How big does Round-headed leek grow?

About 80 cm × 15 cm after ten years (height × width).

What soil does Round-headed leek grow in?

It tolerates these soils: average garden soil, clay, sandy, calcareous.

Is Round-headed leek hardy?

Hardy down to -29 °C (USDA zone 4, RHS H7). It gets through winter in every part of the country.

When does Round-headed leek flower?

Flowering: June–August, purple, red.

How much water does Round-headed leek need?

Water need: low. Drought tolerance: high.

Round-headed leek

Allium sphaerocephalon

Round-headed leek (Allium sphaerocephalon) is a perennial that reaches 80 cm × 15 cm after ten years. Light: full sun, part shade. Hardy down to -29 °C. Drought tolerance: high. Toxic to dogs and cats.

Illustration of Round-headed leek — An illustration of the typical shape of the mature plant, not a photo.

What it's good for, and what it isn't

Round-headed leek flowers in midsummer, after most ornamental onions have finished: slim, upright stems carry small egg-shaped heads that open green and turn reddish purple from the top down, and bees and butterflies love them. Plant the bulbs in autumn about 10 cm deep, closely in larger groups or scattered among perennials and grasses, in a sunny, well-drained spot; it is very happy in dry, limy soil, and in heavy ground a bed of grit under the bulbs helps. Wild populations are protected in many places, so only plant bulbs bought from a nursery.

Watch out for

In wet, waterlogged soil the bulbs rot, so in heavy ground plant them only over a layer of grit or sand. Onion white rot, downy mildew, powdery mildew, rust and leaf spots can occur, less often thrips and bulb mites. If you do not cut off the spent heads it self-seeds freely and forms large patches over time.

Key facts

Light: Full sun, Part shade
Water need: Low
Care: Low
Size after 10 years: 80 cm × 15 cm
Hardiness: down to -29 °C
Foliage: Deciduous
Flowering: J F M A M J J A S O N D June–August, purple, red

Group	Perennial
Light	Full sun, Part shade
Size after 10 years	80 cm × 15 cm
Ultimate size	50–90 cm × 10–45 cm
Hardiness	down to -29 °C (USDA 4, RHS H7)
Soil	Average garden soil, Clay, Sandy, Calcareous
Foliage	Deciduous
Flowering	June–August, purple, red
Water need	Low
Drought tolerance	High
Maintenance	Low
Root aggressiveness	Low
Suckering	no data
Spreading	Medium
Distance from buildings	no data
Distance from paving	no data
Litter	not typical
Planting distance	10 cm
For dogs	Toxic
For cats	Toxic
For children	Mildly toxic (uncertain)
Typical price	no data

Toxicity data is for information only. If your pet or child has eaten a plant, contact a vet or a doctor.

Frequently asked questions

Data updated: October 19, 2026 · How our data is made

Appears in these lists

Perennials for part shade Perennials for full sun Perennials that flower all summer Drought-tolerant plants Drought-tolerant perennials Drought-tolerant plants for sandy soil Perennials for clay soil Perennials for pollinators Low-maintenance perennials Plants for a Mediterranean garden

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