Ceanothus thyrsiflorus 'Cool Blue'

RHS Plant Profile
Californian lilac 'Cool Blue'

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An upright, evergreen variegated shrub to 1.2m with arching branches and small, glossy, mid-green leaves with creamy white margins. Bears clusters of tiny, pale to dark blue flowers in spring

Position

Full sun

Soil Types

Loam, Sand

Max Height

1.5-2.5 metres

Max Spread

1.5-2.5 metres

Size

Time to Maturity
5–10 years
Max Spread
1.5-2.5 metres
Max Height
1.5-2.5 metres

Growing Conditions

Loam Sand
Moisture
Well–drained
pH
Alkaline or Neutral or Acid

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)
H4
Drought Resistance
Yes

Colour & Scent

Season Stem Flower Foliage Fruit
Spring
Summer
Autumn
Winter

Botanical Details

Family
Rhamnaceae
Native to GB/Ireland
No
Foliage
Evergreen
Habit
Bushy
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
Name Status
Accepted

How to Grow

Cultivation

Grow in fertile, well-drained soil in full sun with shelter from strong, cold winds. Lime tolerant but may become chlorotic on shallow chalk soils. See ceanothus cultivation

Propagation

Propagate by semi-hardwood cuttings in mid- to late summer

Suggested planting locations and garden types

  • City and courtyard gardens
  • Coastal
  • Cottage and informal garden
  • Mediterranean climate plants
  • Wildlife gardens
  • Wall side borders

Pruning

Pruning group 8, after flowering

Pests

May be susceptible to scale insects

Diseases

May be susceptible to honey fungus and phytophthora root disease