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Since ancient times, the olive was considered a symbol of fertility and rebirth, an emblem of peace; just think that there are about seventy quotations in the Bible: for example we remember the olive branch carried in the beak of the dove after the universal flood. The ancient Romans rewarded the most valiant citizens by placing crowns of intertwined olive branches on their heads or necks.
This plant is set very well along all the coasts of the Mediterranean Sea, joining the cultivation of citrus fruits. In Italy the olive groves are widespread in Liguria, Tuscany, throughout the central south and in the islands, with a strong presence also around the lakes of Lombardy and Veneto. The region that holds the primacy of olive cultivation is Puglia, where it calculates that five million trees grow. In recent years this fruit tree has been successfully implanted in other countries with a climate similar to ours, such as California, Australia, Argentina and South Africa. However, the major world producers remain Spain, Italy, Greece and Turkey.
The cultivation of the olive is not particularly laborious, since this tree adapts to the difficult conditions of poor and poorly irrigated soils. It should also be considered that its firm roots allow it to anchor on steep slopes, avoiding their landslides.
General olive characteristics
Olive trees are evergreen trees, therefore with a continuous vegetative phase, which slows down only slightly in winter. They can reach a height between 9 and 12 meters and a leaf width of about 8 meters. The roots are very superficial and can expand even in rocky terrain.
The leaves of the plant have a lanceolate shape and are leathery; the flowers are hermaphroditic and white in color. The fruit, the olive, is an oval-shaped drupe up to four centimeters long; it can be harvested when it is still green or when it is ripe and has a purple-black color. In nature, the only oil extracted from a fruit is olive oil, all other vegetable oils are derived from seeds.
This plant grows in warm and temperate climates, where the temperature remains between five and twenty-five degrees Celsius; in fact, it needs long and hot summers so that its fruits reach full maturity, but together with a good winter cold. It is a very long-lived plant, because it manages to regenerate its damaged parts.
Advise with experts to decide which cultivars to plant in your area: in our country there are about five hundred. If you intend to start oil production, keep in mind that this is strongly influenced by the cultivar. Furthermore, the "typicality" of the oil, and therefore its trademarks of Designation of Origin, is attributed if the criteria that establish the varieties of its territory are respected.
Soil and fertilizer for the olive tree
The plant adapts to almost all soils, but in very fertile ones it may have excessive vegetative growth; important, however, to guarantee a well-drained and not excessively windy site, otherwise windbreak barriers will be necessary. The alkaline soils are the best, with a pH lower than 8.5. They must be planted at least six meters apart from each other.
Prepare the cultivation area in spring, removing all the weeds and weeds; then, move the soil deep and level it. Towards May you begin to create furrows, about one meter and a half wide and one meter deep: this earth will be watered and fertilized during the summer. In September, plant the young plants and cover the roots with soil and fertilizer; within a month you will see the first shoots appear.
Only in the first years of growth it is necessary to fertilize, with a product with a medium-high level of nitrogen: sprinkle about 0.5-1 kg per tree. Even the waterings are indispensable in the first years, subsequently wet only if the season is very dry. Under the olive tree weeds should not grow.
Prune the newly planted olive trees, when they have reached a height of one and a half meters, eliminating the bearing sprout and favoring three or four strong lateral branches. The subsequent prunings will serve to remove the older branches; this will favor the development of new shoots and the production of olives, which come out on the branches of a year.
Olive flowering and fruiting
Olive trees bloom and give fruit after three or four years from their planting; every year they produce a greater number of olives, but by the fifteen years the production stabilizes. A plant can also produce 25 kg of olives in a season. Taking into account the intended use, the olives are harvested at a precise degree of ripeness. If they are put in brine, they are removed from the tree still green and subjected to a treatment to attenuate the bitter taste. Those destined for the production of oil or for food consumption must be perfectly ripe and are harvested at the beginning of the cold season; the harvesting procedure consists in shaking the branches - manually or with a machine - until the olives fall into a net under the plant. Otherwise, the same result can be obtained by "combing" the branches with a rake and then removing what fell to the ground from the leaves and twigs.
Now the olives are ready to be processed at the mill; also in this area it will be cleaned, by aspiration and washing. In the crushing process, the fruits are crushed so that the oil, contained in the small cells contained in the pulp called vacuoles, comes out quickly. The crusher machine works by stirring the dough made from olives, to add the drops of oil into gradually larger drops, thus facilitating extraction.
The oil obtained is left to rest for a few days to eliminate water and air deposits; then it is filtered and racked and is ready to be taken home.
Olive tree diseases
Olive trees can be subject to attack by pests or diseases. Various types of cochineal and the nematode galligenous attack the plants: if the first is resolved with a winter treatment based on mineral oils, for the nematode worm, which penetrates the roots, the intervention of a professional is needed which could also indicate burn the plant. But the cultivation of olive trees is particularly afflicted by the white fly: these are small clear insects that leave their larvae on the leaves, which are covered with a sticky substance. Pesticides generally solve the problem, although in recent years it has been shown that some strains of white fly have developed resistance.