Pistachio trees grow best in desert like climates – with hot days and cool nights. Most suitable is a height of 150 − 250 m above sea level. The trees are very tolerant towards alkali and salt. The wild growing pistachio tree has only very small pistachios. Only by the so called grafting its nuts get bigger and the number increases very much. In agriculture the grafting method has been known for centuries. It means artificial implantation of a twig of another variety into the tree. This method is also much used in the local fruit orchards. Pistachios grow in heavy grape-like clusters, and like almonds, are surrounded by a fleshy hull. Pistachios ripen in late summer or early autumn, their hulls becoming rosy and their inner shells splitting naturally along their sutures.
Pistachio orchards can successfully bear nuts for centuries in what are known as “alternate-bearing” cycles, i.e., their crop yield is heavy one year and light the next. Unlike almonds, pistachios produce male and female flowers on separate trees. Thus, in order for pollination to take place, both male and female trees must be present, or alternately, branches from male trees must be grafted onto their female counterparts. It requires wind—not bees—to carry pollen from male to female flowers. Therefore they are not frequented by bees or other insects. The pollination starts regularly during mid March and is finished at the beginning of April. During the next four weeks it is very important for the development of the pistachios that the temperature does not drop below 0° C. Frost, which can still occur in the growing areas until middle of May, destroys the young fruit and can devastate total crops.
The world´s biggest growing areas of pistachios are in Iran, around the cities of Kerman and Rafsanjan. The second largest are in the Joaquin valley of South California. As the pistachios are very much in demand worldwide, all plantations in all other parts of the world are constantly enlarged.
At harvest time, pistachios are knocked onto a catching frame, never allowing them to touch the ground. From there the nuts are loaded onto containers and rushed to the processing plant. Pistachio nuts must be hulled and dried immediately to preserve their delicate quality and to prevent their shells from staining.