Question
I have 4 mature Chinese Pistachio trees (6-10 years) that never show fall colors, only green. Can you please tell me why and how I may change that so they will display fall colors  like the other Pistachio trees in my area (central California)?
Thank you very much.

Answer
Nancy;
Since my earlier message, I have had an opportunity to visit with a horticulturist colleague of mine regarding your question.  He tells me that the reason your trees are remaining green while others in your same area are showing fall colors is that probably your trees are from a different seed source.  This would mean that they are indeed not of the same genetic heritage as the trees that are changing color.

I hope this helps to shed some light on your concerns.
Regards
Steve