Senshyu Yellow Onion (Allium cepa)

Botanical Name: Allium cepa
Common Name: Senshyu Yellow Onion
Heirloom | Open-Pollinated | Non-GMO

Senshyu is a traditional Japanese onion variety, prized for its excellent storage life, mild-sweet flavor, and strong, golden bulbs. Though originally bred as an overwintering onion, it performs exceptionally well when sown in early spring in Irish and cool temperate climates, maturing into a dependable, long-keeping crop by midsummer.

Horticultural Points

• Bulb Size: Medium to large, flat-round shape
• Skin: Deep golden-brown with tight, protective wrappers
• Flesh: Crisp white, mild to semi-sweet flavor
• Storage: Excellent – stores 4 to 6 months when cured properly
• Days to Maturity: ~150–170 days from seed
• Growing Season: Spring-sown for midsummer harvest and winter storage

Historical Background & Japanese Origin

• The Senshyu onion originates from the Senshyu region of southern Osaka Prefecture, Japan, an area with a long tradition of winter vegetable farming.
• Developed in the early 20th century, Senshyu was bred by crossing European onions, introduced to Japan during the Meiji Era, with local cultivars to create a variety that could withstand the cold and mature early in the season.
• While originally cultivated as an autumn-sown overwintering crop, Senshyu adapted well to spring sowing in northern climates.
• Its early maturity, reliable performance, and excellent storage qualities led to its spread beyond Japan, where it gained popularity in Europe, the UK, and Ireland, particularly among heritage seed growers and self-sufficient gardeners.

Growing Information

• Sow Indoors: Late winter to early spring (February–March)
• Transplant: When the soil is workable (March–April)
• Spacing: 10–15 cm apart in rows 25–30 cm apart
• Sunlight: Full sun
• Soil Needs: Fertile, well-drained soil rich in organic matter
• Watering: Moderate, especially in dry spells; reduce before harvest
• Harvest: Late July to early August, when tops fall over
• Curing: Dry bulbs in a warm, airy space for 2–3 weeks before storing

Gardening Tip

• For best bulb size and storage life, keep the beds weed-free, feed with a potassium-rich organic fertilizer during bulb formation, and ensure proper curing before storage.