Rhododendron 'Olga Niblett' (EA) | rhododendron 'Olga Niblett'

Shrubs

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An evergreen azalea to about 1.5m high, with an upright habit and broadly elliptic dark green leaves. Produces double (hose-in-hose) white flowers, with bright yellow-green spots on the petals, in late spring. A Robin Hill hybrid, part of a collection bred in the USA around the 1940s and 50s, to improve the hardiness of the larger flowered Satsuki hybrids

Position

Partial shade

Soil Types

Clay, Loam

Max Height

1-1.5 metres

Max Spread

1-1.5 metres

Size

Time to Maturity: 5–10 years
Max Spread: 1-1.5 metres
Max Height: 1-1.5 metres

Growing Conditions

Clay Loam

Moisture: Moist but well–drained
pH: Acid

Position

Partial shade

Aspect: 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): H6

Colour & Scent

Season	Stem	Flower	Foliage	Fruit
Spring
Summer
Autumn
Winter

Botanical Details

Family: Ericaceae
Native to GB/Ireland: No
Foliage: Evergreen
Habit: Columnar upright
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, acidic soil, in partial or dappled shade. Choose a site away from frost pockets and sheltered from strong winds. Mulch annually, ideally with leaf mould. See rhododendron cultivation for more detailed advice

Propagation

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

Suggested planting locations and garden types

City and courtyard gardens
Cottage and informal garden
Patio and container plants
Flower borders and beds
Wall side borders

Pruning

Minimal pruning required, see pruning group 8 (evergreens). Deadhead if practical, to promote vegetative growth rather than seed production

Pests

May be susceptible to vine weevil, rhododendron and azalea whitefly, rhododendron leafhopper, Pieris lacebug, scale insects, caterpillars and aphids

Diseases

May be susceptible to powdery mildews, honey fungus, silver leaf and Phytophthora, as well as more specific Rhododendron diseases