What coukd have happened to make them disappear after six years??

The same thing happened to my Goldstrum after a similar length of time. Not sure if it was voles or what, but one spring they were no more.

tj

Voles are a very good possibility.

And theyd leave kniophia, hyssop, baptisia baptisia, daylilies untouched?

Not necessarily :-) They have a preferred menu, I'm sure, and predation never tales place in any sort of uniform manner. It tends to be concentrated where their dens and runs are located.

There was a recent thread on baptisia and voles that might be helpful.

I'd give them a couple more weeks. I'm in SW PA 6b and it has been a cool wet cloudy spring. I've noticed everything is behind. My daffodils just finally quit blooming. I just hope it isn't one of those cold summers that everytime we turn around it is raining. The freaking furnace is still running 24/7 and sweats are still our casual attire. Ugh.

I hope they return for you but I just checked and mine are already starting. Despite abundant snow mine die back to the ground every year.

Hmmm. I'm less than optimistic they'll still show. There should be some old stalks from last year though, and if they pull up with dead roots attached it was not voles, if they pull up with no roots attached then it was likely eaten over winter.