Posted: 28/09/2014 at 09:26
I'd cut them down when all the flowers have finished. They'll grow back to the same height, or even taller, next spring/summer.
As the seed pods dry and begin to open you could save some to sow next spring - although you'll probably find lots of little self-sown ones popping up in the spring anyway.
As for the one you want to move, I think I'd move it just as it starts into growth in the spring.