Today, we delve into a technical topic that is close to the hearts of many enthusiasts – the pruning of the olive tree. The olive tree is undoubtedly one of the most widespread trees in our countryside and has always been connected to our territory. Proper pruning is one of the essential aspects for the rational and productive growth of this tree. Pruning the olive tree correctly allows for a good yield of fruits and perhaps even producing excellent extra virgin olive oil on one’s own.
In this article, we will explore the different olive orchard management forms and how the olive pruning interventions are carried out at various stages during the long life of this precious tree.
The Olive Tree
The olive tree, scientifically known as Olea europaea, is one of the oldest fruit-bearing plants used for human consumption. It is native to countries bordering the Mediterranean and belongs to the botanical family Oleaceae.
It is a very long-lived tree that goes through different life stages. The development phase after planting lasts for about four years. From four to eight years, if the tree has been well cared for, irrigated during dry periods, fertilized with cover crops, and pruned correctly, it begins its first productive phase. The production increases over time.
From eight years, the olive tree enters its maturity, which lasts about 40-50 years, during which the productions stabilize. From the age of 50-60 and onwards, it enters the aging phase. In favorable soil and climate conditions, the plant can live for hundreds of years.
The Root System and Trunk
The root system of the olive tree is quite shallow, usually not extending beyond one meter in depth. However, the roots spread extensively horizontally. The tree has a cylindrical trunk, gray in color, and a contorted shape. The olive wood is one of the best, being hard and heavy. At the base of the trunk numerous basal shoots are generated each year, which need to be eliminated using appropriate pruning tools.
Branches and Leaves
The olive tree is an evergreen tree, with continuous vegetative activity that slows down only during the winter period, while the leaves are arranged oppositely on the branches and have an elliptical shape, being leathery with a small petiole. The lower side of the leaves is white-silvery, while the upper side is usually green and the buds, from which new branches develop, come in two types:
- Terminal buds, which continue the plant’s growth
Finally, the buds can also be:
- Wood buds, which give rise to vegetative organs such as shoots and leaves
- Flower or fruit buds, which give rise to reproductive organs
- Mixed buds
Flowers and Fruits
The flowers are hermaphroditic, small, and white in color, grouped in clusters ranging from 10 to 15. The tree emits its inflorescences, known as “mignole”, on the axils of the previous year’s branches. Depending on the climatic zone, flowering begins between March and April, and depending on the variety, it can start from May and last until June at the latest.
The fruits, known to all, are the olives: globose drupes with different shapes, colors, sizes, and possible uses depending on the chosen variety. It is a very important drupe for the Italian agricultural sector. In Tuscany alone, there are at least 79 autochthonous varieties. More generally, many Italian varieties are listed in the PDO (Protected Designation of Origin) products’ registry.
Why Olive Pruning Is Important
Let’s debunk a common myth, which is that olive trees won’t produce if they are not pruned. This is not true. In fact, in olive tree cultivation, pruning is crucial for various reasons. What is true is that a well-pruned olive tree increases its production and makes harvesting easier. The first problem faced with an unpruned olive tree is related to harvesting.
Olive trees tend to grow upward in their natural form. Imagine an 8-meter-tall tree; harvesting the fruit becomes challenging and laborious in such cases. While it is possible to harvest olives by hand when dealing with limited production, using manual shakers or olive harvester that can reach up to 4 meters in height is much more convenient.
Harvesting in this manner results in higher-quality olive oil, as the olives are picked while still on the tree and are green. It is true that some argue that the beneficial properties of extra virgin olive oil are still to be fully proven.
When fruit collection is difficult due to the tree’s height, one must wait for the olives to fully ripen and fall to the ground naturally. However, this method poses risks of the olives getting damaged and compromising the oil quality. Therefore, the objectives of olive tree pruning are:
- Preserving the full efficiency of the tree’s canopy
- Rationalizing growth and the number of fruit-bearing branches, considering the olive harvesting technique used
- Maintaining a balanced ratio between leaf surface area and the tree’s wood
- Ensuring optimal air circulation within the canopy, which should also be well-exposed to sunlight
- Regulating excessive productivity to avoid alternating production cycles.
Olive Pruning at Different Growth Stages
Pruning interventions for olive trees vary depending on the tree’s life stage. In the early years when the plant is growing and taking its shape, the pruning will be minimal. In the adult-youth phase when production is steady, a moderately intensive pruning is performed. During the tree’s aging phase when the alternating production phenomenon is more significant, more drastic pruning is carried out.
When to Prune Olive Trees?
Two types of olive tree pruning can be distinguished based on the time of the year when they are performed:
- Dry pruning or winter pruning, which includes most of the pruning operations. This type is carried out during the vegetative rest period, between January and March. However, if trees are damaged by excessive snow, it is advisable to wait for the vegetative recovery before proceeding to assess the tree’s ability to grow.
- Green pruning or summer pruning, limited to the removal of basal shoots and suckers. This type is performed between April and July.
How to Perform Olive Pruning
Now let’s go through the various operations involved in olive tree pruning.
Training Pruning to Shape the Olive Tree
The first olive tree pruning operation is known as “training pruning”. This type of intervention is often carried out in nurseries. During the training pruning, the shape that the tree should take in the future is set on the young plant.
Polyconic Vase Shape
Among the different training forms for olive trees, the polyconic vase shape is one of the most common. The trunk is cut (headed) at a height of 100-110 cm, and 3 or more main branches are allowed to grow outward from this point, giving the tree its final shape. The polyconic vase shape allows excellent aeration of the canopy, avoiding excessive thickening of vegetation. After the training pruning, the formation pruning follows, which further shapes the desired form by eliminating shoots from the plant below the heading point, which might interfere with the planned training shape.
Another form, although less common, is the bush shape. This shape is achieved by not performing any pruning intervention for the first 8-10 years of the tree’s life. An exception is the thinning of small basal shoots within the first 50 cm, which should be done after transplantation or at the end of the first year. Once the plant has developed, a bush with a globoid shape and various tops is obtained. It is then controlled in height through more or less drastic pruning from the 10th year onwards. This way, a shape very similar to the one an olive tree has in nature is achieved. Periodic pruning is necessary for this shape, involving the cyclical removal of trees from the entire plantation.
Similar to the bush shape is the globe training shape, where the main trunk is pruned at 60-80 cm above the ground. Branches develop from this height without a defined order, reaching different heights with their branches. Over the years, the plant assumes a globular shape.
Bush Vase Shape
There are also low-training shapes, such as the bush vase shape, achieved either by pruning the plant at a height of 60-70 cm above the ground and letting 3-4 branches incline outward, or by planting 3-4 trees close together, not more than one meter apart. The plant is kept low with subsequent prunings, favoring outward rather than upward branching.
Single Trunk Shape
Finally, we have the single trunk training shape, which involves simpler pruning operations. To set the plant with this training form, formative prunings are carried out during the first two years of life, eliminating basal branches within the first 90-100 cm. In the single trunk shape, main branches are distributed helically along the trunk, decreasing in length from bottom to top. The top is significantly lightened to avoid shading the lower part.
Generally, all training and formative pruning operations are performed during the dry or winter pruning period.
Pruning Olive Trees in Production
Production pruning is performed on mature olive trees and serves several purposes. The main objective is to renew fruit-bearing branches by completely removing or shortening a certain number of branches, limiting competition within the canopy. Production pruning is carried out both in winter and during the spring-summer period. In the former case, operations involve lightening the canopy and the tops through heading cuts (dry pruning). In the latter case, basal shoots and suckers are removed (green pruning). Keep in mind that olives bear fruit on second-year branches, and suckers can also be removed during the winter period.
The fruit-bearing branches are the “fruiting shoot” and the “mixed branch”. Vegetation is lost on wood that is two years old or older since normal vital buds are not present. However, despite the old wood, the plant rebalances itself as it can produce new shoots from latent buds.
On the mixed branches, terminal buds and the first pairs of sub-terminal buds develop into wood. As the branch continues to grow, it starts to weigh down and bend downwards, forming the so-called fruiting spur, which are the best fruit-bearing structures. At the maximum bending point, new shoots are emitted from the fruiting spur. Some of these shoots will be removed, while others will serve to replace the same fruiting spur when it has exhausted or stretched too far. Pruning olive trees for production must take these peculiarities into account, allowing for the gradual and periodic rejuvenation and bringing together of the fruiting foliage of the mother branch.
As for suckers, they are sometimes left to replace old or damaged branches.
Proper production pruning achieves the goals of better vegetation distribution on the plant, maintaining the chosen training shape, and stimulating the formation of new fruit-bearing branches.
Reform Pruning or Rejuvenation Pruning of Olive Trees
Other olive tree pruning operations include reform or rejuvenation pruning. These types of pruning are performed when you want to modify the tree’s shape or rejuvenate it if it is too old.
In these cases, vigorous cuts are made during the winter period. These cuts serve to eliminate one or more branches, depending on whether the goal is to restore the plant’s training shape or rejuvenate it.
In these cases, old branches can be replaced with suckers, and in more difficult cases, even with basal shoots.
These can be extraordinary operations required due to natural events such as a fire or severe frosts.
Renewal pruning also falls under this type of operation. This pruning aims to remove dead or severely damaged wood due to diseases such as the lupa or olive tree decay.
Reform or rejuvenation pruning is a very laborious operation that requires time to yield results. Several interventions are needed in subsequent phases. In the end, however, this technique will give the olive tree a second youth.
Additional Considerations for Proper Olive Pruning
In a previous article, we provided a comprehensive overview of the best tools to use for pruning. For correct olive pruning, we suggest taking a look at that article. Remember that saws, axes, and scissors should always be kept sharp.
Another suggestion is to perform pruning operations when there is no risk of rain. Moreover, it is essential to treat larger cuts with poltiglia bordolese (permitted in organic farming) and suitable mastics to prevent infections.
Finally, we recommend using caution when you have to climb the tree to perform cuts. Falls from olive trees are among the most frequent accidents in our fields. It’s better to use specific lightweight aluminum ladders that can be well-anchored to the ground, rather than venturing (with hands busy) into precarious balance situations.
- OUP Academic – “Centennial olive trees as a reservoir of genetic diversity”: A study on the genetic characterization of ancient olive trees in southern Spain, revealing a priceless reservoir of genetic diversity.
- Scientific American – “The Origins of the Olive Tree Revealed”: DNA analysis shows that the olive tree was first domesticated in the Eastern Mediterranean between 8,000 and 6,000 years ago.
- ScienceDirect – “Demystifying the age of old olive trees”: Research challenging the belief that monumental olive trees are several centuries old, showing most may have maximum ages between 300 and 500 years.
- Pablo Báez-González, …, Carlos Bordons – ScienceDirect – “Chemometric Classification of Cultivars of Olives: Perspectives on Portuguese Olives”: Discusses the importance of distinguishing and identifying olive cultivars, using morphological features and chemometric multivariate classification techniques.
- Encyclopedia Britannica – “Olive | Description, Production, & Oil”: Comprehensive overview of the olive tree and its fruit, discussing history, physical description, and methods of cultivation and oil production.
- Mdpi – “Energetic Valorisation of Olive Biomass: Olive-Tree Pruning, Olive Stones and Pomaces“: The olive oil industry, producing over 20 million tons of olives annually, generates significant by-products like olive-pruning debris and stones. Though potentially harmful to the environment, these by-products can be converted into energy through processes like combustion and gasification, aligning production with environmental conservation.