Penstemon fasciculatus environment?

All that's said about it in Bob Nold's Penstemons is that it is native to limestone areas in southwestern Chihuahua.

Here are some accounts from the U. of Arizona Herbarium; the full descriptions can be downloaded if you have spreadsheet software (e.g. Excel) on your computer:
http://loco.biosci.arizona.edu/herbarium/db/get_specimens.php?taxon=Pens...

In case you don't have Excel, though, here are the details:

Well, I guess that gives some idea of elevation, and range of habitat, and suggests that it is not particular to limestone, if it also grows on acidic rocks (rhyolite).  There doesn't seem to be too much information available about it, overall...

If these are the Plant Select penstemons, I believe these are offsprings of Meyers's hybrid 'Mexicana' (though the trade seems to insist on saying it's 'Mexicali', which it ain't), P. palmeri x P. parryi x a hybrid in Section Fasciculus.
Like most "monsoonal obligates" they prefer considerable moisture after mid summer. As garden plants they are probably more successful than most species of penstemon in the long run.

These plants are from seed collected by Mike Kintgen. They seem happy in their temporary home. I'll move them to a new location next spring where the red flowers will show up well.

Oh. Well, the same thing applies, since flowering is triggered by moisture; in this case, by the Mexican monsoon. Chihuahua has a monsoonal flora, as does New Mexico and Arizona (Colorado does not). In Denver, some of the "monsoonal obligates" respond to spring moisture and then stop flowering by mid summer. Some plants eventually just give up and die, unless they're irrigated. 
Early 19th century penstemon breeding was done with Mexican species (with the moisture-loving P. cobaea thrown in for flower size) in England and France because of the willingness to flower in summer-wet climates.