The only real good long term solution is drainage. I have a lot of fruit trees. Not as many as TJ, of course.

I planted six trees, apples, pears and cherries in a poorly drained portion of my property. All died eventually. Some lived for as long as six years but in the end they couldn't stand having their roots submerged for weeks at a time.

I think your only good, long term solution is a big French drain - maybe two.

TJ is right, that now is the time to plant. You can add gypsum to help break up the clay particles but drainage is the answer.