(Genus: Allium cepa - Family: Amaryllidaceae)
The Onion and its origins
A native of Central and Western Asia, onions have been used as a food for thousands of years and it is believed that the plant pre-dates the Bronze Age, although it was not cultivated until much later. Evidence of the onion’s existence has been found in early Bronze Age settlements including Liliaceae Canaanites (XV-XIII century BC). It is not known whether these onions were cultivated.
How to Plant: Onion
Onions thrive in a warm, temperate climate with optimum temperatures of 15-23°C. It is a hardy plant that can adapt to the cold, if necessary.
The timing for sowing seeds varies depending on the final destination of the onion, for e.g. an onion that will be pickled will have different timings to one for fresh consumption.
Growing onion from seed can be difficult for a novice gardener. It is often easier and more common to grow from an onion set. Onion sets are essentially immature onions that have been grown from seed by an expert. They can be planted directly between February and March. Plant the sets in rows with a distance of 15-20cm between a set and 30cm between each row, at a depth of 0.5-1cm.
If planting from seed, Onions should be sown in a seed bed from February to March and then transplanted from March to April. Seed can also be set in the months of September to November and then transplanted from October-December, depending on the climate.
Seedlings are ready for transplanting when they have developed 4-5 leaves. For autumn sown seedlings, plant them a little deeper, covering in soil up to the neck, protecting the roots in colder conditions. Spring seedlings can be laid in small furrows and require less protection.
Soil should be very light, loose and free from stagnant water; onions prefer soil with a slightly acidic pH. The onion is very demanding when it comes to fertiliser, especially potassium and phosphorus based fertilisers.
Pre-sowing, soil preparation is done with xxxxxxxxxxxxxxxx xxx (xx g/m²). Two further follow-up doses are required using the same fertiliser at a rate of xxg/m²; the first of these doses taking place when 2-3 leaves have appeared on the plant and the final dose when the bulb has become enlarged. Alternatively, when foliage first appears, use xx-xx g/m2 of xxxx xxxx, immediate-release fertiliser. Avoid using manure which can rot the bulb.
Water onions regularly but in moderation, as the plant is sensitive to either over-watered or dry soil.
When to harvest onions
Onions traditionally come in three colours yellow, red and white. The onion plant is comprises flowers, roots, leaves and a bulb, this being the key edible section. Grown as an annual, they have a 2 year cycle. The flowers are yellowish- white colour but can also be pink and form an umbrella shaped bloom.
The onion bulb is composed of several layers rich layers of flesh and a thin membrane outer cover.
The plant is harvested from summer to early autumn. Once the foliage begins to die-back and turn a yellow-brown colour, the plant is ready for harvesting.
To store onions over the winter, place the bulbs with leaves attached in direct sunlight and allow dry-out. Then place the onions in an airing cupboard or similar warm, dry place for 10-15 days. Finally, hang them in a dry place at a temperature of 3-4oC.
Did you know
Over the centuries, onions have always been in great demand, not only as a source of food but also for their perceived medicinal value and importance. Packed full of vitamins A, B1, B2 and C, it also contains minerals. It fights infection and stimulates kidney function by promoting the elimination of nitrogenous waste. Different cultures have used the onion for everything from treating bee stings to sore throats.
It is used in all types of cooking and can be eaten raw, pickled, fried, caramelised or dried and ground into onion powder that is used as a seasoning.
Watering eyes are a common side effect experienced when chopping raw onion. Sulphenic acid is an aromatic compound present in onions that creates the characteristic odour; it is also the cause of watery eyes. When cut, cells are broken down that contain an enzyme which is abundantly released called allinase. It produces sulphenic acids and propylene oxide, a volatile gas which turns into sulphuric acid in low levels and makes contact with the aqueous humour on the eyeball. The tear gland produces tears to flush out and protect the eyeball.
The secret to prevent crying when chopping...cut onions in running water to stop the gas reaching the eye.