Rick, I had the same thing with my Pacific Giants. I ordered the New Millenium from New Zealand and they are going on several years now. They get to be about 7'. Problem is that when the wind comes up over they go. I have them fenced in but I think that binding them to tall canes would work better.
Could you tell me again how you break up hard pan clay. A friend moved out to the valley and her house is surrounded by what might as well be concrete. Cannot dig in it.