Pistachio Tree (Pistacia vera)

If you are looking for a tree to produce a tasty, crunchy, and shelf-stable snack, you may consider planting a pistachio tree. As long as you live in an area that meets its very specific growing conditions: dry, hot summers and cold winters. you’ll successfully grow your own pistachio nuts.

I. Appearance and Characteristics

The pistachio (Pistacia vera), a member of the cashew family, is a small tree originating in Persia. The tree produces seeds that are widely consumed as food. The word can be countable or uncountable, meaning its plural is with or without an ‘s’.

The pistachio tree is native to regions of Central Asia, including present-day Iran and Afghanistan. .

The tree grows up to 10 metres (33 feet) tall. It has deciduous, pinnate leaves 10–20 centimetres (4–8 inches) long. The plants are dioecious, with separate male and female trees. The flowers are apetalous and unisexual and borne in panicles.

The fruit is a drupe, containing an elongated seed, which is the edible portion. The seed, commonly thought of as a nut, is a culinary nut, not a botanical nut. The fruit has a hard, cream-colored exterior shell. The seed has a mauve-colored skin and light green flesh, with a distinctive flavor. When the fruit ripens, the shell changes from green to an autumnal yellow/red and abruptly splits partly open. This is known as dehiscence, and happens with an audible pop. The splitting open is a trait that has been selected by humans. Commercial cultivars vary in how consistently they split open.

Each mature pistachio tree averages around 50 kilograms (110 pounds) of seeds, or around 50,000, every two years.

Pistachio is a desert plant and is highly tolerant of saline soil. It has been reported to grow well when irrigated with water having 3,000–4,000 ppm of soluble salts. Pistachio trees are fairly hardy in the right conditions and can survive temperatures ranging between −10 °C (14 °F) in winter and 48 °C (118 °F) in summer. They need a sunny position and well-drained soil. Pistachio trees do poorly in conditions of high humidity and are susceptible to root rot in winter if they get too much water and the soil is not sufficiently free-draining. Long, hot summers are required for proper ripening of the fruit.

• Toxicity

As with other tree seeds, aflatoxin is found in poorly harvested or processed pistachios. Aflatoxins are potent carcinogenic chemicals produced by molds such as Aspergillus flavus and A. parasiticus. The mold contamination may occur from soil or poor storage, and be spread by pests. High levels of mold growth typically appear as gray to black filament-like growth. Eating mold-infected and aflatoxin-contaminated pistachios is unsafe. Aflatoxin contamination is a frequent risk, particularly in warmer and humid environments. Food contaminated with aflatoxins has been found as the cause of frequent outbreaks of acute illnesses in parts of the world. In some cases, such as in Kenya, this has led to several deaths.

Pistachio shells typically split naturally prior to harvest, with a hull covering the intact seeds. The hull protects the kernel from invasion by molds and insects, but this hull protection can be damaged in the orchard by poor orchard management practices, by birds, or after harvest, which makes exposure to contamination much easier. Some pistachios undergo so-called “early split”, wherein both the hull and the shell split. Damage or early splits can lead to aflatoxin contamination. In some cases, a harvest may be treated to keep contamination below strict food safety thresholds; in other cases, an entire batch of pistachios must be destroyed because of aflatoxin contamination.

Like other members of the family Anacardiaceae (which includes poison ivy, sumac, mango, and cashew), pistachios contain urushiol, an irritant that can cause allergic reactions.

Pistachio Turkish delight
Large quantities of pistachios are self-heating in the presence of moisture due to their high oil content in addition to naturally occurring lipases, and can spontaneously combust if stored with a combustible fabric such as jute.

II. How to Grow and Care

Sunlight

Pistachios require full sun (8+ hours per day). Without full sun, trees will become leggy, not produce fruit, and be more susceptible to disease.

Temperature and Humidity

Optimal temperatures for pistachio trees hover at around 100 degrees Fahrenheit. In the winter, the tree requires at least 900 to 1,000 cumulative hours of temperatures between 32 and 45 degrees F to initiate new leaf and bud production. However, pistachio trees can’t tolerate temperatures below freezing or frozen ground.

Pistachio trees thrive in heat but do poorly in hot, humid climates.

Watering

Pistachio trees are very drought-tolerant and prefer arid landscapes. However, for an abundant harvest, they still require plenty of water. Water the tree deeply but infrequently, allowing the water to saturate the soil.

Excellent drainage is crucial, as pistachios do poorly in soggy soil or standing water. If you have several pistachio trees, you might want to consider an irrigation system.

Soil

Though the pistachio tree will grow in almost any soil type, it does best in light, sandy, loamy soils that are well-draining. Wet, heavy soil is not an option for these trees. Because of their long taproots, it is important that the soil reaches deep into the ground.

Fertilizing

Before adding any fertilizer, it is important to know what your soil may lack by having a soil test done. If it is lacking in nitrogen, phosphorous, or potassium, you can tailor the fertilization to fit the nutrient needs of your tree.

Apply any fertilizer in the late winter to early spring.

Planting Instructions

Pistachios grow in relatively mild climates and because of this, they can be planted throughout the year. However, the best time to plant pistachio trees is while they are dormant. Fruit and nut trees are often sold as bare root or pre-potted in late winter through early spring so that they can be planted in the ground before growth begins. Newly planted dormant trees will quickly begin to grow new roots and eventually new leaves as the weather begins to warm.

Planting pistachio trees is similar to planting most other types of trees. Begin by digging a hole twice the size of the root ball. Place the tree in hole and backfill soil into the hole ensuring that the tree remains upright and the existing soil line is maintained. If the tree is bare root, note the soil marking on the bark of your sapling and be sure to fully cover roots. Then water the tree thoroughly to remove air pockets and add additional soil as necessary.

Pruning

As with many fruit and nut trees, pistachios should be pruned in late winter or early spring before leaves have begun to appear. Begin yearly pruning by removing any dead, broken, or crossed branches. Any branches from below the graft should always be removed as well.

Pistachios can either be grown along a central leader or by the open center method, but because of their natural growth habit, pruning them into a vase shape isn’t necessary and they grow that way over time on their own.

Flowers and fruit are produced on one-year-old branches. Due to their year on/year off cycling, heavier pruning can be done on off years. To avoid infecting trees, always clean and disinfect pruning shears and saws prior to use.

Propagation

Pistachio trees are normally propagated through budding scion plant tissue onto rootstock from a disease-resistant species in the fall. This is a complicated, tricky procedure that is rarely done successfully by amateurs. Pistachio trees are not suitable for propagation by rooting stem cuttings, as the resulting tree will not have the same performance as the parent tree.

How to Grow from Seed

It is not recommended to grow a pistachio tree from seed because it is impossible to guarantee that you will get a nut-producing female tree rather than a male tree. Further, the resulting tree will have the genetic characteristics of the grafted scion plant tissue and will lack the disease resistance of the parent tree’s rootstock.

If you want to harvest our own pistachios, you are better off starting with pistachio trees from a nursery.

Potting and Repotting

These trees can be kept in containers for the first three to five years as potted nursery specimens. After this, they should be planted in the garden to allow the tree to mature. This is crucial because of the long taproot, which would be stunted with long-term container growth.

Growing pistachio trees long-term in pots, or as indoor plants, is not practical.

Pests and Diseases

Pistachio trees are highly susceptible to a variety of pests and diseases. Insects and fungal infections are common issues and environmental issues such as droughts, flooding, and poor soil increases the likelihood of infestation or infection.

The prevalence of diseases can be reduced by only watering around the base of the tree and by avoiding wetting the leaves and canopy of the tree. Localized humidity can be decreased by limiting the amount of nearby plants such as grasses, shrubs, and nearby trees. Good air circulation will help dry the ambient air as well.

III. Uses and Benefits

• Uses

The kernels are often eaten whole, either fresh or roasted and salted, and are also used in pistachio ice cream, traditional Persian ice cream, kulfi, spumoni, pistachio butter, pistachio paste, and confections such as baklava, pistachio chocolate, pistachio halva, pistachio lokum or biscotti, and cold cuts such as mortadella. Americans make pistachio salad, which includes fresh pistachios or pistachio pudding, whipped cream, and canned fruit. Indian cooking uses pounded pistachios with grilled meats, and in pilao rice dishes.

The shell of the pistachio is naturally a beige color, but it may be dyed red or green in commercial pistachios. Originally, dye was applied to hide stains on the shells caused when the nuts were picked by hand. In the 21st century, most pistachios are harvested by machine and the shells remain unstained.

• Research and health effects

In July 2003, the United States Food and Drug Administration approved the first qualified health claim specific to consumption of seeds (including pistachios) to lower the risk of heart disease: “Scientific evidence suggests but does not prove that eating 1.5 ounces (42.5 g) per day of most nuts, such as pistachios, as part of a diet low in saturated fat and cholesterol may reduce the risk of heart disease”. Although a typical serving of pistachios supplies substantial food energy (nutrition table), their consumption in normal amounts is not associated with weight gain or obesity.

One review found that pistachio consumption lowered blood pressure in persons without diabetes mellitus. A 2021 review found that pistachio consumption for three months or less significantly reduced triglyceride levels.

IV. Harvesting and Storage

If you are planting a pistachio tree, you are in for a rather long wait. From the first harvest after five to seven years, it can easily take another decade before the tree reaches maximum fruiting.

In October, when pistachios are ready for harvesting, the hulls will turn a beautiful pink-yellow color and the epicarp (the outer husk of the nut) will separate from the inner husk. Once this occurs, simply rap the branches to dislodge the pistachios.

For an easy harvest, try placing a sheet or tarp or sheet below the tree before dislodging the fruit.

After harvesting, be sure to remove the epicarps within 24 hours for the best flavor and freshness.