Penstemon is a perennial....it blooms and sets seeds. If you keep the seeds and dead blooms cut off it may bloom again. At any rate it will come back next year if you don't dig it out and bloom then.
Perennials usually have one bloom period a season, some will bloom a second time if you dead head it.
Linda C

Thanks for your response, Linda.
That particular perennial has been in my garden for over 10 years.
When I wrote that they 'stopped blooming little white bell flowers', I meant they NEVER have normal blooms any more.
I have many of the same variety scattered in my perennial gardens.
NONE of the plants have normal white bell looking blooms for 2 years.
The foliage is dark red/green like always.
Just NO flowers only a fuzzy wispy icky growth where you'd imagine the blooms should have been.
I should have taken a photo to show exactly what I'm seeing.
Has anyone else seen this before?

I have never seen that! Mine are about 6 years old, hope that doesn't happen to them. Maybe you could try dividing & moving them?

Do you have cottonwood trees in your area? Do you cut off the flower stems when they get fuzzy? The flower buds of this penstemon are sticky, and when the "cotton" from the cottonwoods starts flying (like it has been for a few weeks around here), it sticks to the buds and stems. They still flower, but there is a lot of cottonwood fluff on them as well. Just a thought.

When these penstemons go to seed, they get burgandy-colored teardrop shaped "pods" where the flowers were, with the seeds inside. Their seeds are not fluffy.

-Caroline