Perhaps your soil was TOO nice. I have had unreasonably good luck with P. smallii - I probably potted up 300 seedlings last year. Gave most of them to GNPS, but a bunch went to friends. Not as many seedlings this year, but the six plants I left in the ground were huge this spring and I cut off the seed heads on those when they were done. I left some smaller ones to go to seed.

P. digitalis has been fine also here. Got about 25 seedlings this year in various places (grows up by the mailbox and in another area too).

I got a couple of other, different penstemon this year, but so far they are still in pots. My understanding is that they are happy in drier, leaner soils. Clay doesn't seem to have been a factor as I have them in that.

The problem is that my soil gets so hard. I had smallii in a very dry between stones. It did not re-seed :(

Are you mulching?

I think I mulched that particular year with pea gravel. I put the plant on the slope by the driveway in a hot and dry rock type garden. There are still pockets of clay there, but for some reason I just can't get the soil "right" there despite years of amending. Santolina, some bulbs, lavenders, rosemary do particularly well there. The native garden had much much richer soil structure and was mulched with pine bark. They also water, where as most of my garden gets what it gets from the sky after the plants establish.

I received some Penstemon digitalis seeds in the mail, so I am sowing a few of them in a tray to see what happens. I know this is probably not the right time, so I saved some seeds for possible fall or winter sowing. I have never had any before, so I am very interested in this thread.
Susan.

Susan, if they don't germinate in two weeks, throw them in the freezer if you can for a week or two. That should get them going.