How to Successfully Establish a Pistachio Orchard

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Establishing a Profitable Pistachio Orchard

In this article we will explore how to establish a pistachio orchard from scratch, covering everything from soil to harvesting. Pistachio is a highly profitable crop, and in recent years, the number of pistachio orchards has been increasing worldwide. However, before establishing a pistachio orchard, it is essential to conduct thorough research on the specific requirements needed for successful cultivation. In this article, we will explain the key factors involved in the establishment of a pistachio orchard.

Pistachio Tree Soil Requirements

Pistachio trees thrive in sandy loam and loam soils, with an ideal pH range between 7.0 and 7.8. To know your soil type click here. These soil types promote healthy root growth and allow for efficient water absorption while reducing the risk of waterlogging, a condition pistachio trees are particularly sensitive to.

Pistachio Tree Climate Conditions

Pistachio trees are best suited for arid, semi-desert climates characterized by long, hot, and dry summers with low humidity. They also require cool winters, though not excessively cold. The trees benefit from summer temperatures around 37°C, which help produce high-quality, abundant nuts (pgai.com.au).

Pistachio Cultivars

The following are cultivars of the species Pistacia vera L. (UC Davis Fruits and Nuts):

  • Kerman: The main female cultivar, introduced in 1957, known for producing large yields of light greenish-yellow kernels with a mild flavor. It has a strong tendency toward alternate bearing and can produce a high number of blanks in some years. Kerman is also prone to a significant number of non-split nuts, and its late maturity can increase exposure to the third flight of navel orangeworms.
  • Golden Hills: This female cultivar, released in 2005, offers similar yields and kernel sizes to Kerman but with fewer blanks and a higher percentage of edible, in-shell split nuts. It flowers about one week earlier than Kerman and also matures one week earlier. Ongoing evaluations continue to assess its performance.
  • Lost Hills: Another female cultivar released in 2005, it is similar to Kerman in terms of yield but produces larger kernels. Like Golden Hills, it has fewer blanks and a higher proportion of edible, in-shell split nuts. Lost Hills flowers approximately one week earlier and matures about 10 days earlier than Kerman. Further evaluations are ongoing.
  • Peters: The primary male cultivar, Peters produces abundant pollen, which is shed over a period of more than two weeks. Its pollen durability is considered strong, though under low-chill conditions, it may shed pollen later, leading to inconsistent pollination of Kerman.
  • Randy: A male cultivar that flowers about 10 days earlier than Peters. Randy’s bloom period aligns more closely with that of Golden Hills and Lost Hills but is too early to serve as the primary pollinizer for Kerman. Its bloom period is similar in length to Peters, and it is noted for having more durable pollen.

California Pistachio Rootstocks

The commercial pistachio species, Pistacia vera L., is cultivated on various rootstocks derived from different Pistacia species or their hybrids. In trials assessing economic production over the first five years, Kerman trees grafted onto UCB I rootstock produced the highest yields. Kerman on Pioneer Gold I rootstock yielded approximately 85% of what was achieved with UCB I.

Pioneer Gold I (PG I): This rootstock, derived from P. integerrima, is the most commonly used. It demonstrates good tolerance to Verticillium wilt but is the least tolerant to cold, as seen in trials with temperatures dropping to 4–12°F in the winter of 1989-1990. It is also less tolerant of salinity compared to UCB I and Atlantica, though it can handle up to 5,120 PPM of total dissolved solids (TDS). However, its high uptake of sodium and chloride may contribute to lower yields compared to other rootstocks. Additionally, PG I is prone to zinc and copper deficiencies.

UC Berkeley I (UCB I): This hybrid rootstock, a cross between P. atlantica and P. integerrima, is widely used in pistachio cultivation. It is resistant to Verticillium wilt and offers better tolerance to salinity but can experience deficiencies in zinc, copper, and boron.

Atlantica: This rootstock, derived from P. atlantica, is less commonly used today due to its susceptibility to Verticillium wilt. However, it is the most tolerant to salinity and is highly cold-tolerant, which is particularly beneficial during the early stages of orchard establishment. (UC Davis Fruits and Nuts)

  • Pioneer Gold I (PG I): This rootstock, derived from P. integerrima, is the most commonly used. It demonstrates good tolerance to Verticillium wilt but is the least tolerant to cold, as seen in trials with temperatures dropping to 4–12°F in the winter of 1989-1990. It is also less tolerant of salinity compared to UCB I and Atlantica, though it can handle up to 5,120 PPM of total dissolved solids (TDS). However, its high uptake of sodium and chloride may contribute to lower yields compared to other rootstocks. Additionally, PG I is prone to zinc and copper deficiencies.
  • UC Berkeley I (UCB I): This hybrid rootstock, a cross between P. atlantica and P. integerrima, is widely used in pistachio cultivation. It is resistant to Verticillium wilt and offers better tolerance to salinity but can experience deficiencies in zinc, copper, and boron.
  • Atlantica: This rootstock, derived from P. atlantica, is less commonly used today due to its susceptibility to Verticillium wilt. However, it is the most tolerant to salinity and is highly cold-tolerant, which is particularly beneficial during the early stages of orchard establishment.
  • Terebinthus: Once a more commonly used rootstock, P. terebinthus is no longer a popular choice due to its vulnerability to Verticillium wilt. It shares similar cold tolerance to Atlantica. (Source: UC Davis Fruits and Nuts)

Irrigation for Pistachio Trees

Pistachios are well-suited to dry climates, allowing them to endure prolonged drought periods due to their exceptional tolerance to arid conditions. However, irrigation significantly enhances both the quantity and quality of pistachio production, reduces unproductive periods, and improves harvest consistency. Excessive water stress can lead to smaller, shrunken pistachios, while over-irrigation may result in larger nuts that sacrifice quality. Drip irrigation is the most effective method, particularly during the initial planting years. In Mediterranean climates, young pistachio trees typically require between 1,000 and 1,500 m³/ha of water during the growing season, with mature trees needing as much as 3,000 to 6,000 m³/ha. Given their drought tolerance, irrigation can be moderated during times of limited water availability, focusing on key growth phases, such as fruit set and seed growth, when water demand is highest (Irritec).

Fertilization of Pistachio Trees

To implement a fertilization program, it is recommended to conduct a soil analysis. This approach ensures optimal nutrition for the pistachio crop and enables targeted management actions to improve specific soil parameters. Additionally, performing foliar analyses, particularly in late July or early August, is advisable to monitor the crop’s nutrient status and proactively address any deficiencies in essential elements (Fertilizantes y Abonos).

Nitrogen Requirements: Pistachio trees have moderate nitrogen needs. It is advisable to apply nitrogen in split doses throughout the growing season, with the majority of the application occurring in late winter or early spring, just before bud break.

Phosphorus and Potassium Ratios: The application of phosphorus and potassium should be based on soil test recommendations. These nutrients are vital for flowering, fruit development, and the overall vigor of the tree.

Micronutrient Supplements: Regularly monitor the levels of micronutrients and provide supplements as necessary. Foliar sprays containing iron, zinc, and manganese can effectively address any deficiencies.

Schedule fertilizer applications according to the growth stages of the tree. For instance, apply nitrogen before bud break, followed by phosphorus and potassium during the flowering phase, and a balanced fertilizer in late summer. The frequency of fertilization should be adjusted based on the age and health of the trees. Young pistachio trees may need more frequent applications, while established, mature trees could benefit from fewer, but more substantial doses. Regularly monitor the trees for any signs of nutrient deficiencies, such as yellowing leaves or stunted growth, and modify your fertilization regimen as needed (Stark Bros).

Pistachio Tree Pruning

The First Year
  • Planting: Unbudded rootstocks, approximately one year old, should be planted in the orchard between January and early May. After planting, the trees should be staked and irrigated immediately. A regular fertilization and irrigation program should be implemented to encourage vigorous growth.
  • Staking: Stakes should be manually positioned next to the root ball, not inserted into it. Use 2 x 2 inch stakes, 6 feet long, and drive them 12 to 18 inches into the soil. Position the stake so that the tree leans against it in the direction of the prevailing wind.
  • Field Budding: Pistachio scions are usually budded onto the rootstock in early summer, continuing as long as the bark of the rootstock is pliable. The most common method is T-budding, performed at a height of 24 to 28 inches. The harvester attaches at 19 to 22 inches, so the bud should be placed above this zone.
  • Caution: Avoid attempting to prune the scion shoot to promote the growth of primary scaffolds (the initial branches) during the first growing season, as the short lateral branches that develop will not be suitable for scaffolding during dormant pruning and are typically removed, resulting in no benefit.
  • First Heading Cut: The scion shoots should be cut back to 42 inches during the first dormant season. This cut will encourage more lateral branching than a cut made during the growing season. If the tree does not reach 42 inches in its first season, the first heading cut should be made during the second growing season. A tree with two scaffolds may result, but it is usually not as strong as one with three scaffolds.
The second Year

Trees in their second year will typically develop several growing laterals that will become primary scaffolds, which should be tied in a vase-like shape to keep them upright. These branches should be pinched during the growing season to 14 inches. Allow secondary branches to grow to maximize canopy area and increase the girth of the developing scaffolds. Avoid developing secondary and tertiary branching in the same season, as heading the secondaries could make the tree spindly and more prone to injury.

  • Branching Improvement: The branching of primary scaffolds can be enhanced by clipping the leaf blade from its petiole at the second node from the terminal.
  • Lateral Growth Management: Pinch lateral growth on both the rootstock and scion, and remove any growth close to the ground that may be affected by herbicides.
Second Dormant Season Pruning
  • Thin secondary branches to retain 2 to 3 branches per primary. Selected branches should not be positioned directly opposite each other.
  • Head the secondaries to 11 to 13 inches and tie them in an upright vase shape.
Year 3-5

Trees will now have primary scaffolds branching into secondaries and then tertiaries. Allow these to grow.

Third Dormant Season Pruning
  • For each secondary scaffold, thin the tertiary branches. Select which branches to keep based on their strength and position. Follow the Ratio Pruning method: retain 2 secondary branches for each primary and 2 tertiary branches for each secondary.
  • Use tape to mark your pruning shears at 16 and 22 inches for measuring branch lengths during pruning. Measure from the origin of a secondary branch out to the tertiary. If the branches are vigorous, head the tertiary where this total length is 22 inches; if weak, head it at 16 inches.
  • Tie up the tertiaries high on the branch, including cross-tying within the canopy. Avoid opening the center of the tree, as this can reduce early fruit-bearing potential.
  • Some fruitwood branches may develop down the scaffolds. Another aspect of Ratio Pruning is to maintain one fruitwood branch for each structural branch.
Years 6 – 8

Once the basic tree shape is established, reduce the number of pruning cuts to enhance and distribute spur development, which promotes fruitfulness.

Dormant Season Pruning
  • For trees just entering production, pruning mainly involves small heading cuts to develop the canopy and strengthen the fruiting wood. Heading cuts on one-year-old whips can help increase canopy area. Vigorous whips should be cut to 18 to 22 inches, while weaker whips should be cut to 16 inches.
  • Use heading cuts to tip the fruitwood to strengthen it, ensuring that vegetative buds remain above the fruiting buds to encourage branching.
  • Prune any branches that may obstruct harvesting equipment.
  • The ‘knuckle cut’ can be beneficial for nut production. A knuckle is a ‘whorl of buds’ formed by compressed internodes. A cut just above the knuckle will promote multiple branches with flower buds, especially useful on flat limbs, but not ideal for building structure.
  • The tree should be divided into zones based on primary scaffolds, and some thinning cuts may be necessary to keep wood within their designated zones.
Mature Trees

The main goal of pruning mature trees is to confine them within their allocated space while promoting light penetration for effective nut production throughout the tree. Due to apical dominance, the most vigorous shoots emerge from buds closest to the terminals, adding growth to the upper canopy and lateral margins. Over time, main bearing limbs tend to grow less upright, limiting light penetration to lower fruiting wood, resulting in a crop that is higher in the canopy and harder to harvest.

Pruning for mature trees begins at ground level using hand shears. For the upper canopy, switch to pole pruners.

Dormant Season Pruning
  • Perform thinning cuts to remove broken and closely overlapping branches, preserving the higher branch when removing overlaps.
  • Make thinning cuts to elevate bearing branches; the remaining branches should be directed upwards rather than outwards. These cuts are usually made on the outer edges of the tree.
  • Heading cuts on one-year-old whips are fewer in older trees.
  • Tip the fruitwood as needed.
  • For saw cuts, use a hand saw to remove lower limbs that no longer produce fruiting wood. Start with an undercut about an inch from the scaffold, then cut from the top. Saw just beyond the ‘bark inclusion layer’ to encourage callus tissue formation for healing the wound (UC Davis).

Pistachio Trees Pollination

Pistachio trees are dioecious, meaning they have separate male and female trees. Male trees produce pollen, while female trees bear the fruit. The flowers are small and inconspicuous, typically appearing in clusters. Male flowers produce pollen, and female flowers are responsible for fruit development. Pistachio trees primarily rely on wind for pollination. Pollen is dispersed by air currents from male trees to the receptive female flowers. Female flowers generally bloom later than male flowers, allowing for maximum pollen release and increasing the chances of successful pollination. It is essential to plant compatible male and female cultivars for optimal pollination and fruit set. The Kerman cultivar is one of the most widely grown female cultivars and is often pollinated by male cultivars such as Peters or Randy. Having a sufficient number of male trees (typically at least 10% of the total trees) in proximity to female trees is recommended to ensure adequate pollen availability. Successful pollination usually occurs in late spring, around May, when both male and female flowers are open. Warm and dry weather during flowering enhances pollination success, while excessive rain or high humidity can negatively affect pollen viability and fertilization.

Pistachio Trees Harvesting

Timing of Harvest
  • Maturity Indicators: Pistachios are typically ready for harvest when the hulls begin to split open, exposing the nuts inside. This usually occurs in late summer to early fall, around September to October, depending on the climate and specific cultivar.
  • Seed Color Change: The nuts inside should also be fully developed, with the seed changing color from green to a light beige or pale yellow.
  • Weather Conditions: Dry weather conditions are ideal for harvesting, as they help to reduce the moisture content of the nuts, which can lead to better quality and lower risk of spoilage.
Harvesting Methods
  • Shakers: Mechanical shakers are commonly used to harvest pistachios. These machines apply a shaking motion to the tree, causing the ripe nuts to fall onto the ground. This method is efficient and can cover large orchards quickly.
  • Manual Collection: In smaller orchards or for higher quality control, nuts may be harvested by hand. Workers use hand-held tools to remove the nuts from the branches gently. Hand harvesting allows for better selection of high-quality nuts and minimizes damage to the tree.
Post-Harvest Handling
  • Cleaning: After harvesting, the nuts should be cleaned to remove any debris, hulls, and shells. This can be done using air blowers or sieves.
  • Drying: Nuts should be dried to reduce moisture content to around 6-8%. This is essential for preventing mold and prolonging shelf life.
  • Storage: Store harvested nuts in a cool, dry place, ideally in airtight containers, to maintain freshness and quality.

Yield Considerations

  • Average Yields: Yields can vary significantly depending on the age of the trees, cultivar, and growing conditions. Mature trees can produce anywhere from 1,000 to 2,500 pounds of nuts per acre.
  • Factors Affecting Yield: Weather conditions, pollination success, and overall orchard management practices all play a crucial role in determining the final yield.
Sources
  1. PGAI (Pistachio Growing Association International): pgai.com.au
  2. University of California, Davis: fruitsandnuts.ucdavis.edu
  3. Irritec – Drip Irrigation for Pistachio Trees: irritec.com
  4. Stark Brothers – Fertilizing Pistachio Trees: starkbros.com
  5. Fertilizantes y Abonos – Fertilization Plan for Pistachio Trees: fertilizantesyabonos.com