I don't know so much about any plant preferring to be root bound to bloom. Keep in mind that these Birds are outside, landscape plants, and when growing "naturally", they certainly can never be root-bound. That does not deter them in the least from blooming. My Birds bloomed in the spring and until mid-summer. Perhaps the oppressive heat stops that blooming. I don't know that. I would love to grow Birds again, but alas, they just get too doggone big. I have enough to do bringing in my plants during the fall/winter months as it is.