Allusion to Meadowlark Botanical Gardens implies you are in the DC area.
Along the east coast that is the transition zone where it starts to become uncommon to see elepidote rhododendrons (e.g., the typical kind with bigger leafs. Lepidotes have smaller scaly leaves and barring a few exceptions like R. minus, 'Chapmanii Wonder' or PJM, are even more cranky) I knew a DC area landscaper 15 years ago who refused to plant them even when clients asked. Unless ideally *sited, planted, and cared for*...root rot will eventually claim them. OTOH drive north 3 hours and on the Pennsylvania Main Line you will a rhododendron in every single garden. Drive 3 hours south or SE and you will not see a single one in hours upon hours of driving.
From DC this line extends SW along clines of increasing elevation. I recently saw some "American ironclads" like English Roseum, as I drove up in elevation from Spartansburg, SC (850 ft) to Bostic, NC (1200 ft. where I was visiting, but that was in a valley). Although they were still very uncommon. The mountains start to have native Catawba rhododendrons, of course, and that might be what I was seeing. The ironclads are genetically speaking, mostly Catawba rhododendron. I have seen pictures of a quite rot resistant 'Bibiani' that was growing in a zone 7b display nursery/garden center outside Atlanta, but the details beyond that have washed from my mind. That would have been at the limits of its hardiness...I wouldn't try that one in the DC area. What I would try: if you want to guarantee success in DC, grow one the cultivars bred for root rot resistance, like the "Southgates" promoted by Southern Living, or the related hybrids created by Thornton like 'Opal Thornton'. What's left of Rarefind might offer those this spring...who knows. I don't get the sense the Southgates really took off in the south. But they will do just fine in low to mid elevation MD/VA, and of course DC and DE. They are crosses of the old ironclads that incorporate a more recently discovered Taiwanese species, R. hyperythrum, that imparts incredible vigor and rot root resistance.
https://www.woodlanders.net/in...
BTW, be warned that garden centers throughout the DC area are happy to sell typical cultivars, including some very rot prone ones like 'Capistrano' (known to the founder of Rarefind as 'Crapistrano') because they are loaded full of anti-fungals by the wholesalers and are therefore going to die after the 1 year guarantee period is over! American capitalism at its finest, right?
