I just cut the old stalks off of mine. I didn't want seeds and only the leaves help the plant get ready for next year.

I remove the whole of the flowered stem on mine as soon as the flowers fade rather than deadheading - I don't want the plant to put energy into producing seeds which I'm never going to do anything with... but some people do collect the seed, in which case, you'd need to leave them alone. Although once you've collected the seed, not much point in leaving the stems in situ...

Thanks for the info, I have now cut them all off :o))