Pacific Northwest Gardening: Plant Doctor, 1 by bonehead

bonehead wrote:
My paprika yarrow was very sparse this year. Not as thick and not as tall. No particular bugs or disease that I can see. I wonder if it is one of those plants that 'loses vigor' after a couple years. It was planted in 06. I've been reluctant to plant yarrow in general because I find it weedy and am not taken with the more common varieties, but the vibrant color of this one convinced me otherwise, and up to this year it has really held its own with the weeds. Any ideas? Here's a pic of it from last year, it really is pretty, but even the flower heads this year are skimpy.