There could be a sport or a microclimate that makes the rhodies do that. Rhodies in a drought area, for example, can rebloom when they get heavy rains for example. In rhodies, this Fall Flush can occur at the expense of the Spring Flush (making the Spring Flush smaller than what it should be). If the owner will let you get some cuttings, see how they behave in your garden.

Our County of York rebloomed to a small degree this past fall, after all the rain we had here all year last year. (It was ideal weather all last year here for the rhodies!) But the leaves on County of York are giants and very distinctive, so it couldn't be that one, and I think it's old enough that it's not particularly likely to ever do that again unless the weather is unusually wet again all year long. Catawbiense Album would be a variety that might well be widely sold around there because of its hardiness. Ours has never bloomed in the fall, though it's only 10-15 years old and perhaps less mature than might be required for reblooming to be expressed.

Where you are, perhaps the nearness to the building and perhaps also a nearby pavement that helps to hold heat is making for a warmer microclimate in that particular spot than what you might ordinarily figure for the wider area? Still, it doesn't seem especially likely that whoever chose the variety to go there would have had Loder's White available from a local nursery, since it is ordinarily rated only for hardiness down to 0 degrees. But perhaps the building's owner is a rhododendron aficionado ordering rodies from farther south, or something unusual like that? Anyway, of the rhododendrons that we have, Loder's White seems something of a possibility.

Our Loder's White didn't rebloom the first 8 or 10 years we had it, but it has rebloomed reliably for the past 25 years or so. The first time it did that, it was just a single fall bloom. In subsequent years the fall bloom got to be a few more trusses and has gradually increased a small amount, to the point of being noticeable without looking for the blooms, though by no means is the fall blooming remotely close to what the plant does in the spring. The trusses tend also to be smaller, with fewer flowers in each truss in the fall than in the spring. They bloom not long before our first frost.

The plant is in a spot that is difficult for me to reach, or I think I'd have tagged some of the fall blooming terminals to be able to say for sure that it sets more buds on a terminal after the fall bloom on that terminal. I know it seems unlikely, but looking at the plant in the spring, I can't find any obvious places where there are missing blooms that already got spent in the fall; the whole plant is ablaze in fragrant white trusses. Last spring I specifically looked for terminals that had no blooms and couldn't see any from a few feet away.

A distingishing characteristic: any single truss isn't heavily fragrant on Loder's White, but the fragrance is there, and the fragrance from the plant as a whole wafts so that you don't have to get close to it to smell it.

I've spent years trying to keep track of weather conditions so as to figure out what is causing the rebloom in the Loder's White. But it does rebloom every year, no matter what, with or during a drought, or frequent heavy rains, very hot summers, or very cool summers, or widely variable summers. I'm convinced that the determining factors are the genetics of that plant and its degree of maturity. I suppose if we didn't water at all during a drought, that might set it back enough to cause it to skip blooming entirely, but we're not trying that with any of our rhododendrons.

One other thing that's interesting or different about this rhododendron: it might have a tendency to sport. Ours sported during a single year when it was about 10 or 15 years old. A single bloom that was lavender. I meant to tag it but thought that I could always do that the following year. Well, that terminal, whichever one it was, reverted back to white after that one sporting year and has remained white ever since. So perhaps this fall-blooming thing is something expressing some unusual genetics that is a cousin to a sporting tendency?

Anyway, I don't know that all Loder's Whites rebloom, or even that any others do, but ours certainly does. And it's a highly desirable characteristic, coming with no dimunition of the spring flush.

I've thought about this tendency to rebloom some, and compared it with the development for roses. Roses in Europe a couple of centuries ago were single flush roses. But European breeders found a few Asian varieties that rebloomed, and they used them in a breeding program aiming for reblooming characteristics. It would be a good thing if the same kind of development could come along for rhododendrons. If a breeder wanted his/her new rhododendrons to head in a reblooming direction, then using Loder's White might be one to look at, or at least to look at its parentage for some reblooming genes.

Regarding the hardiness rating on Loder's White... Some of that might vary according to surrounding conditions. Ours survived at least one night down to -3 degrees (probably more than one) and one night down to -6 in the coldest winter ever here in the 1980's. That was an extended very cold period when the daytime highs didn't get above freezing for ten days. It was cold, and stayed cold, and Loder's White did fine. I don't know that it would have done as well if it had gone from 60 degrees during the day to -6 degrees at night, but anyway, given real weather conditions here on its east-facing section of the slope on our berm, Loder's White seems pretty hardy to me.

Since there aren't many rhododendrons with fragrance, if you smell a fragrance when the rhodies bloom at the building next door this spring, Babs, it might very well be Loder's White. But if you don't smell anything, that doesn't conclusively mean that it's not Loders' White, either; the sense of smell is so variable among different people.

Whatever it is, I hope you can get cuttings! Just in case it's a sporting situation, you might memorize some of the terminals when and where you see the fall blooms this coming fall, and then be sure to take some cuttings from those terminals and label them differently. I wonder whether breeders (like Greer Gardens and Van Veen's in Oregon, for instance) might not be interested in having some of what you have if you succeed?

Best wishes,
Mary

Thanks for the responses. The plant is against an east wall of a relatively new (maybe 6 years old) dorm on the U of NH campus, so I don't imagine it's anything incredibly rare - they seem to get plants from wholesale nurseries. In general plants seem to be hardy to zone 5 as far as I can tell. I'll have to see if there is scent in the next few weeks and check out some images of Loder's White to see if it might be that.