Pistachios come from the Pistacia vera tree. The edible pistachio is the seed of a fruit produced by this tree, which has been cultivated for thousands of years, primarily in the Middle East and Central Asia. Today, major commercial production occurs in regions like the United States, Iran, and Turkey, all of which provide the unique climate the tree requires.
The Pistachio Tree
The pistachio tree (Pistacia vera) is a slow-growing, deciduous member of the cashew family (Anacardiaceae). It typically reaches 20 to 33 feet in height and is known for its remarkable longevity, with some specimens capable of living for over 300 years. The tree is adapted to harsh, arid climates, requiring long, hot summers for proper fruit ripening and a distinct period of cold dormancy during the winter.
The pistachio is dioecious, meaning the male and female flowers grow on separate trees. The male trees produce pollen, which is then carried by the wind—a process called anemophilous pollination—to fertilize the flowers on the female trees. Growers must strategically plant approximately one male tree for every eight to twelve female trees to ensure adequate pollination. Only the female trees produce the fruit that contains the edible seed.
How the Nut Develops
Botanically, the pistachio is not a true nut but is classified as a drupe, which is a fleshy fruit with a hard, stony shell surrounding the seed. Similar to a peach or an olive, the pistachio fruit has three distinct layers: the outer hull, the hard shell, and the edible kernel. The outer layer is the hull, which is initially green and turns a rosy red color as the fruit ripens.
The hard, pale shell is the endocarp, which encases the light-green kernel, the part of the fruit that is consumed. A highly desirable trait is the natural splitting of the shell, a phenomenon known as dehiscence, which occurs while the fruit is still on the tree. This natural split happens because the expanding kernel exerts pressure on the shell, causing it to crack along a predetermined suture line. The timing of this splitting is a crucial indicator of maturity and is closely monitored by growers.
Cultivation and Harvest
Pistachio cultivation is a long-term investment, as the trees have an extended juvenile period before they become commercially productive. A newly planted tree can take five to eight years to begin bearing a minimal harvest, and it may take 15 to 20 years for a tree to reach its peak production capacity. Once mature, the trees have a tendency toward alternate bearing, producing a significantly heavier crop one year followed by a lighter crop the next.
The harvest takes place in late summer or early fall, typically from late August through September, when the hull loosens and the maximum number of shells have naturally split. Modern commercial harvesting relies on specialized mechanical shakers that grasp the trunk and gently vibrate the tree. The ripe fruit then falls into large catching frames, ensuring the nuts never touch the ground. Preventing ground contact reduces the risk of contamination from soil microorganisms. Immediately after harvest, the outer hull must be removed and the nuts dried quickly to prevent staining of the shell and maintain the quality of the kernel.