• 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

Symphyotrichum lateriflorum var. horizontalis

horizontal calico aster

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
horizontal calico aster

© RHS

  • Other common names horizontal calico aster

  • Synonyms Aster lateriflorus 'Horizontalis'
    Aster lateriflorus var. horizontalis

  • Family Asteraceae

  • Genus Symphyotrichum includes around 90 species of annuals and perennials, mostly spread through America, that were formerly included within the genus Aster. The Michaelmas daisies are the most widely cultivated

  • Details 'Horizontalis' is a compact herbaceous perennial with small, narrow leaves and wide-spreading branched sprays bearing tiny white-rayed flowers with reddish centres

  • Plant range N America

Characteristics

  • Foliage Deciduous

  • 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)

    H7

Colour

Sunlight

  • Full Sun

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

  • Exposure Exposed

Soil

  • Chalk

    Sand

  • Chalk

    Chalk

  • Chalk

    Loam

  • MoistureWell-drained

  • SoilSand, Chalk, Loam

  • pHAcid, Alkaline, Neutral

Size

  • Ultimate height 0.1-0.5 metres

  • Ultimate spread 0.1-0.5 metres

  • Time to ultimate height 2-5 years

How to grow

Cultivation Grow in moderately fertile, well-drained soil in open sunny position; may need staking

Propagation Propagate by division in spring

Suggested planting locations and garden types Flower borders and beds Coastal Cottage & Informal Garden Wildlife Gardens

How to care

Pruning Cut back in late autumn

Pests Generally pest free

Diseases Asters may suffer Verticillium wilt, powdery mildews and grey moulds

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