It does make quite a nice dyeplant - yellow, of course - but it doesn't hold it's dye well when dried. I picked bunches one year and hung them to dry. While the shed smelt fabulous, the flower heads turned to seeds and the dye didn't happen.
Neither have I had much luck with commercial herbstuffs. What I got appeared to be almost all leaf and despite my best efforts, only produced a pale yellowy green. Quite pretty, but not really what I was after.
I have wool, cotton and random mixed yarns skeined and mordanted and this time, I'll see what can be done with the fresh flowers!