What’s native to sand dune “soils”, hardy to Zone 4 for sure, possibly to Zone 2, handles blastingly hot summers, and smells like chocolate? Blowout penstemon (Penstemon haydenii).
While I’ve known the largely North American penstemon group most of my life, most of them are slender stalked, grass-y looking plants with small, delicate-ly colored trumpet shaped flowers that ride like flags up the stem/ mast. The occasional aberrant penstemon with vivid colors is known, but none of them, pastel or not, have ever smelled like anything in particular to me.
None of those descriptions work for blowout penstemon, except maybe the delicately colored part. Blowout penstemon is built of a fat stack of leaves and stalk, with hale flowers robustly anchored in, the better to withstand the constant winds of its native Nebraska Sandhills.
The flowers bloom in late spring. They are a subdued lavender pink trumpet and when I lean in close, they smell like nothing so much as flowers and chocolate. This is one of the single best smelling flowers I’ve met.
Where would one get something like these for their rock garden? Only with much research, some good connections, and a hardy dose of luck. Blowout penstemon is on the Federal endangered plant species list and known to grow in the wild in only 6 counties.
It’s not on the mass market (yet), but its rarity means that if somebody did figure out how to improve the germination and transplantation rates (both low), they wouldn’t have to do all that cross-breeding mucking about that is usually “required” to get a flowering plant from the roadside ditch to the retail nursery. (Yellow flowered black locust trees? Good grief.)
Will we see it soon? Ask the horticulture departments of the prairie state universities. They are the only ones I know with permits to collect seeds and to distribute the resulting plants, but wow do they need the money a marketable, drought tolerant, rock garden flower would bring.