I eventually got several plants from Harlan, and here are the two that I've grown for years in my home garden. I need more. They have put up with a great deal of abuse (I've sprayed the grass growing with them with weedkiller for instance) and carried on: unlike other dayflowers, these will not spread all over your garden and become a menace. They are demure and comely, covered with silken hair when they emerge, and blooming for weeks on end in early summer. Who could ask for anything more? (Far more deserving of the GCA Freeman medal than the recently awarded Spigelia marilandica, which is a fussy woodlander for humid, mild microclimates).
I shouldn't be telling you about this, since I have decided come hell or high water I'm going to order a whole flat of them next spring (they are incredibly inexpensive) and plant them everywhere in my garden. Bluebird has been selling these for years, but I have yet to see them in a garden center, or in another garden (aside from Dyck and a few not too happy tufts I planted at DBG) for that matter. Bet you don't have it!
It is truly strange to me that this, one of America's most glorious native wildflowers, can languish (as it were) while the unwashed masses positively gush over all manner of technological devices, media nonsense, SPORTS (for Heaven's sake) and the usual glut of consumer crap that clutters the airwaves and mucks up our otherwise meaningful lives. I betcha Brangelina has significantly more Google hits than tharpii. Helllooooow? Perhaps that's why we are so cheerfully going to hell in a handbasket?