The onion (Allium cepa) is one of those condiment plants that are essential in our cuisine and in that of the whole world, and it is also a vegetable. It originated in Iran and more widely in Central Asia. Before the arrival of the potato, the onion was the basis of the peasants’ diet. It takes its name from the Latin unio meaning “one” in reference to its single indivisible bulb.
Biennial, the onion is generally cultivated in annual, it forms cylindrical tubular leaves, swollen, in the middle of which a hollow floral stem which can reach 1 m in height ends in a white to green flower of spherical form, in big umbel.
What we eat of the onion is its hidden part: the bulb, elongated, flattened or round according to the varieties which are divided between the white onions which are part of the early harvest before maturation, in spring, the yellow onions wrapped with tunics, layers of very thick skin allowing to pass the winter well wrapped and the red onions with the sweet savour but of less good conservation.
The young shoots (green stems) of the onion can replace chives in salads.
Rich in vitamins A, B1, B2, B5, C, E, PP, onions also contain interesting trace elements such as bromine, barium, selenium, sulfur, zinc. Recognized as anti-infectious, antiscorbutic, bactericidal for centuries, the onion also offers digestive, diuretic and stimulating properties. It can be consumed by diabetics since it lowers the blood sugar level. It is also beneficial for the liver and the pancreas.
The onion contains sulphur compounds including alkyl sulphide which becomes volatile as soon as the cells are attacked with a knife during peeling for example: at that moment, it stings your eyes and makes you cry.
- Family: Liliaceae
- Type : aromatic biennial
- Origin : Central Asia
- Color : white to green flowers
- Sowing : yes
- Cutting : no
- Planting : February to April
- Harvest : June-July and August-September
- Height : up to 1 m
Ideal soil and exposure for growing onions in the vegetable garden
A loose, rich and well drained soil is necessary for the onion which likes the sun, under a temperate climate, rather mild.
Sowing and planting onions
Onions can be sown from seed or planted using bulblets. In all cases, the rows should be spaced 25-30 cm apart.
A distinction is made between winter onions intended for conservation, which are sown in February-March, and summer onions, which are sown in August-September and harvested early the following spring. They should be thinned to 15cm.
Bulbs are planted in February-March, every 10cm.
See the file : Planting onions : when and how ?
Advice for the maintenance and cultivation of onions
Onions must be hoeed very regularly until the bulbs are well formed, taking care not to damage them.
They can withstand dry spells. Water only in case of prolonged dryness, especially when the bulbs are growing.
Harvesting, storage and use of onions
Onions are ready to be harvested when their foliage starts to turn slightly yellow, from April to June for summer onions and from August to September for winter onions. They should then be pulled out and left to dry in the sun for 2 to 3 days.
They should be stored in a cool, dry, well-ventilated place, away from humidity and light, spread out on shelves or woven into hanging mats.
The onion can be eaten raw in a sandwich, to accompany a salad, raw vegetables, a marinade or candied in vinegar but it is especially prepared cooked in cooked dishes, sausages, sauces, soups, pies, etc.. It can also be fried.
Diseases, pests and parasites of onions
Damping off, mildew, botrytis, onion fly (Delia antiqua) are the main pests known by the onion, especially in case of too much humidity.
Location and favorable association of the onion with other vegetables in the garden
Onions can be grown next to parsnips, carrots, tomatoes, cucumbers, lettuce, beets, strawberries, but keep them away from legumes (beans, peas…) and potatoes.
Species and varieties of Allium recommended for planting in the garden
The Allium genus includes about 700 species, some of which are used for culinary purposes, such as leeks (Allium porrum), garlic (Allium sativum), shallots (Allium cepa var. ascalonicum) or chives (Allium schoenoprasum), but other species of the Allium genus are purely ornamental, such as ornamental garlic (Allium spp.).
The Allium cepa species includes many varieties that differ in shape, size, color, more or less pungent flavor and storage potential:
green onion: Premier, Prompto, are white onions harvested early ;
white onion: Blanc de Paris, large round bulb, a little flat early, Blanc gros de Rebouillon, large round bulbs, Blanc très hâtif de la reine, ideal for candying, de Vaugirard, rustic…
classic yellow onion: Jaune paille des vertus, a tasty old variety, Jaune de Mulhouse, flat, Jaune de Lescure, adapted to the south-west, Jaune de Moissac, Jaune rond hâtif de Valence, oignon de saint-André or oignon doux des Cévennes, with a mild, sweet taste, without bitterness, it has a PDO (Protected Designation of Origin)…
Red onion : Red of Brunswick, sweet and long, Pale red of Niort, big flat copper bulb, Long red of Florence, with a very fine taste, Piroska red, round and very red…
pink onion: from Roscoff, with a sweet and fragrant taste, it has a PDO (Protected Designation of Origin), and is produced in Finistère, Cuisse de poulet du Poitou or echalion with a long shape…
shallot : most of them are Allium cepa varieties with only vegetative reproduction (bulb which will give other bulbs) !
There is also the rocambole onion (Allium cepa var. proliferatum) called catawissa onion, which is a perpetual onion, or the potato onion (Allium cepa var. aggregatum) the size of a shallot, which multiplies only by vegetative way.