• 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 thyrsiflorus 'Mystery Blue'

Californian lilac 'Mystery 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
  • Other common names Californian lilac 'Mystery Blue'

  • Synonyms Ceanothus thyrsiflorus 'Wisley 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 'Mystery Blue' is an airy, upright to spreading bush, to 2.4m high by 3m wide. Leaves are dark green on green stems. Very floriferous, flowers blue to blue-grey, honey scented

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 West-facing or South-facing

  • Exposure Sheltered

Soil

  • Sand

    Sand

  • Loam

    Loam

  • Chalk

    Chalk

  • MoistureWell-drained

  • SoilSand, Loam, Chalk

  • pHNeutral, Acid, Alkaline

Size

  • Ultimate height 1.5-2.5 metres

  • Ultimate spread 2.5-4 metres

  • Time to ultimate height 5-10 years

How to grow

Cultivation Grow in fertile, well-drained soil in full sun, sheltered from strong, cold winds. California lilacs are lime tolerant but may become chlorotic on shallow chalk soils

Propagation Propagate by seed or propagate by semi-ripe cuttings in mid- to late summer

Suggested planting locations and garden types Wall-side Borders Flower borders and beds City & Courtyard Gardens Coastal Cottage & Informal Garden Mediterranean Climate Plants

How to care

Pruning Pruning group 8, after flowering

Pests Generally pest free

Diseases Susceptible to honey fungus

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

The Royal Horticultural Society is the UK’s leading gardening charity. We aim to enrich everyone’s life through plants, and make the UK a greener and more beautiful place.