• 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

Ceanothus arboreus 'Trewithen Blue'

Californian lilac 'Trewithen Blue'

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
Californian lilac 'Trewithen Blue'

© RHS 2002

  • Other common names Californian lilac 'Trewithen Blue'

  • Family Rhamnaceae

  • Genus Ceanothus can be evergreen or deciduous shrubs or small trees, with simple leaves and small blue, pink or white flowers in profuse axillary or terminal clusters. They are fast-growing but may be short-lived

  • Details 'Trewithen Blue' is a large vigorous evergreen spreading shrub to 6m in height, with broadly oval or rounded leaves to 8cm in length, and slightly fragrant deep blue flowers in panicles to 12cm in length

Characteristics

  • Foliage Evergreen

  • Habit Bushy

  • Fragrance Flower

  • 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)

    H4

Colour

Sunlight

  • Full Sun

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

  • Exposure Sheltered

Soil

  • Loam

    Loam

  • Clay

    Clay

  • Sand

    Sand

  • MoistureWell-drained, Moist but well-drained

  • SoilLoam, Clay, Sand

  • pHAlkaline, Neutral

Size

  • Ultimate height 4-8 metres

  • Ultimate spread 4-8 metres

  • Time to ultimate height 10-20 years

How to grow

Cultivation Grow in well-drained soil in a sheltered position in full sun

Propagation Propagate by semi-hardwood cuttings

Suggested planting locations and garden types Wall-side Borders City & Courtyard Gardens

How to care

Pruning Pruning group 8

Pests Can get scale insects

Diseases May be affected by honey fungus and Phytophthora root disease

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