanus

Annual Biennial
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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

Position

Full sun

Soil Types

Loam, Sand

Max Height

0.5-1 metres

Max Spread

0.1-0.5 metres

Size

Time to Maturity
1–2 years
Max Spread
0.1-0.5 metres
Max Height
0.5-1 metres

Growing Conditions

Loam Sand
Moisture
Well–drained
pH
Acid or Neutral

Position

Full sun
Aspect
South–facing or West–facing
Exposure
Sheltered
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 & Scent

Season Stem Flower Foliage Fruit
Spring
Summer
Autumn
Winter

Botanical Details

Family
Malvaceae
Native to GB/Ireland
No
Foliage
Deciduous
Habit
Columnar upright
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
Name Status
Correct
Plant Range
Africa, SW Asia

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

  • Cottage and informal garden
  • Sub-tropical
  • City and courtyard gardens
  • Patio and container plants
  • Flower borders and beds

Pruning

No pruning required

Pests

May be susceptible to aphids, scale insects, mealybugs and glasshouse whitefly when grown under glass

Diseases

May be susceptible to honey fungus (rarely) and powdery mildews