Allium sphaerocephalum (Onion, Flowering) — Upright bare stems from a bulb

Overview

Allium sphaerocephalum is a upright bare stems from a bulb bulb in the genus Allium, part of the Amaryllidaceae family, with deciduous; strap-shaped or grassy basal leaves, dying back as the flowers open foliage. Allium sphaerocephalum grows best in full sun, and tolerates most soils and neutral to alkaline pH. Its UK hardiness is rated H4-H6. It is native to Belgium, Brussels-Capital Region, Flemish Region and Walloon Region.

About

Allium sphaerocephalum is a bulbous perennial in the Amaryllidaceae that sends upright, bare stems from a bulb to carry its flowers. It produces strap-shaped basal leaves that die back as the flowers open. Flowering occurs May to July. Plants prefer full sun on light, free-draining loam, sand or chalk with neutral to alkaline soil.

Wikipedia contributors, CC BY-SA 4.0 — Allium sphaerocephalon

About the genus

Allium is a large genus of monocotyledonous flowering plants with 1112 accepted species, making Allium the largest genus in the family Amaryllidaceae and among the largest plant genera in the world. Many of the species are edible, and some have a long history of cultivation and human consumption such as the onion, garlic, scallions, shallots, leeks, and chives.

Wikipedia contributors, "Allium", CC BY-SA 4.0 — Allium

In the garden

Native to Belgium (Brussels-Capital Region, Flemish Region and Walloon Region), Allium sphaerocephalum is a bulb-forming member of the genus Allium. It develops upright, leafless flowering stems from a bulb, with deciduous, strap-shaped basal leaves that die back as the bloom period begins. Sit bulbs in full sun in light, free-draining soils such as loam, sand or chalk and aim for a neutral to alkaline pH. Good drainage is essential because bulbs will rot in persistently wet ground; the species tolerates exposed or sheltered sites and favours a south- or west-facing aspect. Hardiness is H4–H6, giving average to very hardy performance across much of the UK. In the garden it works well where tall, bare scapes are acceptable — sunny borders, gravel or well-drained beds. Leave the strap-shaped basal leaves in place until they have died back, so the bulbs can replenish for the next season.

Growing conditions

Best soil and position for Allium

Sunlight: Full sun
Soil type: Light, free-draining loam, sand or chalk
Soil pH: Neutral to alkaline
Soil moisture: Well drained; bulbs rot in wet ground
Aspect: South or west facing
Exposure: Exposed or sheltered
UK hardiness: H4-H6

Plant details

Allium sphaerocephalum size, habit and characteristics

Plant type: Bulb
Habit: Upright bare stems from a bulb
Foliage: Deciduous; strap-shaped or grassy basal leaves, dying back as the flowers open
Native to: Belgium, Brussels-Capital Region, Flemish Region, Walloon Region

Care notes

Pruning and caring for Allium sphaerocephalum

Cultivation: Plant bulbs in autumn at roughly three times their depth in the sunniest, best-drained ground available; on heavy soil add grit beneath the bulb. Site them behind or among lower perennials, since the foliage yellows and collapses just as the heads open. Leave the leaves to die down completely rather than removing them, and most kinds will bulk up and self-seed steadily.
Pruning: Leave the seedheads standing - they are among the best structural remains in a late-summer border - and cut the stems at the base only once they finally break down.
Propagation: Separate offsets when the bulbs are dormant in late summer. Species come readily from seed but take two to four years to flower, and many self-sow generously.
Pest resistance: Allium leaf miner and onion fly can affect the larger-bulbed kinds; otherwise little troubled.
Disease resistance: White rot and downy mildew occur in wet ground or where alliums have been grown repeatedly on the same site.

Frequently asked questions

How do I grow Allium sphaerocephalum?

Plant bulbs in autumn at roughly three times their depth in the sunniest, best-drained ground available; on heavy soil add grit beneath the bulb. Site them behind or among lower perennials, since the foliage yellows and collapses just as the heads open. Leave the leaves to die down completely rather than removing them, and most kinds will bulk up and self-seed steadily.

Where is the best place to plant Allium sphaerocephalum?

Allium sphaerocephalum prefers full sun. It suits exposed or sheltered positions.

What soil does Allium sphaerocephalum need?

Allium sphaerocephalum is adaptable and grows happily in most soil types, including light, free-draining loam and sand or chalk. It prefers neutral to alkaline soil. Aim for soil that stays well drained; bulbs rot in wet ground.

How do I prune Allium sphaerocephalum?

Leave the seedheads standing - they are among the best structural remains in a late-summer border - and cut the stems at the base only once they finally break down.

Is Allium sphaerocephalum hardy in the UK?

Allium sphaerocephalum has an RHS hardiness rating of H4, meaning it is hardy through an average UK winter, tolerating -10 to -5°C.

How do I propagate Allium sphaerocephalum?

Separate offsets when the bulbs are dormant in late summer. Species come readily from seed but take two to four years to flower, and many self-sow generously.

More in the Allium genus

Browse all Allium →