Quercus robur 'Irtha'

RHS Plant Profile

common oak 'Irtha'

Trees

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A very unusual form of small deciduous tree, slowly reaching approximately 10m. The leaves are much reduced and a bit twisted, giving a kind of ribbony appearance. They form clusters at the branch ends which, with the fresh yellow-green leaves in spring, look a bit like blossom. The real flowers are inconspicuous but become acorns which show clearly amongst the leaves.

Position

Full sun

Soil Types

Chalk, Clay, Loam, Sand

Max Height

8-12 metres

Max Spread

4-8 metres

Size

Time to Maturity: 10–20 years
Max Spread: 4-8 metres
Max Height: 8-12 metres

Growing Conditions

Chalk Clay Loam Sand

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

Position

Full sun

Aspect: East–facing or North–facing or South–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: Fagaceae
Native to GB/Ireland: No
Foliage: Deciduous
Habit: Spreading branched
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: Accepted

How to Grow

Cultivation

Suited to small-medium gardens. Grows in any well-drained but moisture-retentive soil in good light. For more information see tree cultivation.

Propagation

Propagate by hardwood cuttings in autunm

Suggested planting locations and garden types

Architectural

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