From my personal observation, I don't think 2-3 flowers will set the plants back much. Case in point is my double fernleaf. THis plant was planted in fall 2014. In spring 2015, it produced 5 buds which I allowed all of them to bloom and immediately deadheaded as soon as the petals started to wilt. I did not want the flowers to set seeds. This year, it is about the same size as the plant in 2015 but it has only 4 buds. So the flowers did set the plant back a little but not much. But you can also see that there are alot more young stems that don't end in buds coming out of the base. (Note: I did fertilize when I first planted, again the following spring, and again this spring)
2016
2015
