Quercus glauca

RHS Plant Profile

Japanese blue oak

Other common names

ring-cupped oak

Trees

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A medium-sized, evergreen tree or, more often, a large, bushy shrub. The thick, leathery foliage is dark green above, blue green below, and may have bronze or purple tones when young. Inconspicuous catkins in spring are followed by 2cm-long acorns

Position

Full sun

Soil Types

Clay, Loam, Sand

Max Height

8-12 metres

Max Spread

4-8 metres

Size

Time to Maturity: 20–50 years
Max Spread: 4-8 metres
Max Height: 8-12 metres

Growing Conditions

Clay Loam Sand

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

Position

Full sun

Aspect: East–facing or South–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): H4

Colour & Scent

Fragrance Flower

Season	Stem	Flower	Foliage	Fruit
Spring
Summer
Autumn
Winter

Botanical Details

Family: Fagaceae
Native to GB/Ireland: No
Foliage: Evergreen
Habit: Bushy
Potentially harmful: Pets (dogs): Harmful if eaten - for further information and contact numbers regarding pets, see the HTA guide to potentially harmful plants
Genus: Quercus can be deciduous or evergreen trees or shrubs, with entire, lobed or toothed leaves; flowers inconspicuous, followed by characteristic acorns; sometimes good autumn colour
Name Status: Correct
Plant Range: Japan, China

How to Grow

Cultivation

Grow in deep, fertile, well-drained soil in full sun, with shelter from cold winds and late frosts

Propagation

Propagate by seed sown in a coldframe or seedbed as soon as ripe or by grafting in mid-autumn or late winter

Suggested planting locations and garden types

Architectural
Low Maintenance

Pruning

Pruning group 1

Pests

May be susceptible to oak processionary moth, aphids, caterpillars, leaf-mining moths and oak gall wasps

Diseases

May be susceptible to powdery mildews and honey fungus