Fruit and Vegetables

Onion - Allium cepa

Onion - Allium cepa

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Onions, Allium cepa, are one of the most cultivated species of allium, along with garlic, Allium sativum, and leek, Allium porrum; they are biennial herbaceous plants, cultivated as annuals, which produce an enlarged bulb, and a head the elongated leaves; at the center of the stem, in summer, a thin, fleshy stem rises, which can exceed one meter in height, at the apex of which a particular spherical inflorescence blooms, consisting of small white tubular flowers, very decorative. The flowers are followed by seeds, and then the plant dries up and dies; flowering occurs the second year after planting, so it is highly unlikely that the onions grown in the family garden, which are harvested as soon as the bulb gets bigger, will eventually produce flowers. The part that is consumed of the onion is the bulb, at the base of the leaves; bulb plants tend to store in these underground organs the nutrients that will be used for flowering the following year; it is therefore essential that the onions do not go to flower, or otherwise the bulb would be wasted, and of little interest for consumption. While many bulb plants store nutrients in the form of starches, giving rise to powdery bulbs and tubers (such as potatoes), onions contain a lot of water and simple sugars, which, when cooked, easily caramelize, giving rise to a dish with a very sweet taste. Onions also contain sulfur-based substances, very volatile, which reach the air around the face at the time of cutting; combining with the water contained in the tears of our eyes, a chemical process takes place which releases minimal amounts of sulfuric acid, a strongly irritating substance; the result is copious tearing, which further feeds the production of the irritant, producing a constant increase in tears. For this reason, by slicing large amounts of onions we continue to tear copiously. Fortunately, the substances that cause irritation are very soluble in water, so it is an excellent trick to peel and cut the onions under running water.

Variety of onions

Onions have been grown by man for many millennia, it seems they were already cultivated during the Bronze Age, they were widespread among the ancient Egyptians, who revered them as a symbol of eternal life; the Greeks used it extensively and since ancient times this vegetable has been constantly cultivated by man; it is therefore difficult to know where the first onion was born and what was its appearance or flavor. Today there are many varieties of onion, all belonging to the Allium cepa species. The differences between the various species depend on the shape of the bulbs, on the color of the external film that covers them, on the internal conformation of the bulbs, or even simply on the precociousness of the harvest.

White onions

Very common, they have a round or oval shape, and the color of the pulp, and of the thin outer papyrus leaves is pure white; the taste of white onions is generally not very aromatic, but sweet; these onions are grown mainly for the canning industry, but are also commonly sold fresh on the market. Very common in northern Italy is the white Chioggia onion, with an almost pearly color; in the central south the most common is the onion bank of Barletta. These varieties of onion are particularly suitable for sowing in summer, for a spring harvest, or in spring, for a late summer harvest.

Flat onions

Also called spring onions, they are in effect white onions; from the early pier development, these onions have a particular, very flattened bulb, generally consisting of a low number of thick and fleshy tunics. This type of onions are among the first fresh vegetables ready between the end of winter and the beginning of spring, and are generally eaten fresh, as they are not suitable for storage, as is usually the case for most onions. white cultivated. The flavor of the cooked pulp is decidedly very sweet, not very aromatic, and contains low amounts of sulfur, which makes them easier to clean; often the outer tunics are completely fleshy, and the papyrus part is usually very thin. Traditionally these onions are cooked whole, in the oven, flavored with oregano and capers, or with basil.

Golden onions

Perhaps among the most sold and spread onions around the world, the golden onions have white flesh, but the external, rigid and consistent tunics, are of gilded bronze color. These onions are sweet and aromatic, and are widely used in the kitchen, although they usually prefer to grow white or red onions in the garden. These onions are usually grown mainly for consumption of dried fruits, that is, with well-dried outer tunics, which protect them for several months; it is difficult to find early golden onions or picked as spring onions. These are the most versatile and common onions. These onions are roundish or elongated oval, and there are varieties of small bulb, but also of giant bulb, which can easily reach 7-8 cm in diameter. Piedmontese varieties are very widespread, such as the golden onion of Castelnuovo Scrivia, but also the different varieties of Lombardy, Pavia, Voghera and other areas of the Po Valley.

Red onion

Red onions are among the most aromatic, often also used raw or simply marinated; the most famous are and Tropea red onions, with a decidedly very sweet and pleasant taste. The outer tunics are bright, purple, and the same is true for the outer side of the various layers that make up the edible pulp; most of the red onions keep their color even after cooking, giving a particular effect to the dishes; some varieties instead, once cooked, have no distinctive appearance compared to other onions, although usually the sweet taste is still marked. The red color is given by the flavonoids contained in the pulp, which makes these onions particularly healthy, especially if eaten raw.


The spring onions, called in the Anglo-Saxon areas spring onions, are nothing but common onions, harvested before the bulb becomes bloated; in this way the layers containing the pulp are particularly thin and crunchy; but even the first part of the leaves is thinner and can be safely eaten, even raw. The onions are cultivated only briefly, and usually the plant has not yet been able to store in the bulb all the substances that we usually find in mature onions; for this reason, often the taste is more delicate, they hardly make us cry when we cut them and we can easily use them even raw, in pinzimonio, without being afraid of being attacked by the strong complex flavor that emanates instead from a very developed onion. Very appreciated in all the kitchens, the onions are typical ingredients of Asian cuisine, both raw and cooked.


It was thought that shallot was a particular species of allium, called allium ascalonicum; in fact, subsequent studies have shown that shallot is a variety of onion, whose botanical name is Allium cepa var. aggregatum; in fact the shallots are onions whose development produces, within each single bulb, several cloves, giving rise to a sort of onion that can be subdivided, as happens with garlic. Despite this similarity, the belief that the shallot is a hybrid of onion and garlic is entirely a legend, as it is instead an onion in all respects. The dimensions are usually smaller than even a small onion, in fact the shallots tend to produce very small, often very elongated, bulbs, consisting of decidedly tiny bulbs, the size of a clove of garlic. There are many varieties of shallots, with usually red or golden tunics, and pulp made up of many very thin layers. The flavor is decidedly very aromatic and quite sweet, and the pungent and sulphurous part of the onion is decidedly much less intense in the shallot.

Grow an onion

Onions are grown in different ways, depending on variety, cultivation area, time of year; typically the varieties to be picked in the early spring period are grown by planting the bulbils taken from the plants of the previous year; the plants that are instead planted in spring, for a summer harvest, are instead often sown, taking the seeds from the plants that were made to flower the summer of the previous year. There are different points of view, regional uses, and visions of the world, which lead to having many variations of cultivation, perhaps as many as the existing varieties of onion.
The cultivation period is very long, and basically it can last all year, with every single variety concluding its development in the space of three or four months; the first onions are usually planted in autumn, starting in September, until the arrival of frost, these onions are usually white varieties, to be picked early in spring, but it is also possible to sow golden onions; at the end of winter or early spring, from January to the first warm, the onions are planted instead which will mature in the summer, which are generally golden or red, and will then be kept for several months. Sowing can also take place early, in sheltered containers, so that small plants already about 7-8 cm high are planted, making it easier to place them in the plots. Whether you choose cloves, seeds or seedlings, onions should always be planted in rows, leaving at least a dozen centimeters of free space between each future plant. If we are sowing, after germination we are going to remove the excess seedlings, or we will harvest them before they ripen, to use them as spring onions. Since we will have to guarantee to a large bulb to widen at best, it is important that the soil is rich and very soft, and also well drained, otherwise, in very firm and compact soils, we risk that the bulb is compressed by the ground, developing little and of bizarre shape. The terreo will be previously worked and enriched with manure. After planting the onions, we will keep the soil fairly wet, watering only if it remains dry for a long time. Cultivation during the cooler months of the year relieves us a little, because the rains will tend to help us. Onion bulbs tend to develop very superficially, and to come out of the ground as they grow, this is why it is important to keep the plot free from weeds, and periodically cover the bulbs that come out of the ground when they are not yet completely enlarged. Shortly before harvest, we can cut the leaves in half over the onions, to prevent the stems already present from starting to develop to prepare for flowering. Typically, however, the harvest takes place before the rest period, and therefore the aerial part should naturally tend to turn yellow and to decay, a sign that the harvest time has come.

Onion - Allium cepa: Pests and diseases

The main animal parasites of the onion are usually nematodes, tiny in size, which ruin the foliage; fortunately the acrid smell that also emanates from the foliage tends to keep away most of the insects, not only from the onions, but often also from the vegetables that we grow around them. The main diseases that concern us in the family garden are various types of fungi, which can develop during the vegetation of the bulb; usually it is rottenness, which tends to develop in case of excessive humidity. Botrytis, in addition to still developing in the field, tends to continue to grow even among the onions that we preserve over the months, and for this reason it is often very useful to let the onions dry in the sun immediately after harvesting them. Other problems for onions can occur in case of incorrect cultivation, or in adverse weather conditions: for example late frosts can cause the freezing of bulbs emerging from the soil, which are therefore inedible; a soil that is not very rich or slightly worked can cause a lack of bulb growth, with plants that produce flowers already during the first months after planting; this type of problem is avoided simply by guaranteeing a good rich and soft soil, and watering regularly, especially in the case of dry periods.
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