How to Grow a Pistachio

Blog, Nuts, Trees

The Pistachio tree is subtropical and hardy. It thrives in high desert climates where the summers are long, hot, and dry, and the winters only moderately cold. This summer in California is especially hot and dry.

The pistachio most likely originated in Central Asia, and is found today throughout the Middle East, India, Pakistan, Cyprus, and Sicily. The principal producers are Iran, Turkey, and the United States. The nuts were first imported to the New World in the 1880s, but it was not until the late 1920s that the feasibility of a commercial crop was explored.

In 1929, William E. Whitehouse, an American plant scientist, spent six months traveling through Persia (now Iran). He gathered the best pistachio seeds he could find into a burlap bag and returned victorious to the high deserts of the Southwest to become the founding father of the American Pistachio industry. Of the varieties he brought back, the Kerman (so called because he found the seeds near the city famous for its carpets) was the favorite. The Kerman Pistachio has a creamy white shell with a delicate green seed.

Why then, you may ask, does much of the American crop reach the market red in color? In their natural state, of course, they are not. The practice of dyeing the shells with red food color originated in the 1800s when all pistachios were imported. Harvesting methods in the Middle East nearly always resulted in the epicarp drying out before being harvested, therefore creating oil-stained shells. These proved unattractive to the commercial market in this country, so disguising the discoloration became common. Even today, the demand for red-dyed pistachios remains strong, even though modern harvesting methods prevent shell discoloration.

To have the nut, one must first have the tree. In the case of pistachios, growing a tree 12 to 16 feet high is a challenge. It begins with seeds from selected rootstock. After the seedlings germinate, they are transplanted over a period of six to twelve months into a series of successively larger pots until they are ready for permanent planting. Finally, in a process called “budding,” a bud is grafted from a vera pistachio tree to the rootstock. Like humans, the trees are male and female, and, naturally, only the female bears fruit. It is, therefore, necessary to plant a sufficient number of male trees in each grove to assure adequate pollination. The trees pollinate in April.

Now, fast-forward six or seven years. It takes that long before a tree produces nuts in quantities sufficient for commercial purposes. The yield generally increases each year, and plateaus in about fifteen. However, the yield can vary as much as 60% to 80% in alternate years. Because pistachios have long thrived in the American Southwest, there is seldom a shortage.

Pistachio trees need a period of dormancy during the winter. If the period is too short because of a mild or brief wintertime, there will be fewer blossoms in April. There was a good bloom in the grove this year, which is the “promise” of a good crop. The trees do not need a great deal of water (being native to desert climes), but some irrigation is required to insure that they reach maturity. Our California grower is pleased with the season so far, particularly with the heat! Pistachios flourish in 105-degree temperatures, and our good-natured grower claims that he doesn’t “mind the heat.” As a New Englander, I find that hard to believe. Although we had a non-spring –cold and wet– we all wilt, hereabouts, when the thermometer hits 85 degrees!

Pistachios from a Pistachio Tree

By early June, the shell of the nut is almost fully grown. Over the next month or so, the meat begins to develop. This process is called “nut fill.” At the end of August, the nuts begin to crack open slightly, an indication that they are nearly fully ripe. Usually, sometime in September, the shakers will be moved into the grove, and the harvest will begin

If you were to wander through the grove just before harvest, you would hardly think that the trees were bearing pistachios. What you would see is a bounty of drupes–the fruit of the pistachio. The fruit is composed of a pulpy, leathery layer (epicarp) and a hard inner layer (endocarp) that holds a single seed (the nutmeat). When you eat a pistachio, you are actually enjoying the delicious green seed of an endocarp. It sounds a lot more appetizing when called a pistachio, don’t you agree?

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