Rhododendrons: Blooming vs. non-blooming
I have two rhododendrons around my house. Both look very healthy. One is permitted to grow as tall as it can and it is almost up to the roof! It gets trimmed only very slightly. It blooms beautifully every year. The other healthy rhododendron is near a view of the back yard. Consequently, it gets trimmed every year to save the view. It never, ever blooms. I suspect this is due to the trimming. Is there a way to stimulate blooms without letting this plant grow fifteen feet tall? I might add that both of them get "pruned" by deer in the winter, but they both seem to recover quite well.
Rhododendrons in general are pruned immediately after flowering. They then use the summer to grow big buds for next year's flowers. These buds are very visible and almost look like a fat candle flame. You can easily see them by the end of summer.
When pruning, cut about 1/4 inch above a whorl of leaves (several leaves coming from one spot.)
It's possible that you are pruning too late, and thus cutting off the next year's buds. Or else the deer are doing it. If the deer are the problem, you'd expect to see few to no flowers at the bottom of the unpruned rhododendron and well as the pruned one.
If none of the above sounds possible, the non-bloomer may be a poor variety or something else is different about it from the blooming one.
Now would be a good time.
While this family of plants can take a hard prune, in general we suggest people not take off more than about a third of a shrubs growth.
If the problem was the timing of your pruning in the past, this should correct it.