I have had many many years that ITOHs didn't bloom. I kept thinking, did I plant this too shallow, too deep, what on earth am I doing wrong? I grow all sorts of peonies here, that, for the most part do well.
This year I had every one bloom. My thoughts are a couple:
one, the weather was cooperative or it seemed to be the later cold temps in the spring were not cold enough to damage buds in development.
two I redid a huge area where they reside, adding a fertilizer and blend of sorts to my soil. Everything I planted with this mix is planted near the ITOHs. I think they too benefited from the fertilizer soil blend.
Just a couple thoughts on the subject. Hope it helps. Here I am anxious to see if everything carries over to next year.I'm hoping.