Allium sphaerocephalon

RHS Plant Profile
round-headed leek

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round-headed leek RHS
round-headed leek RHS

Other common names

round-headed garlic

Synonyms

Allium cilicicum misapplied
Allium descendens

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A tall perennial with a tuft of narrow basal leaves to 30cm long, and long-stalked, dense, rounded heads of pink or reddish-brown flowers in summer

Position

Full sun

Soil Types

Chalk, Clay, Loam, Sand

Max Height

0.5-1 metres

Max Spread

0.1-0.5 metres

Size

Time to Maturity
2–5 years
Max Spread
0.1-0.5 metres
Max Height
0.5-1 metres

Growing Conditions

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

Position

Full sun
Aspect
South–facing or North–facing or West–facing or East–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)
H6

Colour & Scent

Fragrance Foliage
Season Stem Flower Foliage Fruit
Spring
Summer
Autumn
Winter

Botanical Details

Family
Amaryllidaceae
Native to GB/Ireland
Yes
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
Eurasia, Africa

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

  • City and courtyard gardens
  • Coastal
  • Cottage and informal garden
  • Patio and container plants
  • Flower borders and beds

Pruning

No pruning required

Pests

Generally pest-free

Diseases

May be susceptible to onion white rot and downy mildews