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Allium unifolium
  • RHS AGM
  • RHS Plants for pollinators

American onion

A compact perennial to 30cm in height, with short grey-green basal leaves and umbels of relatively large, star-shaped rose-pink flowers in late spring

Synonyms
Allium grandisceptrum
Allium murrayanum misapplied
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Size
Ultimate height
0.1–0.5 metres
Time to ultimate height
2–5 years
Ultimate spread
0–0.1 metre
Growing conditions
Chalk
Clay
Loam
Sand
Moisture
Moist but well–drained, Well–drained
pH
Acid, Alkaline, Neutral
Colour & scent
StemFlowerFoliageFruit
Spring Pink Green Grey Silver
Summer Green Grey Silver
Autumn
Winter
Position
  • Full sun
Aspect

South–facing or West–facing or East–facing or North–facing

Exposure
Sheltered
Hardiness
H5
Botanical details
Family
Amaryllidaceae
Native to the UK
No
Foliage
Deciduous
Habit
Columnar upright
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
USA Oregon to W California

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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 seeds in containers with bottom heat when ripe and grow on under glass. Remove offsets in spring and grow on under glass for 2 seasons

Suggested planting locations and garden types
  • Gravel garden
  • Rock garden
  • Flower borders and beds
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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