Know Before You Go: Information and helpful hints for your next visit
The Morton Arboretum Get tickets
Browse Trees and Plants

Thunberg's onion

Allium thunbergii

Common names:
Thunberg's onion, Japanese onion, Thunberg's allium

Content Detail

Thunberg’s onion is a compact, clump-forming, perennial bulb that adds seasonal interest in the late fall garden. Clusters of lavender-pink flowers open above the grass-like foliage in late summer blooming into fall when the leaves turn a rusty orange color.

  • Family (English) Amaryllis
  • Family (botanic) Amaryllidaceae
  • Tree or plant type Perennial
  • Native locale Non-native
  • Size range Medium plant (12-24 inches), Large plant (more than 24 inches)
  • Light exposure Full sun (6 hrs direct light daily), Partial sun / shade (4-6 hrs light daily)
  • Hardiness zones Zone 4, Zone 5 (Northern Illinois), Zone 6 (City of Chicago), Zone 7, Zone 8, Zone 9
  • Soil preference Moist, well-drained soil
  • Tolerances Alkaline soil, Dry sites, Occasional drought
  • Season of interest mid fall, late fall
  • Flower color and fragrance Pink, Purple
  • Shape or form Upright
  • Growth rate Fast

Size: 

Thunberg’s onion is a clump-forming, perennial bulb with narrow foliage reaching 12 to15 inches high.

Native geographic location and habitat: 

Found along wood edges of Japan, Korea, and China.

Attracts birds or pollinators: 

Butterflies, hummingbirds, bees, and other pollinators are attracted to the flowers.

Leaf description: 

The onion-scented, grass-like hollow leaves tend to relax on the ground before flowers emerge. Leaves turn a rusty-orange after the first frost.

Flower description: 

Terminal umbels of nodding flower clusters open to purplish-pink flowers with protruding yellow-orange stamens. This is one of the last onions to flower in the fall.

Fruit description: 

Because flowers appear so late in the fall, plants rarely produce seeds

Plant care:

Thunberg’s onion prefers full sun to part shade and  well-drained soil. Divide clumps in early spring, just as new foliage is emerging.

List of pests, diseases, and tolerances: 

None serious. Does not tolerate wet soils. Tolerant of deer, rabbit, black walnut toxicity.

White Thunberg’s onion (Allium thunbergii ‘Alba’): 

This cultivar is 12 to 15 inches high, with white flowers.

Ozawa Thunberg’s Onion (Allium thunbergii ‘Ozawa’):

Compact mounds of 6 to 12 inch high foliage support pinkish-purple flowers.

Photo Gallery (1)

Slider

Slider

1

Donate

Your support is vital to the Arboretum, where the power of trees makes a positive impact on people’s lives.

Make a gift