Pistachios are a relatively recent arrival to California.  Unlike their nutty cousins Almond and Walnut, which have been grown in our state for centuries, the first pistachios were planted just over 50 years ago.  Our little orchard was one of those, as was the orchard just across the street at the UC Davis Wolfskill Experimental station.
Originally from Persia — modern day Iran — pistachios might be better adapted to the hot, dry summers here than either of their “cousins”.  They can survive on less water and tolerate poorer soils.  And unlike almonds, they are generally still dormant during our rainy season here, which means they have fewer fungal diseases and pollination problems resulting from wet weather.
Nonetheless, they are a frustrating crop to grow.  The biggest issue is their strong tendency to “alternate bear”.  They have a heavy crop one year, followed by a light crop the next.  And they take longer to start producing nuts than either almonds or walnuts — fully eight years.  These two factors have historically made them a less popular choice for farmers despite their other advantages.  Just imagine starting a job, then having to wait 8 years for your first paycheck.  Then the next year, your paycheck gets cut in half.
Despite those issues, farmers in California have planted millions of pistachio trees in the last ten years.  Several factors are involved.  First is the embargo on Iranian products, including pistachios — they remain the world’s largest grower.  Second is the skyrocketing popularity of nuts in general and pistachios in particular.   Third is the drought-tolerance of this particular nut, which is especially appealing to growers in areas without abundant winter rains.
But climate change might throw a giant wrench into the plans of pistachio growers in California.  Until just a few years ago, almost everyone assumed that the trees would adapt quite well to a warming world, given that they have better heat and drought tolerance than both almonds and walnuts.  Planting them was almost seen as a way to hedge against climate change.
Then, in 2015, almost every orchard in the state failed to produce a crop.  After almost a year, researchers identified the problem — the warm winter that had failed to deliver the “chilling hours” that pistachios need.  All tree crops grown in California need a certain number of hours below 45 degrees to set fruit or nuts.  But it turns out that pistachios need more than just about any other crop.
In the Central Valley, winters have actually been warming more than summers.  The “Tule Fog” that used to shroud the valley in cold, damp weather for months has almost completely disappeared.  The nights have actually gotten colder, but the days are warmer and sunnier.  The daily temperature fluctuation confuses the trees into believing that spring has arrived and breaking their winter slumber which is so important for producing the crop.
Tree breeders are now frantically working on new varieties that will require fewer chilling hours.  But that won’t help farmers who have already sunk thousands of dollars per acre into their existing orchards — some of which are just now starting to bear fruit.
We “inherited” our pistachio orchard, and have had a love-hate relationship with it over the years.  It will often go two years without hardly producing any nuts — this year and last year, for example. But then, just around the time we begin discussing removing the trees, it produces a limb-buster of a bumper crop.  All is forgiven and the orchard gets another chance, only to disappoint us again the following year.
Until we cut those trees down, we will continue to put the occasional bag of delicious green and pink nuts in your boxes.  Enjoy.