Hello, for about 15 years I have been cultivating a pistachio successfully in zone 7, but in a garden in a residential area, you have to add, there the climate is a little milder than completely in the open environment. The coldest temperatures, which there were here in this time, were -17°C. There were also longer dew periods after strong frosts, or early spring break, and then again strong frosts, and even that did not harm the building. The only problem was that if during or after the flowering frosts occurred again, the fruit had set in. The tree I am talking about is a female. Three years ago I planted a male to it, because pistachio has only one of the two sexes on a plant. And exactly in the first year, the male had really formed a lot of pollen, I pollinated the female flowers with it and there was a frost afterwards and there was no fruit. There is something else to note: Depending on the variety, the male may flower either too early or too late in relation to the flowering time of the female. Too early is not so much the problem as too late, you can also shake off some pollen and keep it cool and dry, but when the male flowers too late there is logically no pollination. One idea would be to plant several males, and that the wrong time is flowering to exterminate again.