• 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 incana

grey alder

  • Other common names grey alder
    gray alder

    American black alder
    common black alder
    hoary-leaved alder
    speckled alder

    see more
  • Family Betulaceae

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

  • Details A. incana is a conical tree, to 20m, with dark-green leaves to 10cm long, grey-white and hairy beneath. Yellow-brown male catkins in pendent clusters of 3 or 4 are produced in late winter or early spring, before the leaves. Ovoid fruit is produced in summer

  • Plant range Europe, Caucasus

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)

    H7

Colour

Sunlight

  • Full Sun

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

  • Exposure Sheltered or Exposed

Soil

  • Loam

    Loam

  • Chalk

    Chalk

  • Clay

    Clay

  • Sand

    Sand

  • MoistureMoist but well-drained, Poorly-drained, Well-drained

  • SoilLoam, Chalk, Clay, Sand

  • pHAcid, Alkaline, Neutral

Size

  • Ultimate height Higher than 12 metres

  • Ultimate spread wider than 8 metres

  • Time to ultimate height 20-50 years

How to grow

Cultivation Grow in moderately fertile, moist but well-drained soil in full sun or part shade. Noted for its ability to thrive in poor, wet conditions but is also tolerant of dry soils

Propagation Propagate by seed or hardwood cuttings

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

How to care

Pruning Pruning group 1 between leaf fall and midwinter

Pests May be affected by alder sucker, alder leaf beetle and leaf-mining sawflies

Diseases Susceptible to Phytophthora

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.