Hydrangea serrata 'Shiro-gaku' (L)

RHS Plant Profile
hydrangea 'Shiro-gaku'

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A compact, deciduous shrub up to 1.2m high and wide, with mid-green foliage and producing lacecap heads with small green fertile flowers, surrounded by large, white, double sterile florets, in early summer

Position

Partial shade

Soil Types

Clay, Loam, Sand

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 Sand
Moisture
Moist but well–drained
pH
Acid or Neutral

Position

Partial shade
Aspect
East–facing or North–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)
H4

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
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

Lace cap hydrangeas are compact deciduous shrubs with broadly ovate leaves and flat or gently domed clusters of small fertile flowers, with showy sterile flowers around the margin

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

For home use, propagate by softwood cuttings in early summer or hardwood cuttings in winter

Suggested planting locations and garden types

  • City and courtyard gardens
  • Coastal
  • Cottage and informal garden
  • Flower borders and beds

Pruning

Pruning group 4

Pests

May be susceptible to aphids, capsid bug and hydrangea scale

Diseases

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