Hydrangea macrophylla Black Steel Blue ('Klazu'PBR) (Black Steel Series) (H)

Synonyms

Hydrangea macrophylla 'Klazu'^PBR

Shrubs

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A deciduous shrub to 1.2m high with broadly oval, toothed mid green leaves and striking near-black stems. Dome-shaped clusters of pale blue flowers are produced from lime green buds in summer. Colours may vary depending on the pH of the soil; blue flower colour is best maintained in acidic soils

Position

Full sun, Partial shade

Soil Types

Clay, Loam

Max Height

1-1.5 metres

Max Spread

0.1-0.5 metres

Size

Time to Maturity: 2–5 years
Max Spread: 0.1-0.5 metres
Max Height: 1-1.5 metres

Growing Conditions

Clay Loam

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

Position

Full sun Partial shade

Aspect: East–facing or South–facing or West–facing
Exposure: Exposed or 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: Hydrangeaceae
Native to GB/Ireland: No
Foliage: Deciduous
Habit: Bushy
Potentially harmful: Skin allergen. Wear gloves and other protective equipment when handling. Pets (dogs, cats): Harmful if eaten. For further information and contact numbers regarding pets, see the HTA guide to potentially harmful plants
Genus: Hydrangea can be deciduous or evergreen shrubs, or self-clinging climbers, with flowers in clusters usually comprising both small fertile and more showy sterile flowers; often good autumn colour
Name Status: Trade
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: Hortensia hydrangeas (also known as mopheads) are compact bushy deciduous shrubs with broadly ovate leaves and rounded flower clusters composed almost entirely of showy sterile flowers

How to Grow

Cultivation

Grow in any moist but well-drained soil in partial shade or grow in sun if soil remains reliably moist. Improve chalky soils with organic matter to support good growth. See shrubby hydrangea cultivation for further advice

Propagation

Propagate by softwood cuttings in early summer, or hardwood cuttings in winter. As this plant is protected by Plant Breeders' Rights, any propagation should be for personal rather than commercial use

Suggested planting locations and garden types

City and courtyard gardens
Cottage and informal garden
Coastal
Flower borders and beds
Wall side borders

Pruning

See pruning group 4 for further advice and video guide

Pests

May be susceptible to aphids, scale insects, vine weevil and capsid bug

Diseases

May be susceptible to a leaf spot, powdery mildews, grey moulds (Botrytis) and honey fungus (rarely)