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AGM plants have been through a rigorous trial and assessment programme. They are:
This plant will provide nectar and pollen for bees and the many other types of pollinating insects.
It is included in an evolving list of plants carefully researched and chosen by RHS experts. Divided into 3 groups these lists, linked below, are maintained by a team of RHS staff and are reviewed annually.
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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
Foliage Deciduous
Habit Columnar/Upright
Fragrance Foliage
Hardiness
All ratings refer to the UK growing conditions unless otherwise stated. Minimum temperature ranges (in degrees C) are shown in brackets
H5
Full Sun
Aspect South-facing or North-facing or East-facing or West-facing
Exposure Sheltered
Chalk
Clay
Loam
Sand
MoistureMoist but well-drained, Well-drained
SoilChalk, Clay, Loam, Sand
pHAcid, Alkaline, Neutral
Ultimate height 1-1.5 metres
Ultimate spread 0.1-0.5 metres
Time to ultimate height 2-5 years
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
Pruning No pruning required
Pests Generally pest free
Diseases Generally trouble-free: Onion white rot and a downy mildew may occur
RHS members can get exclusive individual advice from the RHS Gardening Advice team.
giant onion
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