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Allium giganteum
  • RHS Plants for pollinators

giant onion

Bulbous perennial up to 2m in height, with spreading, glossy, pale green strap-shaped basal leaves which die down before the flowers. Dense globose umbels of lilac-pink flowers to 10cm across with prominent stamens, are borne on tall stems in summer

Other common names
giant allium
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Size
Ultimate height
1.5–2.5 metres
Time to ultimate height
2–5 years
Ultimate spread
0.1–0.5 metres
Growing conditions
Chalk
Loam
Sand
Moisture
Moist but well–drained, Well–drained
pH
Acid, Alkaline, Neutral
Colour & scent
StemFlowerFoliageFruit
Spring Green
Summer Purple Pink Green
Autumn
Winter
Position
  • Full sun
Aspect

South–facing or West–facing

Exposure
Sheltered
Hardiness
H5
Botanical details
Family
Amaryllidaceae
Native to the UK
No
Foliage
Deciduous
Habit
Clump forming
Genus

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

Name status

Correct

Plant range
C Asia to NE Iran

How to grow

Cultivation

Grow in full sun and fertile well-drained soil. It is best to grow in containers where garden soil is heavy clay and prone to saturation over winter. Ideal for cut flowers and dried flower arrangements. See allium cultivation

Propagation

Propagate by seed when just ripe or in spring; or propagate by offsets which can be carefully detached by lifting the bulb after flowering has finished. See bulb propagation

Suggested planting locations and garden types
  • Cottage and informal garden
  • City and courtyard gardens
  • Gravel garden
  • Wildlife gardens
  • Cut flowers
  • Flower borders and beds
Pruning

No pruning required, other than to remove old flowered stems and foliage

Pests

May be susceptible to allium leaf miner and onion fly

Diseases

May be susceptible to onion white rot, and onion downy mildew

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