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Allium nigrum
  • RHS Plants for pollinators

black garlic

A. nigrum is a hardy perennial bulb, up to 75cm tall, with grey-green foliage. Large, open, creamy-white flowers, with a central greenish-black ovary, form rounded clusters with a flattened top, up to 10cm across, in early summer

Other common names
broad-leaved onion
Synonyms
Allium speciosum
Allium multibulbosum
see moreAllium nigrum var. multibulbosum
Allium bauerianum
Allium monspessulanum

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Size
Ultimate height
0.5–1 metres
Time to ultimate height
2–5 years
Ultimate spread
0.1–0.5 metres
Growing conditions
Chalk
Clay
Loam
Sand
Moisture
Moist but well–drained, Well–drained
pH
Acid, Alkaline, Neutral
Colour & scent
StemFlowerFoliageFruit
Spring Green Grey Silver
Summer Cream White Green Grey Silver
Autumn
Winter
Position
  • Full sun
Aspect

West–facing or East–facing or South–facing

Exposure
Sheltered
Hardiness
H5
Botanical details
Family
Amaryllidaceae
Native to the UK
No
Foliage
Deciduous
Habit
Bushy
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
Mediterranean

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

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
  • City and courtyard gardens
  • Gravel garden
  • Architectural
  • Cottage and informal garden
  • Flower borders and beds
Pruning

No pruning required

Pests

Generally pest free

Diseases

Onion white rot and a downy mildew may occur

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