Pistachios and Spring Bud Break
“Pistachios need a certain amount of heat to push buds and begin flower development. Once this begins to happen, the tree is no longer in ectodormancy and the season can begin with the initiation of flowering and bloom,” said Kallsen.
“Trees and other plants, of course, are not warm blooded like us. They really dependent on the air temperature and soil temperature. So the speed at which they metabolize and the speed at which they begin plant development in the spring, depends on how warm or cold it is,” he said.
Kallsen said the amount of carbohydrates in the tree do not really trigger bloom at all.
“When it’s finally said and done carbohydrate plays a minor role in breaking endo or ectodormancy. Tree carbohydrate status does not trigger bloom (there may be some arguments on this), but I think of carbohydrates in the tree as much like the diesel fuel in the tank of a big semi-truck,” Kallsen said. “The semi is going to need that diesel once it's on the road. They cannot use it until the engine has started in much the same way that pistachio tree can't use its stored carbohydrates until spring metabolism has started.
“I compare it to the diesel engine gets started with the heat of a glow plug. Similarly, once endodormancy is broken, the pistachio tree gets started with the warmth of spring. I don't think no matter what the ratio is between sugar and starch, you're still going to need the warmth of spring to get things started,” Kallsen explained.