Rhododendron viriosum hybrids

Rhododendron ‘Festive Bells’ is currently flowering in my shade house, so this seems like a good time for a quick post on Rhododendron viriosum hybrids.

R. viriosum is a vireya, a tropical rhododendron, and is one of only two Rhododendron species native to Australia. It has red, bell shaped flowers and is noted for its phenotypic dominance and the vigor that it imparts to hybrids. Hybrids with R. viriosum as a parent almost invariably have bell shaped flowers in some shade of red, and they are usually strong growers. Appropriately, the species name virosum is derived from the same root as the English word “virile”. The species is difficult to locate in the United States, but I am currently growing two first-generation hybrids and have previously grown a third.

Rhododendron ‘Festive Bells’, shown above, is my favorite of the three. My plant, purchased a year ago, is currently blooming for the first time, and the flowers are absolutely amazing. They are some of the best flowers that I have ever seen on a rhododendron, and perhaps on any plant. The color is a pure, intense fire engine red and the flowers have an incredible waxy texture that makes them look as though they are made of plastic. Like many vireyas, R. ‘Festive Bells’ is somewhat lanky with long internodes, but flowers are nicely in-proportion with the plant size. R. ‘Festive Bells’ has R. viriosum as the seed parent, but the pollen parent is unknown.

Bovees V97 is an unregistered clone of R. viriosum x R. christianae bred by E. White Smith, former owner the Bovees Nursery in Portland, Oregon. Bovees was for many years the preeminent source of vireya plants in the United States. It closed a few years ago, so I was happy to find this hybrid still offered for sale by Pacific Island Nursery in Hawaii. Genes from R. christianae have imparted orange tones and a more horizontal stance to the flowers, but the plant still has the vigor expected of an R. viriosum hybrid.

Rhododendron ‘Little Maria’ was a beautiful little plant that grew in my collection for about five years. The cross is R. viriosum x (viriosum x gracilentum). R. gracilentum is a miniature, cool-growing species from the mountains of New Guinea at altitudes of 2000-2745 m above sea level [1]. Despite the double dose of R. viriosum in the ancestry of R. ‘Little Maria’, R. gracilentum is dominant for plant size. A large specimen of ‘Little Maria’ can fit in a 4″ pot, and both leaves and flowers are about half the size of those of R. ‘Festive Bells’ or V97. Unfortunately, R. gracilentum also seems to be dominant for heat tolerance (or lack thereof). Plants purchased from Bovees died very quickly, but I had better luck with cuttings that I rooted in North Carolina. Anecdotally, I have noticed similar results with other vireyas. When vireya plants in my collection die, it often seems to be because the root system has failed catastrophically in the heat. For some reason, roots that have grown in North Carolina seem tougher–perhaps they have different fungal symbiotes or are better adapted to my potting mix.

Eventually, all of my Rhododendron ‘Little Maria’ cuttings died in the summer heat, and I have been unable to replace them. I am hopeful that V97 will do better in our climate, because R. christianae is from more moderate altitudes of 600-1525 m [1]. Since the other parent of ‘Festive Bells’ is unknown, I will just have to hope for the best, but I have already rooted a cutting as insurance.

Reference

1. Argent, G. (2015) Rhododendrons of subgenus Vireya, 2nd edition. Royal Botanic Garden, Edinburgh.