Pistachio Pistacia vera L. Anacardiaceae

Species description Pistachio trees are medium sized deciduous trees pinnate oblong, pale to bright green leaves. The tree produces its nut-bearing branchlets on one-year old wood. Pistachio flowers are dioecious— individual flowers are either male or female, but only one sex is to be found on a tree. The fruit is technically a drupe fruit, containing one elongated seed. Splitting of the seed coat (hard outer shell) begins a month before fruit maturity, usually in July, and extends until September. The interior seed is pale green with a distinctive flavor.

Natural and cultural history Pistachios are native to western Asia, Asia Minor and North Africa, and they have a long history of human distribution across the Old World. Wild populations of pistachios can be found in the desert regions of Lebanon, Palestine, Syria, Iran, Iraq, and India.

Planting considerations and propagation techniques Pistachio trees can reach 20 feet in height with a canopy diameter of 15 feet. They take up to ten years to reach fruit-bearing age, though they can live for 150 or more years. Long, hot, dry summers and moderately cool or cold winters with low humidity characterize the native range of pistachios, and the tree produce best with 1,000 chill hours. Young trees however, are sensitive to freezing temperatures, and late spring frosts can kill flowers. Cold hardiness ranges from 5ºF-15ºF, though reportedly down to 0ºF in Iran. In Arizona, they should be planted below 4,500 feet in elevation. Since, pistachio trees are dioecious, both male and female plants must be grown for pollination; the trees are not self-fertile. Pistachio flowers are wind pollinated, and winds that are too strong in spring may interfere with pollination and reduce crop set. A few male trees are generally interspersed with female trees in commercial orchards. In backyards, at least one male and female tree must be planted. The trees tend to be alternate bearing as they age. Pistachio trees thrive in deep, well-drained sandy loam soils, though they will grow in rocky, shallow soils. They tolerate saline or alkaline soils and those with high lime content. Pistachios are propagated by T-budding and occasionally by grafting. The rootstocks may be grown from seed of three different wild pistachio relatives, including include Pistacia atlantica, P. integerrima, and P. terebinthus. These are grown in nursery pots before grafting, and typically not bare rooted during planting as the roots are highly sensitive to drying.

Water needs Pistachios are drought adapted, but irrigation can improve nut production. The young trees are sensitive to drying and should be irrigated regularly.

Care Trees should be trained during the dormant season to a central leader with 2-5 scaffold limbs branching about 4 feet above the ground. After the initial training, little pruning is needed except to thin branches. Heavy pruning will reduce nut yield.

Harvesting and processing Pistachio nuts mature in early fall, and the clusters may be easily harvested by shaking the branches or knocking them with a pole. Pistachios are consumed fresh, dried and dry-roasted; they can be used with meat dishes and in ice cream, sweets, and candies.

References and resources California Rare Fruit Growers (CRFG). Pistacia vera L. http://www.crfg.org/pubs/ff/pistachio.html. Ferguson, L. 2008. Pistacia vera, pistachio, pp. 20-26. Eds. Janick, J. and R.E. Paull. The Encyclopedia of Fruit and Nuts. CABI Publishing, Cambridge, MA. Plants for a Future (PFAF). Pistacia vera – L. http://www.pfaf.org/user/Plant.aspx?LatinName=Pistacia+vera. Tous, J. and L. Ferguson. 1996. Mediterranean fruits. p. 416-430. In: J. Janick (ed.), Progress in New Crops. ASHS Press, Arlington, VA.

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