Alnus formosana

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Synonyms

Alnus maritima var. formosana

Trees

A fast-growing deciduous tree to 20m. Leaves are green with an elongated shape, pink when young then shiny green until they fall in autumn. Male catkins hang in large numbers in spring and female woody 'cones' persist on the branches through the winter

Position

Full sun

Soil Types

Clay, Loam

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

Clay Loam
Moisture
Poorly–drained
pH
Acid or Alkaline or Neutral

Position

Full sun
Aspect
East–facing or North–facing or South–facing or West–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)
H6

Colour & Scent

Season Stem Flower Foliage Fruit
Spring
Summer
Autumn
Winter

Botanical Details

Family
Betulaceae
Native to GB/Ireland
No
Foliage
Deciduous
Habit
Spreading branched, 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
Taiwan

How to Grow

Cultivation

It is a nitrogen-fixer so can grow on poor soil. Suited to river banks on permanently damp soil in good light. For more information see tree cultivation.

Propagation

Propagate by hardwood cuttings or seed. For more advice see our information on how to propagate from seed (tree/shrub

Suggested planting locations and garden types

  • Architectural
  • Banks and slopes

Pruning

Pruning group 1

Pests

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

Diseases

May be susceptible to phytophthora root rot and honey fungus