“Senshyu” onion

Senshyu Yellow Onion (Allium cepa) – Long-Keeping Heritage Variety

Botanical Name: Allium cepa
Common Name: Senshyu Yellow Onion
Heirloom | Open-Pollinated | Non-GMO | Annual (grown from seed)

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.
? Product Highlights:

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 Sensh? 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 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

? Gardener’s 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.