Wait a minute I just answered your other question where you state that the peony is in the ground. So is this a different tree peony?

Having read your first question and now this one. and reading between the lines, do I understand these are plants you have propagated from seed from the yellow mother? How long have they been in pots? have you ever potted them up? re-freshed the compost at the top,
Kept them out of the morning sun?
Some people keep tree peonys in pots but they are generally large pots. Plant some out in the ground and it might make the difference.
Some varieties of tree peonys wont flower until they are mature specimins, 5 - 7 years old.

check out the link below by cut and paste, to help you with your questions.

http://www.treepeonygarden.com/english/plotting/plot-eng.htm