I'm wondering if they even respond well to being transplanted. I have two that I moved from smaller containers into wine barrels. After a couple months or so, I don't detect any spreading of roots into the new soil. I think they got root bound and I didn't disturb the exterior enough when moving them. They are still alive though and one in particular is producing well.
What kind of soil mix do you have in the barrels? Blueberry shrubs must be planted in acidic soil or potting soil.