• AGM plants

    AGM plants have been through a rigorous trial and assessment programme. They are:

    • Excellent for ordinary use in appropriate conditions
    • Available to buy
    • Of good constitution
    • Essentially stable in form & colour
    • Reasonably resistant to pests & diseases

Quercus robur (Fastigiata Group) 'Koster'

oak 'Koster'

AGM plants

AGM plants have been through a rigorous trial and assessment programme. They are:

  • Excellent for ordinary use in appropriate conditions
  • Available to buy
  • Of good constitution
  • Essentially stable in form & colour
  • Reasonably resistant to pests & diseases
oak 'Koster'

© RHS

  • Other common names oak 'Koster'

  • Synonyms Quercus robur f. fastigiata 'Koster' AGM
    Quercus robur 'Fastigiata Koster'

    Quercus robur 'Kosteri Fastigiata'

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  • Family Fagaceae

  • 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

  • Details 'Koster' is a fastigiate form with upright branches, spreading with age to ultimately reach 15m high and wide. Usually seed-raised so can be variable. Leaves are dark green with shallow lobes

Characteristics

  • Foliage Deciduous

  • Habit Columnar/Upright

  • 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

Sunlight

  • Full Sun

  • Partial Shade

  • Aspect North-facing or East-facing or South-facing or West-facing

  • Exposure Sheltered or Exposed

Soil

  • Sand

    Sand

  • Clay

    Clay

  • Loam

    Loam

  • MoistureWell-drained, Moist but well-drained

  • SoilSand, Clay, Loam

  • pHAcid, Neutral, Alkaline

Size

  • Ultimate height Higher than 12 metres

  • Ultimate spread wider than 8 metres

  • Time to ultimate height more than 50 years

How to grow

Cultivation Grows well in most deep, fertile soils and is lime tolerant

Propagation Propagate by seed, sown as soon as ripe, in a cold frame

Suggested planting locations and garden types Low Maintenance Cottage & Informal Garden

How to care

Pruning Pruning group 1

Pests Susceptible to aphids, caterpillars, leaf-mining moths and oak gall wasps

Diseases May be affected by powdery mildews. Also oak wilt in USA only

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