• 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

Rhododendron williamsianum

Williams rhododendron

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
Williams rhododendron

© RHS

  • Other common names Williams rhododendron

  • Family Ericaceae

  • Genus Rhododendron can be evergreen or deciduous shrubs or trees, with simple leaves, sometimes with a dense colourful indumentum of hairs on the lower side, and funnel-shaped, bell-shaped or tubular flowers that may be solitary or in short racemes

  • Details R. williamsianum is a compact, spreading small shrub with neat rounded or heart-shaped leaves, bronze when young and glaucous beneath. Bell-shaped, soft rose-pink flowers 5cm wide, in small trusses

  • Plant range SW China

Characteristics

  • Foliage Evergreen

  • Habit Bushy

  • 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)

    H5

Colour

Sunlight

  • Partial Shade

  • Aspect South-facing or North-facing or West-facing or East-facing

  • Exposure Sheltered

Soil

  • Sand

    Sand

  • Clay

    Clay

  • Loam

    Loam

  • MoistureMoist but well-drained

  • SoilSand, Clay, Loam

  • pHAcid

Size

  • Ultimate height 1-1.5 metres

  • Ultimate spread 1-1.5 metres

  • Time to ultimate height 10-20 years

How to grow

Cultivation Grow in moist but well-drained, leafy humus-rich, acid soil. Shallow planting is essential, deep planting will not be tolerated

Propagation Propagate by seed, semi-hardwood cuttings in late summer, layering in autumn or grafting in late summer or late winter

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

How to care

Pruning Pruning group 8

Pests May be attacked by vine weevil, leafhoppers, lacebugs, scale insects, caterpillars and aphids

Diseases May be subject to powdery mildews, rhododendron petal blight, rhododendron bud blast and silver leaf

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