Japanese Onion (Allium thunbergii): Late-Season Blooms That Defy Frost

Japanese onion (Allium thunbergii) is the last ornamental onion to flower, sending up mop-like heads of rose-purple blossoms with orange anthers in late summer to fall. Remarkably, the flowers withstand frost and even snow, extending garden interest well into autumn.

Standout Cultivars

• ‘Ozawa’: Larger purple flower heads than the species.
• ‘Alba’: White cup-shaped florets with white stamens, yellow anthers, and green centers—a splendid contrast.

Growing Conditions

• Light: Full sun to part shade.
• Soil: Average, well-drained.

Propagation & Care

Sow seed in spring in containers or in situ. Divide clump-forming plants in spring. Watch for bulb rot in overly damp soil, onion fly, and thrips.

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