Alnus incana

RHS Plant Profile
grey alder

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grey alder RHS
grey alder RHS

Other common names

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

Trees
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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

Position

Full sun

Soil Types

Chalk, Clay, Loam, Sand

Max Height

Higher than 12 metres

Max Spread

wider than 8 metres

Size

Time to Maturity
20–50 years
Max Spread
wider than 8 metres
Max Height
Higher than 12 metres

Growing Conditions

Chalk Clay Loam Sand
Moisture
Moist but well–drained or Poorly–drained or Well–drained
pH
Acid or Alkaline or Neutral

Position

Full sun
Aspect
North–facing or West–facing or East–facing or South–facing
Exposure
Exposed or 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)
H7

Colour & Scent

Season Stem Flower Foliage Fruit
Spring
Summer
Autumn
Winter

Botanical Details

Family
Betulaceae
Native to GB/Ireland
No
Foliage
Deciduous
Habit
Columnar upright
Genus
Alnus are vigorous deciduous trees and large shrubs with rounded leaves and often conspicuous catkins in winter
Name Status
Correct
Plant Range
Europe, Caucasus

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

  • Coastal
  • Cottage and informal garden
  • Wildlife gardens

Pruning

Pruning group 1 between leaf fall and midwinter

Pests

May be susceptible to alder sucker, alder leaf beetle and leaf-mining sawflies

Diseases

May be susceptible to Phytophthora and honey fungus