John A. Clement, Granby, Massachusetts
Having lived in New York City for fifteen years, without even a house plant, much less a garden, I've had to adopt some unorthodox devices to satisfy my passion for rhododendrons. Lacking real rhododendrons, I've indulged myself with imaginary ones. Books have helped - Leach, Davidian, Cox, Galle, Cullen & Chamberlain have all passed through my hands.
The result of all this is my pastime of armchair hybridizing. I've amused myself by dreaming up unusual crosses that the professional hybridizers seem to have overlooked. This method certainly has its advantages - no tricky seedlings to tend, no agonizing disappointments after ten years of waiting, no hybrid sterility or apomixis. The best advantage is the opportunity to make an unlimited number of crosses. Not even a Lord Rothschild in his prime can make more crosses in the field than an armchair hybridizer can make in his head. Here are a few of my favorites:
A cross similar to this one ( arboreum x catawbiense ) was the basis of the hardy ironclads, arboreum providing the color, catawbiense the hardiness. Simiarum is very heat-tolerant and could form the foundation of a similar race of rhododendrons for the South. Because simiarum is a better rhododendron than catawbiense (a high-class white rather than a second-class lavender), this new race might be more impressive than the present ironclads. 'Loder's White' in Florida, 'Mrs. Furnival' in New Orleans, 'Jean Marie de Montague' in Houston - that's the sort of thing I have in mind.
The large-leaved Himalayan giants seem, to have been bred only among themselves, resulting in progeny as gorgeous and un-adaptable as Odontoglossum orchids. They refuse to grow anywhere but fog pockets in Oregon or Scotland. Maximum , with its own relatively large leaves, would inject a dose of hardiness and adaptability into this feeble strain. The first generation would probably be unimpressive, but crossings and recrossings might yield a hardy plant with a good portion of the wonderful leaf quality of sinogrande .
These are both large species and the offspring would be a tree. That's what I have in mind: a small tree trained to a single trunk, with scarlet flowers. As far as I know, there is no tree now known to temperate horticulture with pure bright red flowers, and I imagine that adventurous gardeners would welcome such an animal with alacrity. As prunifolium is one of the latest bloomers and arboreum one of the earliest, there's no telling at what season this novelty would bloom. It must be admitted it wouldn't be very hardy: probably limited to the Camellia Belt. Arboreum x calendulaceum would yield a hardier variant, though probably less tree-like (provided of course that the tricky 5-chromosome calendulaceum would deign to mate at all with arboreum .)
'Loderi King George' x 'Daviesi'
If you think not in terms of "rhododendron" or "azalea" but in terms of "shrub", this cross might be interesting. An azaleodendron - I'm not sure whether it would be evergreen, deciduous, or in-between. It would almost certainly be big, in the class of a hydrangea or smoke bush.
In my mind's eye I see the flowers as a foaming, cascading, delirious profusion of highly-scented snow. It would probably be hardy and adaptable in much of the East, at any rate much more so than Loderi. A similar but more heat-tolerant cross would be fortunei x serrulatum.
Yes, this is "impossible:" lepidotes don't cross with elepidotes. Nevertheless it happened once. Griersonianum and dalhousiae , like Pasiphae and the bull, combined in unnatural marriage to produce the minotaurian 'Grierdal'. My philosophy is that if it happened once it can happen again. (After all, the rose breeder Pernet-Ducher made thousands of crosses before succeeding in obtaining hybrids of the Persian yellow rose.) Perhaps rhododendron breeders haven't been diligent enough. I choose this cross as my example because if we're going to attempt the impossible, we might as well go the whole hog: griffithianum and nuttallii would yield the biggest, most ostentatious flowers in the genus. As Mae West said, "Too much of a good thing is wonderful".