Acer japonicum 'Ō-isami'

RHS Plant Profile

downy Japanese maple 'Ō-isami'

Synonyms

Acer japonica 'Ohisami'

Trees

Round-topped, deciduous tree about 7-8m tall, with sturdy, thick branches and twigs, and 9-11 lobed leaves to 20cm across, with tapered ends deeply notched. Young leaves are pale yellow-green, maturing to a rich green that lasts to autumn when they take on fiery tones of red, yellows and scarlet. Inconspicuous red-purple flowers in spring may be followed by winged, red fruits

Position

Full sun, Partial shade

Soil Types

Clay, Sand, Loam

Max Height

4-8 metres

Max Spread

2.5-4 metres

Size

Time to Maturity: 10–20 years
Max Spread: 2.5-4 metres
Max Height: 4-8 metres

Growing Conditions

Clay Sand Loam

Moisture: Moist but well–drained
pH: Acid or Alkaline or Neutral

Position

Full sun Partial shade

Aspect: East–facing or North–facing or West–facing
Exposure: 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: Sapindaceae
Native to GB/Ireland: No
Foliage: Deciduous
Habit: Bushy
Genus: Acer can be deciduous trees or large shrubs with paired, often palmately-lobed leaves and small flowers followed by characteristic winged fruits. Many have fine autumn colour, and some have ornamental stems
Name Status: Accepted

How to Grow

Cultivation

Grow in any moisture-retentive, well-drained soil in a sheltered position. Leaf colour is best in partial shade, although full sun can be tolerated if soil is reliably moist. Leaf scorch can be caused by lack of soil moisture or excessive exposure. See Japanese maples cultivation

Propagation

Propagate by layering in autumn, grafting in late winter or softwood cuttings

Suggested planting locations and garden types

Cottage and informal garden
Wildlife gardens

Pruning

Very little to no pruning required. For more advice refer to pruning group 1.

Pests

May be susceptible to Acer gall mite, aphids, caterpillars and horse chestnut scale

Diseases

May be susceptible to Verticillium wilt, acer leaf scorch and honey fungus