Common Name: ornamental onion
Type: Herbaceous perennial
Family: Amaryllidaceae
Zone: 4 to 9
Height: 0.75 to 1.00 feet
Spread: 0.50 to 0.75 feet
Bloom Time: September to October
Bloom Description: red-violet
Sun: Full sun to part shade
Water: Medium
Maintenance: Low
Flower: Showy
Leaf: Fragrant
Tolerate: Deer, Drought
Culture
Easily grown in average, medium moisture, well-drained soils in full sun to part shade. Best in full sun. Plant bulbs in fall or early spring. Plant seeds in spring.
Noteworthy Characteristics
Allium thunbergii, commonly known as Japanese onion, is a bulbous, clump-forming, ornamental onion that typically grows to 18-24” tall with a spread of 10-15”. It is native to Japan, Korea and coastal China where it is often found growing along woodland margins. Its main claim to fame is a fall bloom (September to November) of bright purple to purple-pink flowers (each with six tepals and elongated stamens) which appear in globular clusters (terminal umbels to 2 1/ 2” across) atop thin scapes. Tufts of thin, rounded, grass-like, hollow green leaves are attractive throughout the growing season. Leaves turn a showy tawny orange at frost. Leaves have a typical onion smell when bruised, but are not used for culinary purposes.
Genus name comes from the classical Latin name for garlic.
Specific epithet honors Carl Peter Thunberg (1743-1828), Swedish physician and surgeon, student of Linnaeus, naturalist, plant collector, and author of Flora Japonica (1784), who collected about 300 new plants (including the species herein) on his visit to Japan in 1775-1776.
‘Ozawa’ is more compact and floriferous with larger flower heads than those found on species plants. It typically grows to only 6-12” tall and as wide. Introduced by George Schenk in the State of Washington.
Problems
No serious insect or disease problems. If flowering decreases over time, tufts should be dug up, divided and replanted.
Uses
Group or mass in rock gardens or border fronts for enjoyment of fall bloom.