Well, there has to be a reason for all the foliage that persists after bloom time, or else why would it stick around ? Granted, the plant needs to stay healthy until it ripens it’s seeds in the fall, so perhaps that’s the main reason it hangs on. But it’s also reasonable to think that it’s building up it’s food supplies for the next spring, and I suspect that’s why most places recommend a second fertilizing after the blooms have faded. None the less, if I had to place my money, I’m thinking that the spring fertilization may be the most important one. At least that has seemed to be the outcome at my place, where up until recently I avoided spring fertilization, as a means to protect against soft growth and late frost damage. Last year I said “What the heck” and finally did some spring fertilizing, and the improvement in results was pretty noteworthy. But notably, the difference in growth the next season seemed to be effected as well. An increase in stem numbers seemed to be the outcome. Which was not always the case when I was restricting my fertilization until after bloom time. “Your results may vary” of course, but particularly for those living with naturally poor soils, doing some experimentation with fertilizing and it’s timing, is a thing worth doing I’ve found.