The onion is perhaps the most cultivated vegetable plant in Italy, both for its organoleptic qualities, and for the high content of salts and vitamins present in it. It is assumed that the origin of this vegetable is western Asia.
There are many varieties of this species that can take both different forms and colors. For example, the winter onion (Allium fistulosum), in addition to having a different breeding methodology than the traditional one, also changes in appearance, not presenting the characteristic swelling of the stem.
It is a biennial herbaceous plant with a collated root system that can reach up to a meter and a half in height. Allium cepa is made up of many scales rich in reserve substances. Outside it is covered with a very thin membrane. The leaves are tapered and very pointed and cylindrical. The inflorescence is very showy, pink or white. The shape of the flower is an umbrella and is divided into 3 4 main parts.
The varieties differ from each other both for the final use (fresh consumption, storage, industrial production for pickles), and for the external appearance. One of the most important differences is the harvest time (in fact, spring and summer winter onions are distinguished).
Spring-summer onions are generally white and should be eaten fresh (after harvesting). They are sown in summer, transplanted in autumn and harvested the following spring. On the market there are bulbs that avoid the passage of sowing and are immediately ready for transplanting and cultivation.
Autumn winter onions are to be sown on the ground from the beginning of February to the end of March, while if sown under tunnels, sowing can be anticipated by a couple of months. In the latter case, the picking will take place in early spring and harvested in the summer months. If sowing takes place later, the harvest will continue throughout the autumn period.
As far as industrial varieties (pickles) are concerned, they will be sown in the spring and harvested in the summer. These types of onion are generally white and have a smaller size than the onions mentioned above.
Speaking of cultivation onions, three fundamental factors must be considered to have a good harvest.
1) The soil must be very light, so that the bulb develops homogeneously and without finding resistance from the soil itself in the growth phase.
2) Cultivation temperatures must be tempered. This vegetable in fact suffers when the temperature reaches 0.
3) The contribution of organic substance is fundamental since the Allium cepa needs large amounts of potassium and phosphorus.
For a good preparation of the soil it will be necessary to carry out a deep digging adding organic matter (very mature manure is fine) at a rate of 25 30 kg per 10 square meters. Prepare a well leveled seed bed with the help of a rake. To sow to broadcaster making sure to leave the seed quite sparse. Irrigate abundantly after sowing. When the plants have reached 10-12 cm proceed to thinning (the optimal distance is 14 -16 cm on the row and 25-35 cm between the rows).
Harvesting is based on the type sown. In principle, summer onions are harvested when the leaves turn yellow. Once collected, the onions must be placed to dry in a well-ventilated place, thus avoiding the onset of diseases and rot. Autumn winter onions can be left in the soil even for a longer period. Once collected they must be stored in dark and well-ventilated areas.
Onion cultivation - Allium cepa: Diseases and pests
The diseases that most affect the onions are cryptogamic, even if there are insects that can cause the loss of the crop. The parasites that most frequently affect the onion are the onion moth and the onion fly, whose larvae dig tunnels inside the bulb causing the onset of rot. Against these pests it is advisable to treat the soil with disinfectants beforehand. If, however, the attack occurs when the crop is already in place, the use of systemic insecticides with very short days of deficiency is advised.
As far as fungal diseases are concerned, it is very important to prevent the occurrence of the conditions in which the pathogen succeeds in affecting the natural defenses of the plant. The frequency and time of irrigation is very important in this regard. The best time for watering is in the early hours of the day, when the temperature is low and the ground has a way of drying before the night arrives. The mushrooms that most affect the Allium cepa are the onion blight, which manifests itself with the appearance on the leaves of whitish or greenish spots and the mold of the onions, in which the tips of the leaves turn yellow and the bulb is covered with a whitish mold . Against these diseases you can intervene with products based on ziram and sulfur.