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Allium giganteum

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© RHS 1999

Characteristics

Plant type

Bulb

Habit

Columnar/Upright

Fragrance

Leaf

Toxicity

Resilience

Hardiness

old H4 (hardy)

Colour

Flower

Purple in Summer

Foliage

Green in Spring

Size

Ultimate height

1-1.5 metres

Ultimate spread

0.1-0.5 metres

Time to ultimate height

2-5 years


Preferred common name

giant onion

Family

Alliaceae


Allium are bulbous herbaceous perennials with a strong onion or garlic scent, linear, strap-shaped or cylindrical basal leaves and star-shaped or bell-shaped flowers in an umbel on a leafless stem

A. giganteum is a perennial with spreading, glossy, strap-shaped basal leaves which die down before the flowers. Dense globose umbels of bright purple flowers are borne on tall stems in summer

Other common names

  • giant allium

How to grow

Sunlight

  • Full sun

Aspect

  • South-facing, North-facing, West-facing or East-facing
  • Sheltered

Cultivation

Easy to grow in fertile well-drained soil. Add grit when grown in clay soils to improve drainage

Soil

  • Well-drained or Moist but well-drained
  • Acid, Alkaline or Neutral
  • Chalk, Clay, Sand or Loam

Propagation

Propagate by seed, sowing in containers in a cold frame when just ripe or in the spring. Alternatively, remove offsets in autumn

Suggested planting locations and garden types

Cottage/Informal Garden, Flower borders and beds or Cut Flowers


How to care

Pruning

No pruning required

Pests

Generally pest free

Diseases

Generally trouble-free: Onion white rot and a downy mildew may occur