Introduced to the UK from Japan in the early 70's for harvesting before the traditional spring sown bulbing varieties are ready. ‘Senshyu Yellow Globe’ was one of the first Japanese overwintering varieties to be tried and tested. Today it remains a growers favourite for surviving the winter well.
Hardy to around minus 18°C (0°F), this reliable maincrop produced heavy yields of semi-globe shaped bulbs with straw coloured skins and crisp white flesh. Growing to a height of around 45cm (18in) and a spread of 15cm (6in), it matures June to July from an August sowing. Giving onions of usable size before spring sown maincrops varieties are ready.
Overwintered onions are in the ground a lot longer than their summer counterparts - roughly 300 days. Because of this, they have more time to develop a vigorous root system, which means they grow more strongly on heavy soils. In addition, overwintering types do most of their growing during spring, when soil moisture is plentiful. They mature and dry down in early summer when the days are at their longest. All these factors add up getting larger onions with less effort.
Since these onions are ready to harvest between June and early July, the, usually dry weather we receive then is much more conducive to good curing. The newer varieties of overwintering onions will easily keep well into autumn if cured properly. So, you can have onions available year-round without too much effort.
Onion 'Senshyu Yellow' is recommended by the National Institute of Agricultural Botany.
Choose an open, sunny site with good drainage which has preferably been dug and manured in the previous autumn. Do not plant or sow on freshly manured bed. Lime if the soil is acid. Avoid planting in an area where the previous crop was of the onion family. Apply a general fertiliser if needed and rake the surface when the soil is reasonably dry. Tread over the area and then rake again to produce a fine, even tilth.
A potential problem for most overwintered alliums (including onions, scallions, and garlic) is the constant rainfall and saturated soil we experience most winters. It can be wise to grow any alliums in raised beds to improve the drainage. If you can do it, getting some sort of cover over your overwintered onions will result in less winter damage, which will translate into stronger, earlier growth the following spring.
Sowing: Sow direct or start in seed trays in August to plant out in October.
Growing overwintered onions is not difficult; the critical bit is the timing. You want to end up this autumn with onions that are small enough they won't try to flower, but big enough that they will make it through the winter and get going quickly in the spring. The ideal date for sowing is in mid August to be harvested in 46 weeks to produce large bulbs
Seeds should be sown direct in August. Sow very thinly in 12mm (½in) deep drills and 30 to 45cm (12 to 18in) between rows. Water very gently if the soil is dry, and cover with soil. Seeds will germinate in 12 to 15 days. When the plants are 15cm (6in) tall, thin the crop to a spacing of 12cm (5in) between plants. Lift the seedlings carefully – the soil should be moist and all thinnings removed to deter onion fly. Closer spacing will give smaller onions than wider spacings. The seedlings can of course be eaten.
Seeds can also be sown into trays 12mm (½in) deep and transplanted outdoors to their growing position by mid October. The roots must fall vertically in the planting hole and the bulb base should be about ½ in (1cm) below the surface. Plant firmly.
If you miss the best sowing time in August, the seeds can also be sown undercover in late January to mid February, this will of course give a later harvest.
If you do have seeds left, you can finish off the packet by sowing in late spring. About three months later you'll get small white bulb onions with a long green top that you can use in salads or cooking.
Hoe carefully or weed by hand – dense weed growth will seriously affect yield. Water if the weather is dry (not otherwise) and feed occasionally. Feed an autumn-sown crop in March and April. Side-dress with a complete organic fertiliser.
Mulching is useful for cutting down the need for water and for suppressing weeds. Break off any flower stems which appear. Stop watering once the onions have swollen and pull back the covering earth or mulch to expose the bulb surface to the sun.
Overwintering onions are best used fresh, they are not intended for long term storing. They are suitable for use as a baby vegetable and can be eaten while still green. Harvest as and when required.
As the bulbs mature the foliage turns yellow and topples over. (Some gardeners bend over the tops as the leaves start to yellow). Leave them to dry in the sun until the tops are brown and dry and carefully lift with a fork on a dry day.
The skin of a white onion will give shades of orange while the skin of the red onion can be used to create a medium green, slightly lighter than forest green.
How to slice an onion without crying:
Freeze the onion for ten minutes before cutting. The sulphuric compound that leads to tears will not react as quickly when it’s cold. If you forget, just light a candle, as a burning flame can burn away the sulphuric fumes.
If you have just painted a room and the fumes are a little overwhelming, slice an onion in half and place it in a bucket of cold water. Leave the bucket in the room overnight. The fumes will magically disappear (or a least be reduced a fair bit).
- Additional Information
Packet Size 2 grams Average Seed Count 500 Seeds Common Name Overwintering, Maincrop, Semi Globe. Other Common Names Japanese Heritage Onion Genus Allium Species cepa Cultivar Senshyu Yellow Synonym Overwintering Onion Hardiness Hardy Biennial Height 45cm (18in) Spread 15cm (6in) Position Choose an open, sunny site with good drainage Time to Sow Sow in Autumn Germination 21 days Time to Harvest Autumn-sown - 46 weeks Notes Stored seed viability: 1-2 years.