• 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

Alnus glutinosa 'Imperialis'

alder 'Imperialis'

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
alder 'Imperialis'

© RHS 2002

  • Other common names alder 'Imperialis'

  • Family Betulaceae

  • Genus Alnus are vigorous deciduous trees and large shrubs with rounded leaves and often conspicuous catkins in winter

  • Details 'Imperialis' is a slow-growing medium-sized tree of conical outline and elegant habit, the leaves deeply pinnately lobed. Male catkins purplish, fruits small, cone-like

Characteristics

  • Foliage Deciduous

  • Habit Columnar/Upright

  • 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)

    H6

Colour

Sunlight

  • Full Sun

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

  • Exposure Sheltered or Exposed

Soil

  • Chalk

    Loam

  • Chalk

    Chalk

  • Chalk

    Clay

  • MoistureMoist but well-drained, Poorly-drained

  • SoilLoam, Chalk, Clay

  • pHAcid, Alkaline, Neutral

Size

  • Ultimate height Higher than 12 metres

  • Ultimate spread 4-8 metres

  • Time to ultimate height 20-50 years

How to grow

Cultivation This genus is noted for its ability to thrive in poor, wet conditions and is widely used in land reclamation

Propagation Propagate by seed or hardwood cuttings

Suggested planting locations and garden types Low Maintenance

How to care

Pruning Pruning group 1

Pests Can get alder sucker and leaf-mining sawflies

Diseases Susceptible to Phytophthora

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