The Importance of Green Pruning in Pistachio: Objectives, Techniques, and Optimal Timing

At Agro Vivero del Mediterráneo, we have spent years dedicating ourselves body and soul to the fascinating world of pistachios. Our field experience has taught us that the success of an orchard does not lie solely in choosing a good plant or in proper irrigation. There are a series of agronomic practices that, when carried out with precision and knowledge, make the difference between a mediocre orchard and a highly productive and profitable operation. One of these practices, often underestimated but of vital importance, is green pruning. 🌳✂️

Throughout this article, we will immerse ourselves in the universe of green pruning in pistachio trees. We will share with you, from our perspective as technicians and producers, why it is so crucial, what its main objectives are, what techniques we use to carry it out, and, above all, what the perfect time is to do it. We want to demystify this task and provide you with the necessary tools so that you can apply it correctly in your orchards and thus maximize their potential.

At Agro Vivero del Mediterráneo, we are convinced that shared knowledge is the key to the collective success of the sector. Join us on this technical journey and discover how proper green pruning can transform your pistachio trees and secure the future of your investment.

What is Green Pruning and why is it so crucial for pistachios?

Green pruning, also known as summer pruning, encompasses all those cutting operations we perform on the vegetative part of the tree during its active growth period, that is, from spring bud break until leaf fall in autumn. Unlike winter or dormant pruning, which focuses on the main structure of the tree and production, green pruning has a more selective and refining nature.

We might think it is a secondary job, but nothing could be further from the truth. In the pistachio tree, a tree with very particular growth characteristics, green pruning becomes a fundamental strategic tool. Why? Mainly because it allows us to direct the tree’s energy to where we are really interested: the formation of a strong and balanced structure, proper canopy illumination and aeration, and the promotion of flower bud production for future harvests.

A young pistachio tree that is not subjected to proper green pruning tends to grow uncontrollably, generating a large number of unnecessary branches that compete for resources (water, nutrients, and light). This not only delays its entry into production but also hinders the formation of a well-structured vase or central leader, which in the long run will complicate harvesting and other agricultural tasks, directly affecting the profitability of the orchard.

In adult trees, green pruning is equally important. It helps us maintain the balance between vegetative growth and production, eliminate suckers that drain vigor from the tree, improve light penetration and phytosanitary treatments, and reduce the risk of fungal diseases by improving ventilation. It is, in short, a fine-tuning task that ensures we have healthy, well-formed, and highly productive trees year after year.

Fundamental Objectives of Green Pruning in Pistachio

When we put on our gloves and grab our shears in summer, we don’t do it randomly. Every cut has a purpose, an intention. At Agro Vivero del Mediterráneo, we have defined a series of key objectives that we pursue with green pruning. These objectives vary slightly depending on the age of the tree, but essentially, they seek to optimize its development and production.

1. Tree structure training (Years 1-4) 🌳

This is, without a doubt, the primary objective during the first years of the orchard’s life. The pistachio tree is a tree that needs to be guided to form a vase or central leader structure that is productive and, at the same time, facilitates mechanized tasks.

• Selection of main branches: During the first and second green pruning (summer), it is crucial to select the 3 or 4 branches that will make up the main structure of the vase. These must be well distributed around the trunk, with a good insertion angle (between 45º and 60º) to prevent future breakage due to the weight of the harvest. We will eliminate all other branches that compete with them, especially those that grow vertically with great vigor (suckers) or those located below the graft union.

• Canopy balance: Once the main branches are selected, we must ensure they grow in a balanced way. If one of them stands out with much more vigor than the others, we can pinch it (cut the tip) to slow its growth and redirect the sap towards the weaker branches. We aim for a symmetrical and open canopy.

• Removal of poorly located shoots: Throughout the summer, the tree will send out numerous shoots from the trunk and main branches. We must systematically remove all those that grow towards the inside of the canopy, those that cross with others, those that emerge from the base of the trunk (root suckers), and those located below the crotch or insertion point of the main branches. This work, known as shoot thinning or desuckering, is fundamental to avoid a tangle of unnecessary branches and ensure that energy is concentrated on forming the structure we have designed.

Proper training during the first few years is the best investment we can make. A tree well-formed from the start is a tree that will enter production sooner, will be easier to manage, and will have a much longer and more profitable productive life. Choosing a quality pistachio plant is the first step, but guiding it with proper training pruning is what guarantees success.

2. Vigor control and vegetative-productive balance 🌿💪

In already formed trees in full production, green pruning seeks to maintain a harmonious balance. The pistachio tree has a natural tendency towards alternate bearing, that is, alternating years of abundant harvest with years of scarce harvest. A well-executed green pruning can help us mitigate this phenomenon.

• Removal of suckers (water sprouts): Suckers are very vigorous, vertically growing branches that sprout on the main branches or the trunk. They are true energy “thieves.” They do not produce nuts and consume a large amount of sap and nutrients that should go towards the development of the pistachios and the formation of flower buds for the following year. Their systematic removal during the summer is one of the most important tasks of green pruning in adult trees.

• Thinning of mixed shoots: In heavy crop years, we can perform a light thinning of the shoots bearing the pistachios. This not only improves the size and quality of the remaining nuts but also allows the tree to allocate more resources to floral induction for the next year’s harvest, helping to regularize production.

• Control of excessive growth: If we observe that the tree is developing exaggerated vegetative growth to the detriment of production, we can act by pinching some terminal shoots. This slows down growth in length and encourages lateral branching and the formation of flower buds.

3. Improvement of illumination and aeration ☀️🌬️

A well-lit and ventilated canopy is synonymous with a healthy and productive tree. Light is the engine of photosynthesis, the process by which the tree generates the energy it needs to grow and produce.

• Opening of “windows”: By removing branches that grow towards the inside of the canopy or that cross each other, we create “windows” that allow sunlight to enter the innermost parts of the tree. This is fundamental for the uniform ripening of the nuts and, more importantly, for the correct differentiation of flower buds. A bud that does not receive enough light will hardly become a flower the following year.

• Disease prevention: Good aeration hinders the proliferation of fungal diseases such as Alternaria or Botryosphaeria, which thrive in humid and shady environments. By facilitating air circulation, we ensure that leaves and clusters dry more quickly after rain or dew, creating a less favorable microclimate for pathogens.

• Effectiveness of treatments: A more open canopy allows applied phytosanitary products to reach all parts of the tree, including the interior, improving the effectiveness of treatments and reducing the amount of product needed.

If you need personalized advice on how to apply these techniques in your orchard, do not hesitate to contact our technical team. We will be happy to help you through our consulting services.

Specific Green Pruning Techniques

Now that we know the objectives, let’s detail the specific operations we perform. It is important to have the right tools, well-sharpened and disinfected (with a 10% bleach solution or alcohol) to make clean cuts and prevent the transmission of diseases.

Shoot thinning or desuckering

It consists of the removal of herbaceous (tender) shoots that appear in unwanted areas of the tree. It is one of the most repetitive but essential tasks of green pruning, especially in young trees.

• What do we remove?

  • Root suckers: Shoots that sprout at the base of the trunk, below the graft union. It is crucial to remove them as soon as they appear, as they come from the rootstock and drain a lot of vigor from the graft (the variety we are interested in).

  • Trunk shoots: All shoots that emerge on the trunk below the crotch where we want to form the main branches (generally, at a height of 1.0 – 1.2 meters from the ground).

  • Poorly oriented shoots: Those that grow towards the inside of the canopy, in direct competition with well-positioned main or secondary branches.

• How do we do it? Being tender shoots, many of them can be easily removed by hand, without the need for shears. This work must be done in several passes during the spring and summer, as the tree does not stop sending out these shoots.

Pinching or tipping

This technique consists of cutting the tip of a growing shoot. With this we achieve several effects:

• Slow down apical growth: By removing the terminal bud, we break apical dominance and temporarily stop the growth in length of that branch.

• Encourage lateral branching: The removal of the terminal bud stimulates the development of the axillary buds located immediately below the cut, which gives rise to new lateral branches. This is very useful for “filling in” areas of the canopy that are sparse.

• Balance vigor: As mentioned before, we use it in young trees to slow the development of a main branch that is growing much more than the others, seeking a symmetrical development of the canopy.

• Induce production: In some varieties, pinching the current year’s shoots can favor the transformation of vegetative buds into flower buds for the following season.

Pinching should be done when the shoot is still tender, cutting about 2-3 cm from the tip.

Removal of suckers (water sprouts)

It is a task similar to shoot thinning, but it focuses on branches of exceptional vigor.

• How to identify them? They are branches that grow very vertically, with very long internodes and large leaves. They usually appear on the upper part of the main branches, near areas where significant pruning cuts were made in winter.

• How to remove them? It is essential to cut them at the base, as close as possible to the insertion branch, without leaving a stub. If they are very large and already lignified (woody), we will have to use loppers or a pruning saw. Leaving a stub would cause the emission of new suckers around the cut, aggravating the problem.

Fruit and shoot thinning

Although less common than the previous ones, it is a technique to consider in years of very marked alternate bearing with an excessive crop load.

• Cluster thinning: It consists of removing some of the pistachio clusters to reduce competition among them. The worst positioned, the smallest, or those found on very weak branches are usually removed. The objective is to improve the size and the split percentage of the nuts we leave on the tree and reduce plant exhaustion.

• Shoot thinning: In extreme cases, an entire mixed shoot can be removed if the density is very high, to improve light penetration and favor the rest of the structure.

These decisions must be made with highly refined technical criteria, analyzing the tree’s crop load and vigor. If you are thinking of starting an orchard and want to ensure good management from the beginning, you can request a quote and reserve your plants with us.

The Optimal Timing: When to Perform Green Pruning? 🗓️

Just as important as knowing what to cut is knowing when to do it. Performing green pruning at the wrong time may not have the desired effect or may even be counterproductive. The “when” is not a fixed date on the calendar, but depends on the phenological stage of the tree and the objectives we pursue.

In general, the period for green pruning ranges from late spring to mid-summer. We can divide it into two main phases:

Phase 1: Late Spring (May – June)

This is the time of maximum vegetative growth for the pistachio tree. The sap flows strongly and the tree is constantly sending out shoots. It is the ideal period for:

• Shoot thinning and root sucker removal: It is now when we must be most insistent. Ideally, make several passes through the orchard (every 15-20 days) to remove all unwanted shoots while they are still tender. Doing it this way is fast, does not create large wounds, and prevents the tree from wasting energy on useless growth. If we let these shoots lignify, their removal will be more costly and the resulting wound will be larger.

• Pinching for training: It is the perfect time to select the main branches on young trees and balance their growth through pinching. The shoots are at the right length and respond very well to this technique, branching easily.

• The removal of the first suckers: The most vigorous suckers will already be evident. Removing them now allows all that energy to be redirected towards the growth of the rest of the tree and the sizing of the nuts.

Performing a good green pruning in this first phase will save us a lot of work during winter pruning. A clean and well-directed tree in summer is a tree that will need far fewer cuts in winter, which translates into savings in time and labor.

Phase 2: Summer (July – Early August)

As summer progresses, the tree’s growth slows down. The photoperiod decreases and the tree begins to allocate more resources to nut maturation and the accumulation of reserves for the following year. In this phase, our interventions must be more restrained.

• Review of shoot thinning and suckers: We will make one or two more passes to remove suckers and adventitious shoots that may have emerged late. There will no longer be such explosive growth as in spring, so it will be a review task.

• Fruit thinning: If we have decided to perform fruit thinning, the ideal time is early July, once the nuts have reached a considerable size and we can clearly distinguish which are the highest quality clusters. Doing it earlier may not be effective, and doing it later will have little impact on the final size.

• Minor corrections: It is time to make small cleaning cuts to improve the illumination of the clusters for the final ripening phase. We will remove any inner branch or shoot that is excessively shading a cluster.

What should we NOT do?

It is crucial to avoid severe pruning during late summer and early autumn (late August – September). Why?

1. Risk of new sprouting: A significant cut at this time can stimulate the tree to send out new shoots. These shoots will not have enough time to harden off (mature the wood) before the arrival of the first winter frosts, so they will burn, having meant a useless expenditure of energy for the tree.

2. Depletion of reserves: At the end of the cycle, the tree is translocating nutrients from the leaves to the branches and trunk to accumulate reserves that will allow it to sprout strongly the following spring. If we perform drastic pruning and remove a large amount of leaf mass, we will be diminishing its capacity to accumulate these reserves, which will weaken the tree for the next cycle.

3. Risk of diseases: Large pruning wounds heal more slowly as temperatures drop, increasing the risk of wood pathogens entering.

In summary, green pruning should be a continuous and light task during spring and the first half of summer, and should cease completely as we approach autumn.

Conclusions: Green Pruning as an Investment for the Future

From our experience at Agro Vivero del Mediterráneo, we can state without fear of being wrong that green pruning is one of the most profitable practices in pistachio management. It should not be seen as an expense, but as a direct investment in the productivity and longevity of our orchard. 📈

A well-planned and executed green pruning program allows us to:

• Advance entry into production: By training efficient trees from day one.

• Increase production and quality: Improving the size, the split percentage, and the health of the nuts.

• Regularize harvests: Mitigating alternate bearing and ensuring more stable income.

• Reduce long-term costs: Facilitating mechanized tasks and reducing the need for drastic winter pruning and the use of phytosanitary products.

• Extend the useful life of the orchard: Creating structurally solid and balanced trees.

We know it may seem like a complex task, but with observation, practice, and the right advice, any farmer can master it. The pistachio tree is a grateful tree that responds quickly to the care we provide. Dedicating time during the summer to guide its growth is an effort that will be more than rewarded in the form of abundant, high-quality harvests.

We hope this article has been useful to you and encourages you to give green pruning the attention it deserves. The future of the pistachio sector lies in professionalization and the application of precision agronomic techniques, and green pruning is undoubtedly one of the cornerstones of this approach. For any questions or to delve deeper into any of our services, our team is entirely at your disposal. Together we can make your orchards reach their maximum potential! 🤝🌱