Rhododendron 'Oberbürgermeister Janssen'

RHS Plant Profile
rhododendron 'Mayor Johnstone'

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rhododendron 'Mayor Johnstone' RHS

Synonyms

Rhododendron Mayor Johnstone

Shrubs
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A compact, spreading evergreen shrub with pointed, matt-green foliage and clusters of bright red flowers, opening to orange red with a brown centre, appearing in late May

Position

Partial shade

Soil Types

Clay, Loam, Sand

Max Height

1-1.5 metres

Max Spread

1.5-2.5 metres

Size

Time to Maturity
10–20 years
Max Spread
1.5-2.5 metres
Max Height
1-1.5 metres

Growing Conditions

Clay Loam Sand
Moisture
Moist but well–drained
pH
Acid

Position

Partial shade
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)
H5

Colour & Scent

Season Stem Flower Foliage Fruit
Spring
Summer
Autumn
Winter

Botanical Details

Family
Ericaceae
Native to GB/Ireland
No
Foliage
Evergreen
Habit
Bushy
Potentially harmful
Harmful if eaten. Wear gloves and other protective equipment when handling. Pets (dogs, cats, rabbits, tortoises) Harmful if eaten - for further information and contact numbers regarding pets, see the HTA guide to potentially harmful plants
Genus
Rhododendron can be evergreen or deciduous shrubs or trees, with simple leaves, sometimes with a dense colourful indumentum of hairs on the lower side, and funnel-shaped, bell-shaped or tubular flowers that may be solitary or in short racemes
Name Status
Accepted

How to Grow

Cultivation

Grow in moist but well-drained, leafy, humus-rich acid soil in part shade with shelter; see rhododendron cultivation

Propagation

Propagate by semi-ripe cuttings in late summer, layering in autumn or grafting in late summer or late winter

Suggested planting locations and garden types

  • Cottage and informal garden
  • Low Maintenance
  • Banks and slopes
  • Flower borders and beds
  • Underplanting of roses and shrubs
  • Wall side borders

Pruning

Pruning group 8

Pests

May be susceptible to vine weevil, rhododendron leafhopper, pieris lacebug, scale insects, caterpillars and aphids

Diseases

May be susceptible to various Rhododendron diseases including powdery mildews, rhododendron petal blight, rhododendron bud blast, silver leaf and honey fungus