Pistachios ripen in Australia in late February/March – the rest of the world, production being in the northern hemisphere they ripen in September. In exceptionally hot summers, harvest may be earlier.
How to tell when the pistachios are ripe
The hull of the pistachio is called the epicarp. It is about 1/16 of an inch thick and adheres tightly to the hard inner shell until the nut is ripe. Take your thumb and forefinger and squeeze the nut. If the epicarp has separated from the hard inner shell, the epicarp will easily come apart and can be peeled off.
Besides the epicarp coming off easily, the color also changes. The epicarp has a reddish/yellow color during development. The color lightens in August and when ripe, it is a rosy, light yellow.
Try to time harvest when most of the nuts are ripe.
How to harvest.
The pistachios will fall off the tree when the branches are given a sharp shake. A rubber mallet hitting a branch, a fist or mechanical shaker can be used in large orchards. Put sheets or tarps under the tree to catch the nuts. You don’t want the nuts to fall in the dirt (you will lose them or the epicarp will tear).