The olive tree: advice for its cultivation and maintenance

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The olive tree (Olea europaea L.) is a sturdy, typically Mediterranean tree that has been cultivated since Antiquity for its fruit and olive oil. The olive tree is a mythical tree loaded with symbols: strength, immortality and wealth in the time of ancient Greece, peace in the Bible, source of divine light in the Koran… Olive oil was used in the past not only for food, but also for lighting, some medical care or religious practices, from the 4th century BC. Although it is difficult to accurately date the age of an olive tree, because of its hardwood and irregular growth, history tells us of its exceptional longevity. In Roquebrune-Cap-Martin, in the Alpes-Maritimes, the village olive tree, around 2000 years old, is perhaps the oldest tree in France.

Botanical description of the olive tree

The olive tree, Olea europaea, belongs to the family of oleaceae, around 900 species, which include, among others, lilacs, privet, ash… The leaves of the olive tree are opposite and are said to be decussed because two successive pairs on the stem intersect at right angles. The blade is lanceolate (12 mm x 80 mm approximately), leathery, dark green shiny on the top, silver gray below. The edges are whole and the petiole is short. Only the midrib is clearly visible. The foliage is persistent, the leaves have a lifespan of three years and are constantly renewed. Thanks to their regulating role in the storage of water, they are the essential element of the adaptation of the tree to the arid environment, in hot climates.

The flowers are small and white, formed by a tubular corolla with four rounded petals. Grouped in panicles, the inflorescences appear in the leaf axils, in early spring, on two-year-old twigs. As the flowers are hermaphrodite, the olive tree is naturally self-fertile, that is to say that fertilization is ensured by the pollen of its own flowers. Pollination is anemophilous (pollen carried by the wind), and concerns in the best of cases 10% of flowers, knowing that the tree must reach the age of 15 to 20 years to bear fruit, in the Mediterranean climate. The olive is a drupe (stone fruit), the skin of which is covered with a waterproof waxy material. During ripening, the flesh becomes loaded with lipids. The olive, this oleaginous fruit, remains green during the summer and becomes black at maturity (veraison), that is to say at the beginning of winter. The harvest is staggered from October to the end of winter, according to a number of criteria linked to the destination of the olives (fruit to be put in brine for table consumption or search for an oil, produced in the mill, whose taste qualities are inherent in ripening). The olive harvest is surrounded by a whole know-how: laying a net on the ground, manual or mechanized gapling technique, ventilation (separation of leaves), sorting and grading according to needs.

The different varieties of olive trees

There are two populations of olive trees in the world: wild olive trees, called olive trees and cultivated olive trees. The oleaster, Olea europaea var. sylvestris, is the ancestor of the domestic olive tree, Olea europaea var. europaea. Obtaining the domestic olive tree and selecting it around the world resulted in the census of 2000 cultivars. In France, out of around fifty varieties, we can cite: Aglandau, representing 20% of French olive oil production, Cailletier, variety of AOC olive from Nice, Picholine, variety of the region from Nîmes, used for the production of green olives.

The olive tree, icon of the modern garden

The olive tree has been very appreciated, for several decades, in all regions of France, as a major decorative element of the garden, both for its natural charm and as a Mediterranean symbol, also for the beauty of its silver foliage and especially its old tormented trunks. All this thanks to the know-how of horticulturalists for transplanting trees, even very old ones, in tubs or in the ground. In this case, olive production has become very incidental. A sunny place, sheltered from strong winds, in well-drained land, is ideal for successful planting in the open ground. Knowing that the roots rarely extend above the foliage, you can even plant the olive tree by the pool. Also remember that planting requires a very wide and deep hole, in line with the size of the root ball. Wetland involves drainage or at least a bed of successive layers of large stones, gravel, or even sand. Do not forget that some varieties are frost-resistant from -15 ° C. Even if the subject's age increases their resistance to cold, protection against exceptional frosts should be considered with winter sails. In some regions, cultivation can only be done in containers, which will be brought in the winter in a bright room. Also remember that in the tub, the roots are less protected from the cold. The olive tree requires little maintenance. It resists drought in summer well, however, do not forget the water requirements of the first years of planting. The application of fertilizers is rarely necessary. Horse manure on the surface can be considered. Size is important, especially to fight against certain cryptogamic diseases such as sooty mold or root rot (Armillaria mellea) or other parasites (olive fly, mealybugs, etc.). It takes place at the end of winter. It consists first of all in removing shoots from the foot, then in clearing the antlers or shortening it by remembering the provencal saying, "the little bird must cross it without brushing against its wings". It goes without saying that the pleasure of the olive tree in its garden - representing a certain investment for old trees in particular - can be accompanied, if necessary, by the advice of a professional.