I think to even consider this question you should provide more details like: –what zone are you in? –what kind of light conditions are you in? –what kind of soil do you have? –how has the leaf growth been?
But more important, have you ever done a soil test? I had a shrub that I was having a lot of trouble with and bought not only a pH test but also one to test the levels of Nitrogen, Potassium and Phosphorous. These kinds of kits are readily available in most garden supply stores and very useful! For example, the azalea I had that wasn’t blooming was in soil that not only had the wrong pH but also very very depleted in Nitrogen. I ended up moving it [since it was also getting too much sun] but since yours are probably where you want them and nicely established, you can always supplement the soil depending on what the kit tells you. Ultimately if your plant isn’t getting enough nutrients, it just won’t have enough energy to produce flowers.