You say 'nowadays'. Do you mean this year, particularly, or the last few years? It may be that they aren't making good growth in the early part of the year to support flowering the following year. Try a spring prune, taking out up to a third of the older wood, starting with crossing branches, dead wood, etc.then feed and mulch. It should give the plant a 'refresh'. Phil J

I rarely get mine to flower either so I will try this Phil. I usually use fb&b. I havent tried pruning them yet.

They bloom better with extra potash. My neighbor gives his kelp meal in addition to the regular feeding. Frequent pruning to keep them in a formal shape drastically reduces bloom, too--once in spring isn't an issue, but several times over summer might be.