Allium nigrum

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black garlic

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black garlic RHS
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Other common names

broad-leaved onion

Synonyms

Allium speciosum
Allium multibulbosum
Allium nigrum var. multibulbosum
Allium bauerianum
Allium monspessulanum

Plants for pollinators
Bulbs
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Bulbous perennial about 40cm or more tall, with lance-shaped, grey-green basal leaves to 50cm long. Open, cup-shaped creamy-white flowers, occasionally lilac, with a central greenish-black ovary, form rounded clusters with a flattened top, up to 7cm across, in early summer

Position

Full sun

Soil Types

Chalk, Loam, Sand

Max Height

0.5-1 metres

Max Spread

0.1-0.5 metres

Size

Time to Maturity
1–2 years
Max Spread
0.1-0.5 metres
Max Height
0.5-1 metres

Growing Conditions

Chalk Loam Sand
Moisture
Moist but well–drained or Well–drained
pH
Acid or Alkaline or Neutral

Position

Full sun
Aspect
West–facing or South–facing
Exposure
Sheltered
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 & Scent

Fragrance Foliage
Season Stem Flower Foliage Fruit
Spring
Summer
Autumn
Winter

Botanical Details

Family
Amaryllidaceae
Native to GB/Ireland
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
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
  • Cottage and informal garden
  • Patio and container plants
  • Wildlife gardens
  • Flower borders and beds
  • Cut flowers

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