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Trees

Alnus formosana

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

Synonyms

Alnus maritima var. formosana

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Ultimate height

Higher than 12 metres

Time to ultimate height

20–50 years

Ultimate spread

Wider than 8 metres

Clay

Loam

Moisture

Poorly–drained

pH

Acid, Alkaline, Neutral

	Stem	Flower	Foliage	Fruit
Spring
Summer
Autumn
Winter

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)

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

Get involved

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