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Allium giganteum

giant onion

RHS Plant Shop from £3.99 Sold by 38 nurseries

  • Other common names giant onion
    giant allium

  • Family Alliaceae

  • 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

  • Details 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

  • Plant range C Asia to NE Iran

Characteristics

  • Foliage Deciduous

  • Habit Columnar/Upright

  • Fragrance Foliage

  • 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

Sunlight

  • Full Sun

  • Aspect South-facing or North-facing or East-facing or West-facing

  • Exposure Sheltered

Soil

  • Chalk

    Chalk

  • Clay

    Clay

  • Loam

    Loam

  • Sand

    Sand

  • MoistureMoist but well-drained, Well-drained

  • SoilChalk, Clay, Loam, Sand

  • pHAcid, Alkaline, Neutral

Size

  • Ultimate height 1-1.5 metres

  • Ultimate spread 0.1-0.5 metres

  • Time to ultimate height 2-5 years

How to grow

Cultivation Easy to grow in fertile well-drained soil. Add grit when grown in clay soils to improve drainage. See allium cultivation for further advice

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 Cut Flowers Flower borders and beds Cottage & Informal Garden

How to care

Pruning No pruning required

Pests Generally pest free

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

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RHS Plants Shop

Allium giganteum

giant onion

Buy from £3.99 at the RHS Plants Shop

Buy from £3.99 at the RHS Plants Shop

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