I have found heavy pruning makes mine flower, you won't kill it, trust me.. if it feels threatened, it will flower, as strange as it may sound... Like Brin said, if its feels all comfy with food and water, it won't propagate.. I had a hard time wrapping my head around it, (its a plant), but saw a difference when I pruned it back 50% or better in the winter..
I also found it strange that I have two that flower in the spring, and six that flower mid to late summer.. The spring ones are the ones I have to prune back and just did it today as a matter of fact.