2 different folks have asked if I know how to correct a problem with their rhodos(One is Nikko blue, I believe. The other is a small leaf version-name unsure) that stopped blooming after about 2 years. The bushes are large and in ideal locations around other healthy acid lovers. I don't think they're pruning at all. Is it normal for some species to only bloom 1-2 years? Is there a way to reactivate their blooming? Appreciate any guidance.