Scientific name: Allium cepa L.
Family: Liliaceae
Brief history and botanical notes on the plant
The onion (Allium cepa L.) is a bulbous cultivated plant, it belongs to the Liliaceae family or rather, some more current taxonomic schemes place it, due to the shape of the inflorescence, in the Amaryllidaceae family like garlic.
Probably native to the highlands of Turkestan and Afghanistan (Western Asia). Its cultivation is very ancient and dates back to the Egyptians, today it is cultivated all over the world. In Italy the regions most interested in this crop are Emilia-Romagna, Campania, Sicily and Puglia; however it is grown practically everywhere, at least at the family garden level. World production is around 40 million tonnes, half of which is produced in China; in second place, far behind in the producer ranking, is India, with around 5.5 million tonnes. In Europe, Spain is the leading producer with 1.2 million tonnes, tenth in the world ranking, while Italy follows far behind with just 300,000 tonnes per year.
The onion is a biennial herbaceous plant, equipped with a root system made up of numerous fasciculated roots which are distributed in the first 25 cm of soil and are white, without root hairs but fleshy. When it germinates, it emits a small, fleshy ring-shaped leaf, which as it grows becomes straight as an arrow and points upwards. The other leaves emerge subsequently and are thick and swollen in the lower part, almost cylindrical in shape, while in the upper part they become thinner and tapered. The plant has many varieties and many different habits and sizes, up to a meter and a half in height.
The thickening of the basal part of the leaves, which become fleshy, colored purple or red, leads to the formation of the bulb, which is the edible part of the plant. On the outside the bulb is covered by a very thin membrane and on the inside it is rich in reserve substances. In the second year of life, the hollow floral scape emerges from the bulb, with the characteristic umbrella shape made up of 3-4 main parts and many flowers. The flowers are protandrous, that is, the male part, the anthers, matures first, then the ovules; fertilization is allogamous, favored by pollinating insects. From the fertilization of each flower a capsule is formed which contains 1-2 seeds, dark and very light: the weight of 1000 seeds is 3-5 grams. Other commonly used varieties are:
red onion from Acquaviva delle Fonti
Suasa onion
red onion from Certaldo
coppery Montoro onion
Borettana onion, sweet, for pickles
Brunate onion: small, white, excellent for preparing pickles (Lake Como area).
Cannara onion
sweet onion
Banari onion
Finally, there are local Piedmontese varieties, less known but of excellent quality, which in turn include other varieties: Asti blonde onion, Asti red onion, golden onion from Castelnuovo Scrivia, Andezeno onion, small onions from Ivrea. These local varieties in turn differ not only in origin, but also in shape, color and final use.
Agronomic needs
The onion is resistant to low temperatures, germinates in optimal conditions around 20-25°C, but germination can already begin at values of 0-1°C. As we said, it is a biennial plant, so it is exposure to low temperatures (vernalization) that allows it to flower. It also has different needs regarding light, the formation of the bulb depends on the photoperiod (day-night alternation):
short-day: require a period of 10-12 hours of light per day (early varieties);
neutrodiurne: require a period of 12-14 hours of light per day (medium-early varieties)
long-diurnal: require a period of 14-16 hours of light per day (late or very late varieties).
It prefers medium-textured, loose soils, to ensure that the bulb develops homogeneously and without finding resistance from the soil itself in the growth phase, but it also adapts to clayey ones as long as they are fresh, deep, rich in organic substance, with values with a pH between 6 and 7 and with good water availability.
Soil preparation and fertilization
The preparation of the soil is a very important operation for the onion, to avoid water stagnation with consequent development of rotting of the bulbs, particularly in clayey soils in which poor water drainage favors attacks by Fusarium spp.
In open fields, plowing at a depth of 30 cm is advisable, perhaps combined with subsoiling, with burial of crop residues which will improve the characteristics of the soil and increase the organic substance content of which the onion is quite demanding.
If you proceed with sowing, it will be important to roll and level the soil, refine it, while if you proceed with planting bulbs or transplanting seedlings, there may also be a certain clodiness.
In small vegetable gardens and for domestic crops, to prepare the soil well, deep digging must be carried out and a well-levelled seedbed must be prepared with the help of a rake. It can be broadcast sown, leaving the seed quite sparse and watered abundantly after sowing. When the plants have reached 10-12 cm proceed with thinning (the optimal distance is 14 -16 cm on the row and 25-35 cm between the rows.
As regards fertilization, it is better not to exceed the supply of organic substance so as not to encourage pathogenic fungi and nematodes in the soil, remembering that the onion benefits from the organic contributions of the previous crop (it is a renewal crop). When preparing the soil, with ploughing, but also in small vegetable gardens where work is done with a spade, mature manure can be added, approximately 200 q per hectare (20 kg every 10 square metres), always in pre-sowing. In organic cultivation the soil must be equipped with a sufficient quantity of organic substance, so there is no need to add nitrogen, also to avoid compromising the quality and shelf life of the product.
The onion is quite demanding in terms of phosphorus and potassium, especially in the 20 days before harvesting, so it may be useful to add wood ash or rock dust to the pile.
Turnover
The onion suffers greatly from soil fatigue, so it is considered a renewal crop that opens up the rotation. A rotation at least every three years is advisable, but a long rotation is better (every 4-5 years), following it with cereals, grassland crops, carrot, radicchio or salad and avoiding following it with cabbage, potato or sugar beet as characterized by phytosanitary problems similar to those of the onion. If problems with fungal diseases or nematodes have occurred, it is better to rotate for 7-8 years before growing the onion on the same soil again.
Cultivation techniques: Sowing, transplanting and bulbs, Irrigation
The onion planting methods can be: direct sowing, transplanting seedlings, planting bulbs. On large surfaces, and for industrial onions (given the high planting density), direct sowing is preferred, while for small areas and family gardens, transplanting or planting bulbs is preferred.
The planting time depends on the intended use of the product:
onions for fresh consumption: sowing takes place from mid-August to mid-September or in February; the transplant is instead carried out from September to December.
Serbian onions: sown from January to April with summer-autumn harvest,
spring onions: sown directly in the field from February to April.
family gardens: the most frequent production is bulbs to be swollen, so planting takes place from late winter to early spring.
Sowing can be done with seed drills or by hand (for small areas), or on pre-seeded biodegradable sheets in contact with the ground. This system allows for seed savings and a reduction in subsequent thinning operations.
The final destination of the product must be considered, so for large bulb onions the rows must be about 20 cm apart, while for small bulb onions 10 cm is sufficient; 5 – 10 cm is enough for pickled onions (even broadcast). The distance on the row goes from 2–3 cm for spring onions to 15 cm for onions with larger bulbs. The seed should be placed at a depth of 2-3 cm, better by rolling the soil so that it adheres well to the seed. The quantity of seed used is 2-4 g square metre.
After 40 – 80 days from sowing in the seedbed, seedlings of 3-5 leaves are obtained ready to be transplanted (by hand for small surfaces or by machine) and buried at 4-5 cm.
If you choose to plant the bulbs, used for planting onions to be consumed fresh, the cultivation cycle is shortened by approximately 20 days. They are buried at the beginning of autumn in rows 35 –40 cm apart and about 15 cm apart on the rows.
The onion is very sensitive to water stagnation, but equally sensitive to water stress due to the small root system, so it would be advisable to do micro-irrigation to save water or in any case frequent but limited irrigation to maintain an adequate level of humidity in the soil. without causing root rot. Generally, water supplies are suspended 25 – 30 days before harvesting or when 20 – 25% of the foliage has settled spontaneously on the ground. In fact, further contributions could damage the shelf life of the bulbs.
Weeds, diseases and adversities
The onion is sensitive to climatic trends and the agronomic techniques to which it is subjected. When a normal climate trend is followed by temperature drops to 10-12°C and a subsequent sudden rise in temperature, pre-flowering can occur, whereby the plant goes to flower without forming the bulb.
Suffering a lot from water stagnation, various types of rot and mycosis can be frequent on both the aerial and underground parts. As regards fungal diseases, downy mildew and onion mold are the most frequent, the former causes whitish or greenish spots on the leaves, the latter causes yellowing of the leaf tip and white mold on the bulb. Careful and precise distributions of sulfur and copper will solve the problem, but you can also resort to distributing lithotamnium powder on the seedlings.
The parasites that most frequently affect onions are the onion moth and the onion fly, whose larvae dig tunnels inside the bulb, also causing the onset of rot; in these cases it will be useful to treat with potassium salts of fatty acids (even Marseille soap diluted 20g/litre is fine), with pyrethrum or organic products based on azadirachtin.
However, the correct management of water and soil will allow us to prevent the conditions in which the pathogen manages to undermine the natural defenses of the plant and to make the environment as healthy as possible for our onions, and therefore to limit interventions of defense. A healthy and lively soil will make the plant healthy and therefore able to defend itself from the attack of pathogens or parasites or in any case able to limit the damage.
Irrigation management is fundamental: the best time for watering is in the early hours of the morning, when the temperature is low and the soil has the opportunity to dry before the night arrives without causing stagnation and consequent excess humidity, both for hypogeal and epigeal part of the onion.
Equal attention must be paid to creating a certain balance in our garden, so that the natural antagonists of parasites can grow. For nematodes and related physiopathologies, it will be essential to respect the rotation times to avoid becoming tired of the soil.
A separate chapter is that of weeds. The fight will obviously be based on mechanical means, such as weeding, false sowing before planting and precision pyro-weeding.
Collection and conservation
The onion is harvested from March-April, in the case of the earliest varieties, to June-July for all the later fresh varieties; the harvest of winter varieties, however, takes place from August to September. It depends on the variety and the climate, but in general the onion is ready to be harvested around 90-120 days after sowing, when the leaves appear wilted, yellowed and curved towards the ground due to the loss of turgidity. In large areas it is usually carried out with excavator-aligning machines which dislodge the bulbs from the windrows, leaving them in the field for a week to complete the drying of the roots and the aerial part; subsequently, the harvest is carried out with the harvester.
In small or family-run gardens, it is important to dry the freshly harvested onions in a dark and well-ventilated place, thus avoiding the onset of diseases and rot. If you want to make braids, you will have to pick them when the leaves are not well dried and let them dry with the braid formed. For optimal conservation it would be best to store them at around 10°C, with a relative humidity of 50%.
The harvested bulbs, depending on the variety, can be used immediately for fresh consumption and for the processing industry for the production of pickles, pickles or dehydrated slices or can be preserved (late ones are better).
Use, chemical and nutritional properties, curiosities
Onion is one of the most used foods at all latitudes of the globe, both for preparing soups, meats, sauces, salads, etc. as an aroma, both as a side dish and as an aperitif. Its particular taste gives the preparations that flavor that enhances the other ingredients used in the various dishes of national and international cuisine. Gastronomy and variety have evolved together, one pushing the other to create countless types of onion, different in shape, size, taste and intensity of aroma, color of the skin and pulp, speed of cooking, shelf life , harvest time and intended use. You could say, “to each his own onion”!!!
Its nutritional value is linked above all to the presence of mineral salts, vitamins, especially vitamin C, chromium and many sulfur oxides, which are the cause of tearing and the strong onion smell when we cut it. By cutting the onion, we break the cellular vacuoles and allow contact between the allinase enzyme (found in the vacuole) and cytoplasmic precursors called alkenyl cysteine sulfoxides; this contact allows the chemical reaction that leads to the release of ammonia, sulfenic acids and pyruvate. Sulfenic acid, attacked by another lacrimal factor enzyme (correct name Lacrimathory Factor Shyntase), forms a volatile molecule which, in contact with the liquid of the eyeball, transforms into sulfuric acid, generating the lachrymogenic effect. The tears combine with other volatile molecules, generating more sulfuric acid in a chain reaction!!!! Obviously the concentration of the acid is very low and the effect is absolutely not harmful!
Historically, the onion has always had an important place in the human diet and also in traditional medicine.
In archaeological excavations, remains of onions have been found in Bronze Age settlements from around 7000 years ago, but it is probably only in the Egyptian civilization that the cultivation of onions began, along with garlic, leeks and radishes.
For the Egyptians it was sacred because its shape and concentric rings are a reminder of eternal life, the cycle of life. It seems that the diet of the workers who built the pyramids included a considerable amount of garlic and onion and two onions were found in the eye sockets of the mummy of Ramesses II! It's curious to see how tastes change over time: for us the strong smell of onion can be heavy, annoying, but the Egyptians believed that the strong aroma of onion could bring life and breath back to the dead!!!!
Following the path of the onion in history, in ancient Greece athletes ate large quantities of it because it was believed to promote circulation and have an anticoagulant effect; Roman gladiators smeared onion poultices on their muscles to firm them; in the Middle Ages onions were used to pay rent or as a prized gift because they were an important source of nutrition and as a cure for snake bites, hair loss and sterility.
In 1493 Christopher Columbus brought onions to America for the first time and since then they have had an incredible spread on the continent, where today there is no fast food that does not include "onion rings" on the menu, fried in batter !!
Even today, properties that can be defined as therapeutic are recognized: it has an antibacterial and anti-infective action, a diuretic, promoting the elimination of nitrogenous waste, against intestinal worms, it contains blood sugar, cholesterol and triglycerides, preventing heart disease, it contains many flavonoids including quercitin which has an anti-carcinogenic effect.
A very important action, which we can all experience, is the anti-inflammatory one, both general on the organism, but in particular for topical use: onion poultices, due to the sulfur and ammonia content, have an immediate anti-inflammatory effect on dog bites. hymenopteran insects and jellyfish. In the case of contact with a jellyfish, even just passing an onion cut in half over the wound provides immediate relief and, moreover, a scar will not form.
Onion cultivation and biodynamics
The onion is a plant with two dynamic poles because it is both a bulb and a flower, depending on the cycle we make it go through, whether we want it to go to seed or whether we want to harvest the bulb.
In the second case it will be treated as a land plant (from root), therefore it will be advisable to follow the biodynamic calendar and carry out the operations (sowing, harvesting, weeding, etc.) on earth days and descending moon days.
Since care of the soil and good agronomic practices are essential to obtain a quality product and prevent pathologies, it will be advisable to treat the soil with the preparation 500 before the main processing and spray the 501 when the plant has produced at least 2 or 3 leaves, in the morning on sunny, clear days, and renew the treatment two more times on root days. Using 501 for the best quality will be very useful if we have clayey soil and is subject to water stagnation.