Rhododendron 'Mary Helen' (Glenn Dale) (EA)

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azalea 'Mary Helen'

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A spreading evergreen shrub with glossy green, small leaves and large, white flowers with a wavy margin up to 5cm across with a yellow spotting and dark anthers, produced in early June.

Position

Partial shade

Soil Types

Clay, Loam, Sand

Max Height

0.5-1 metres

Max Spread

1-1.5 metres

Size

Time to Maturity
5–10 years
Max Spread
1-1.5 metres
Max Height
0.5-1 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
Spreading branched
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
Horticultural Group

Horticultural Classification Codes

Horticultural Classification Codes are often given to genera which have a large number of species or cultivars. They are used to categorise cultivated plants based on specific, shared characteristics such as shape, colour, size or flowering time, and can be displayed as letters or numbers

For example:
Dahlia ‘Sunset Kate (Sin) = Single flower
Rosa ‘Marigold’ (HT) = Hybrid Tea

Evergreen azaleas are compact evergreen shrubs with small leaves and terminal racemes of small, funnel-shaped, usually unscented flowers in early summer

How to Grow

Cultivation

Grow in moist but well-drained, humus rich acid soil in a sheltered position in part shade; see rhododendron cultivation

Propagation

Propagate by semi-ripe cuttings in late summer

Suggested planting locations and garden types

  • City and courtyard gardens
  • Cottage and informal garden
  • Patio and container plants
  • Low Maintenance

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 mildew, rhododendron petal blight, rhododendron bud blast, silver leaf and honey fungus