Mine are doing the same thing. I think it might be because they need to be split apart every 3 years or so. In your case, check that the amount of available light, etc. hasn't changed (because of growing trees or new buildings next door, etc.). I think I'll have to divide some of my primroses this summer for the same reason. It's only the older clumps that seem to be petering out.

Good luck with them!!

-Gord

I DIVIDED THEM LAST FALL AND THEY HAVE LOTS OF SUN, SO IT MUST BE SOMETHING ELSE...