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Olive tree multiplication and methods of plants production
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 On the one hand olive tree multiplication can be easy to achieve if traditional methods of propagation are used (woody cuttings, root cuttings separation, grafting etc.) ; On the other hand, it can be delicate and require certain skills if the aim is to intensify the production of plants (as in nurseries where semi-grafting and propagation by semi-woody cuttings are done).
Traditional methods of propagation are mainly used in those arid cultivation areas where olive trees are transplanted and irrigation is minimal. Often, these olive growing areas are marginal ; there, the olive tree is intensely cultivated, mainly for the local population’s own consumption.
However, olive trees that are intensely multiplied in nurseries are intended for modern-type and high-density  plantations where their products- oil or table oil- supply local markets as well as export markets

These young olive trees have to comply with some standard requirements :

  • The variety must satisfy the production targets as planned by development forecasts and the market’s requirements.
  • The phytosanitary quality of the trees towards tuberculosis (pseudomonas savastanoï) ;
  • The homogeneity of the trees produced in nurseries to ensure homogenuous productions in olive groves.
  • And lastly but mostly, the intensive production of young olive trees in order to meet national olive-growing programmes’s development targets.
plantation d'olivier dans le midi Traditional multiplication methods.
Traditional propagation is first of all asexual (vegetative), as opposed to sexual propagation (seed) for which grafting is used.
Different methods are frequently used in different countries and areas according to environmental conditions (soil and climate). Most methods involve propagation by cuttings since the olive tree’s woody tissue is able to give out new roots, a.k.a neoformation roots, easily. In addition, the scars thus created heal very easily.
oliviers et midi de la france Propagation by cuttings from woody branches. This method of propagation is still used in nurseries in order to produce young trees from stocks that have been selected for their quality of yield and their sanitary condition. Unfortunately, this type of propagation requires a high amount of wood, which is very hard to find on pruned wood from orchards that have been picked out for their yield and good sanitary condition. Various plant material is used in the production of cuttings according to the planting techniques used in nurseries

bouturage d'oliviers
  • Vertical cuttings :
    The cuttings are planted vertically in the loosened soil of the nursery in February/March.

systeme de bouturage
  • Horizontal cuttings :
    The cuttings are planted horizontally at the same time of year, in February/March. Several sprouts may develop and give out roots along the cutting, thus creating several young trees.For both horizontal and vertical cuttings, the trees have to stay at least a year in the nursery before being transplanted. In arid areas, cuttings should be cultivated for 2 years in nurseries.

technique de bouturage
  • « Garrote » cuttings :
    Woody cuttings ; Length from 0.60 to 1 m, diameter from 4 to 5 cm

bouturage
  • Estacas plantones cuttings:
    Woody cuttings that can be up to 2 m long, with a diameter from 6 to 9 cm.


 « Garrotte » and estacas plantones cuttings :
These techniques of propagation are still used by some olive-growers in Spain (Andalusia).
In an olive orchard, the aim is to replace older, non-yielding olive trees through propagation by large cuttings. The latter are formed of olive branches of 1 to 2m long and 5 to 6cm in diameter. They can better withstand adverse climatic conditions, lack of care, cattle’s bites and so on…


« Garrotes » are woody cuttings from 0.6 to 1 m long with a diameter from 4 to 5 cm. They are laid in the same  hole gy groups of three or four with their tops showing.

They will then form a group of trees with 3 or 4 distinct trunks. The usage of the word Garrotte has been widely generalized. It was originally used to refer to the planting out of three or four young rooted olive trees in the same hole.

Estacas plantones are even bigger cuttings. They can be more than 2m long with  a diameter generally over 6cm. These large cuttings are laid individually and vertically in the hole with only one-third of their length buried. The external part of the cutting is protected by a cone of soil. Only  0.20 to 0.30m of the top part is showing. It is this part that will give out the first offshoots.


Truncheon cuttings:

Olive tree propagation by truncheon (or root cutting or ovuli) is used in arid and sub-arid areas (Southern Tunisia, Lybia…). This technique is used on seedling plants’ roots, as for the  CHEMLALI-SFAX variety. It consists in cutting off pieces of the excrescences that develop around the collar of older trees. The tree on which the pieces are collected may then either be completely uprooted or stay in place if only parts of its excrescences have been  removed.


The very first excrescences, that grow  around the collar, are very smooth. They are cut in pieces about 15 to 20cm long which can weigh from 500g to 5 or 6kg. On the whole, one may collect 2 to 5 truncheon cuttings per seedling plant without significantly jeopardizing its vitality.

Suckering and clump layering:
These propagation techniques are rarely used, except in some particular cases, as when replacing older orchard trees.  The suckering technique consists in collecting sprouts from their roots and planting them directly in the orchard.  Sometimes, it is possible for the sucker to grow next to the mother plant without being cut off. When it has sufficiently grown, it then replaces the mother plant which is gradually eliminated.

 Clump layering consists in re-ridging the young sprouts of the mother plant  so as to facilitate the growth of young roots. Once the layers have been separated from the mother plant, the rooted offshoots are planted in the orchard. Offshoots of a small diameter are relatively drought-sensitive.


In both techniques if the sprouts come from grafted trees, i.e from rootstocks, they have to be grafted with the variety to be propagated.


General principles about pruning :
The practice of pruning by cutting off branches produces more or less important changes on the plant depending on its « intensity ». These physiological changes have in turn an effect on the tree’s biology.


Indeed, an olive tree that has not been pruned will  turn into a bushy tree with several trunks originating from the growth of several sprouts at its base.


If only one sprout is kept, the tree will grow from a more or less big trunk, leafing will take place higher in the plant and a tree will grow. Fructification will tend to take place at the branches’ ends on the previous year’s wood whereas older branches at the base will tend to thin out.

The  surface area of the olive tree’s evergreen leaves plays a major role there. Indeed, evergreen leaves take in a lot more of carbohydrates than deciduous leaves. By eliminating « active » branches, heavy pruning may upset the tree’s natural metabolism.
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