I personally don't deadhead mine *or her's* until
fall time...I tend to let mine just be on a regular schedule... no double blooms...
Only because I live here in zone
5 and it's a short enough season, that by the time they bloom,
stay blooming for a week or more, and then start to die down, it's almost the end of the season...
and if I cut it down to promote a second growth and flowering, I run the risk of the plant
having new green~tender growth, late in the season,
when I really want it to be preparing it's self for nightie~night here for the winter...
To me, it weakens an already not allllllllll that
hardy type of a plant
...I mean it does good, under the right conditions, and then sometimes can fade..I've had gorgeous one's and then they've died or didn't come up the following spring
so, like I said for me, I just leave it....
But.....someone in a longer growing
may very well be able to do this, the double flowering and have it fair well.
I know they re~seed
on their own too, my mom
had one do that... *I never did*