In our case, based on the data we have collected over the last 10 years, the amount of oil produced by an olive tree is around 5 to 10 liters.
So, when you drive through a landscape of olive groves, you can quickly get an idea of how much each tree produces: on average, around one and a half of the typical 5-liter bottles you see in stores.
What does the amount of oil produced by an olive tree depend on?
An olive tree produces more or less oil depending on the following factors:
- the age and size of the tree's crown
- whether the olive tree is rain-fed or irrigated
- the weather conditions during the year
- alternate bearing
- agronomic care, including fertilization, treatments and pruning
Let's take a closer look at each of these factors.
Age and size of the olive tree's crown (for example, in traditional and intensive olive groves)
When an olive tree is planted, it does not begin to produce fruit immediately. Olive seedlings are usually about one meter tall when bought from a garden center, just tall enough to be attached to a stake and fitted with a protective guard to prevent rabbits from gnawing at the trunk.
Obviously, such a young tree does not produce olives. You generally have to wait until the tree is 4 or 5 years old before it begins to produce olives. The farmer will harvest the olives even during these early years, despite the fact that it is not economically worthwhile, because leaving them on the tree would slow down its growth.
During these years, the aim is for the trunk to reach a clear height of at least 1 meter without branches, so that the tree can eventually be harvested using a vibrating clamp. The aim is also to develop three main branches from which the crown of the olive tree will grow.
An olive tree in a traditional or intensive planting system can reach its maximum production level between 15 and 20 years of age, depending on water availability, the absence of disease and severe frost, and the correct and sufficient application of fertilizer.
As for the size of the crown, this is limited by the available space, which depends on the planting density.
In traditional olive groves, with a density of fewer than 200 trees per hectare, the olive trees are more widely spaced and are usually larger. As a result, each tree can produce more oil than a tree in an intensive or super-intensive olive grove.
In these traditional olive groves, the limiting factor was not, and still is not, space, but rather the availability of water, especially in rain-fed conditions.
In intensive olive groves, with densities of between 300 and 400 trees per hectare, the development of the crowns is limited by neighboring olive trees. Consequently, the amount of oil produced per tree is lower than that of a tree in a traditional olive grove.
Another matter to consider is oil production per hectare. In this respect, intensive olive groves usually produce more oil per hectare than traditional olive groves.
Irrigated or rain-fed olive trees
Although olive trees have traditionally been grown as a rain-fed crop and can produce fruit without excessive drought, irrigating an olive grove generally increases the amount of oil that each olive tree can produce.
Traditionally, in order to maximize the effect of irrigation on the harvest, the aim has been to use irrigation to compensate for a lack of spring and autumn rainfall in dry years, and to extend the growing season in years when rainfall is otherwise sufficient. In other words, irrigation can extend the spring period into May and June.
Extending the rainy season in autumn would have little effect and could even be counterproductive, as this coincides with the harvest period. In October, the veraison of the olive begins, when the fruit changes color from green to purple. Once this process begins, the production of oil inside the olive (lipogenesis) comes to an end. Any additional water supplied to the olive tree therefore mainly increases the water content of the fruit, which can make oil extraction at the mill more difficult.
Weather conditions
Weather conditions can have a significant effect on olive production. In addition to water availability, whether from irrigation or rainfall, the main factors are the following:
- The absence of severe frost in winter, and especially of late spring frosts. These are particularly damaging to production because the new shoots responsible for future harvests have already developed and can be easily damaged by a late frost.
- The temperature during flowering. Olive trees flower in mid-May. Excessively high temperatures can cause the flowers to wither, significantly reducing the number of olives that will eventually develop.
Alternate bearing
Alternate bearing is a very common phenomenon in olive cultivation. The Spanish term "vecería" refers to the natural tendency of an olive tree to produce a large crop one year followed by a smaller crop the following year.
In other words, a large olive harvest in one year is often followed by lower production the next, as the tree needs time to recover.
We have always thought that alternate bearing was partly due to traditional farming practices, in which the harvest was delayed in order to achieve the highest possible oil yield. We believed that this delay prevented the olive tree from recovering in time, combined with a possible deficit of nutrients needed for fruit formation, particularly phosphorus.
However, we have gradually come to think that alternate bearing, although it can be reduced through modern agricultural practices, is an inherent characteristic of the crop.
Agronomic care
This section covers the proper use of fertilizers and treatments.
However, pruning deserves a special mention, as it is one of the most debated and subjective aspects of olive cultivation.
Olive tree pruning is always an interesting topic of discussion among farmers because there are many different approaches.
There are many types of pruning: crown formation, maintenance pruning, rejuvenation pruning and, essentially, almost any adjective you can think of.
Pruning is essential for making the best possible use of all the resources available to the olive grove and directing them towards olive production.
The overall objective of pruning is to create an orderly, well-ventilated tree crown that receives sufficient sunlight for the proper development of the greatest possible number of fruits.
The strategies and techniques used to achieve this objective can be found in any good olive-growing manual, although different approaches and criteria are gradually becoming more closely aligned.