Vireyas: Rhododendrons for Warmer Climates
William Moynier
Los Angeles, California

To begin with, I think a few comments regarding the title of this article are in order to avoid a possible misunderstanding. I am personally aware of a considerable number of people who are successfully growing vireya rhododendrons in quite cold climate areas, one way or another skillfully bringing them through the cold months of winter year after year. It is my hope that one or more of these people will share their experiences and techniques in a Journal article on vireyas in the not too distant future. But, since all of my experience and most of what I know about growing vireyas relates almost exclusively to our warmer climate conditions here in Southern California, this article of necessity primarily addresses the growing of vireyas under these more favored conditions.

I first heard of vireya rhododendrons in 1970. I had written to San Francisco's Strybing Arboretum for suggestions of rhododendrons which might grow in the warmer climate of Southern California. During this period I had been experimenting with a number of the colder climate rhododendrons which I had obtained from Northern California nurseries. A few seemed to do reasonably well, but most just didn't like it here. Some simply decreased in vigor at varying rates and died. Others grew quite well and set buds nicely, but the buds never opened. Our winters were not cold enough. Others would bloom in a halfhearted way starting in the fall so that little, if any, showy bloom was left for the normal spring blooming period. I saw the same results with almost all of the many hundreds of seedlings I raised from seed obtained through the ARS Seed Exchange. A surprising number of seedlings were vigorous and healthy, but very few went on to yield worthwhile spring bloom. However, it was not all wasted effort. As the result of similar trial and error efforts over the past 20 years or so, mostly by current members of the Southern California Chapter, we now have a list of 29 recommended commercially available varieties which do well in at least some of the varied microclimates of the Los Angeles basin and nearby areas.

Bill Moynier front yard
Moynier front yard: 'Narnia', top left; 'Cristo Rey',
top right; R. loranthiflorum x R. brookeanum ,
center; azaleas, bottom.
Photo by William Moynier

But this process took considerable perseverance and dedication, and not many were willing to engage in it. In writing to Strybing Arboretum, I was hoping for a shortcut to these results. The arboretum had no recommendations for the colder climate kinds, but invited me up to talk to their head nurseryman, Pete Sullivan, and to take back cuttings of some of the new tropical rhododendrons which he had been working with during the 1960s. This I did. Not only did I subsequently find that these vireya rhododendrons were immediately very much at home in Southern California, but I was privileged to begin a lasting friendship with Pete Sullivan and, over the years, have been the beneficiary of his generosity and considerable knowledge regarding vireyas and other weightier matters.

Twenty one years have passed, and for many years now our small core of Southern California Chapter members has been successfully growing vireyas in locations widely spread throughout Southern California. In those areas where winter frosts are light, or none at all, we grow them outdoors year round in garden beds, containers and hanging baskets. Where temperatures below freezing may be sustained for more than a few hours at a time, they are normally grown only in containers or baskets so that they can be moved to protected areas when necessary. Fortunately, a large portion of the Los Angeles basin does not experience any frost during most winters. Here in West Los Angeles where Bette and I live, we have experienced below 30°F temperatures only twice during the last two decades when minimums of 28°F and 26°F occurred. In each case the only plants significantly damaged were those which had direct exposure to the sky and were more than four or five feet from the walls of the house where moderating radiant heat from the house became ineffective. About one third of the foliage was severely frost burned on the most affected plants, but the visual effects of this damage were pretty well covered over within a year by the new growth.

By the mid 1980s, interest in growing vireyas in Southern California had increased considerably. But, our present prolonged drought, which began in 1986 and is now in its fifth year, has dampened enthusiasm for many. The basic problem has not been quantity or general quality of the water available, even though some areas have had considerably less than ideal water quality over the years. The problem has been the switchover, starting in 1985, to a new water disinfectant by the largest of the Southern California water suppliers, the Metropolitan Water District (MVVD). Since that time many previously flourishing vireyas have gradually lost vigor and some have died. (With the introduction of this disinfectant, Chloramine, the MWD found it necessary to warn kidney dialysis patients to specially filter the water they use and aquarium owners to chemically treat their water to prevent health problems with their fish.) A considerable number of vireyas have been found to be quite tolerant of this chemical, information which should be of particular interest to hybridizers who may want to try to develop more hybrids tolerant of chloraminated water. Because this is very much a local problem, I will not go into further details. Suffice it to say that for those of us who live in the more favored areas, such as the western parts of the Los Angeles basin where in normal years we receive excellent quality, Chloramine free water from the eastern Sierras, this problem should disappear when (hopefully) normal winter rains return to California. For the other areas whose normal source of water is the MWD, clearly work is needed to find ways of safely neutralizing the effects of Chloramine and possibly in developing more tolerant hybrids.

Some people here have tried vireyas and have been disappointed because they either were ignorant of or did not follow some now well tested guidelines for their culture. We have found that there are really only two critical cultural requirements: use a suitable growing mix which provides excellent drainage and let the growing mix dry out almost completely between watering. I don't know if these requirements are equally critical in cooler growing areas where root rot problems may not be as great a concern, but here it is essentially a lead pipe cinch that any container grown vireya which is not treated in this way will surely die, quickly. Plants growing in the garden beds have proven to be a bit more tolerant of non-optimum dampness conditions. Fortunately, the periods of continued dampness which occur naturally during the winter, even during our wettest winters, have not been found to lead to any significant loss of plants due to root rot. Apparently the warmer temperatures of the spring through early fall period are needed for the root rot organisms to make headway. The growing mix which we have had the most experience with and which has proven to provide the good drainage required is one third coarse peat moss, one third coarse sponge rock (Perlite) and one third small, orchid mix size bark. In the raised garden beds this mix is used undiluted in the top 12to15 inches of the beds. This depth has been very adequate, even for the older, mature plants. For some of the fussier varieties, typically those with less vigorous root systems, we have found it advisable to pay particular attention to maintaining sharp drainage and we replace the mix, both in containers and garden beds, every three to five years. On the other hand, some of the older plants in the garden beds have been growing very happily in their original mix for up to 15 years now. So, periodic replacement of the growing mix is a matter of judgment and how much TLC one is willing to expend in growing these plants.

Other cultural recommendations for growing vireyas in Southern California are as follows:

1)  They should be protected from direct exposure to the hot afternoon sun. Northern and eastern exposures are preferred, but dappled shade from a tree, or equivalent, can make other exposures acceptable. Many of our plants see no direct sunshine from the beginning of November until the end of February and still grow very nicely and have normal bud set.

2)  They seem to thrive with only small to moderate amounts of fertilizer. Significant leaf burn can result from over fertilizing. Slow acting organic based fertilizers are best. I have found that a fifty fifty mix of any of several organic azalea camellia fertilizers and cottonseed meal, plus a small amount of chelated iron, applied lightly three or four times from late winter through early summer, produces healthy, vigorous plants. Soluble fertilizers such as Mir-Acid and Rapid Grow have also produced good growth on younger plants.

3)  They should be tip pinched regularly starting as early as possible and up until bud set to transform these (mostly) natural open lanky plants into well rounded shrubs of pleasing habit.

Cultural requirements for successfully germinating vireya seed are quite straightforward. Seed is readily available from Bill Moyles, who handles vireya seed distribution for the ARS Seed Exchange, and I have found the following procedure for producing healthy, vigorous seedlings uniformly successful.

For the container, use a frosted plastic container with a snap on lid of the type used for storing food in a freezer. The ones I use are four inches square and three inches deep. There is no need to poke holes in either the container or the lid. Use milled sphagnum moss as the germinating medium if you can find it. Otherwise, buy the bulk sphagnum moss used for living hanging baskets and hand grind it through a quarter or half inch wire screen mesh. This is not a particularly easy task, but it is worth the effort in terms of disease free seedlings. I have been told that sphagnum moss inhibits damping off and related fungi, and all my experience has been consistent with this assertion. Of the many hundreds of batches of seedlings which I have raised, I have never once had any fungus, or any other disease problem using this medium. (It also works equally well for others types of rhododendrons.)

Pre-moisten the moss, squeeze out the excess moisture and fill the container so that it is about two thirds full after packing down lightly. Sprinkle the seed on top of the moss and rewet the moss to about half way down. Snap on the lid and place the container in a well lighted area which receives no direct sunlight. At room temperature the seeds should germinate in two or three weeks. At temperatures which dip down into the 30s and 40s, such as ours here during the winter, it will take four to six weeks. Leave the lid on for several months until the seedlings are about one fourth inch tall (it's okay to peek as often as you wish). Then gradually introduce air over a few weeks period by gradually raising the lid.

R. 'Marshall Pierce Madison'
'Marshall Pierce Madison'
Photo by William Moynier

Only a small percentage of the better hybrids developed to date have been named and registered. As with other types of rhododendrons, there is wide variability in vireya seedlings from any given cross, so that is sometimes a matter of a pig in a poke when buying plants not uniquely identified with a clonal name. Some basic characteristics of those named varieties which I am presently growing or have grown in the past, and which I would recommend to others, are presented in Table 1. Many of these are just now becoming available or will soon be available from several mail order rhododendron nurseries. Nineteen of the 33 hybrids listed in Table 1 were hybridized by Pete Sullivan and were named and registered by him or others involved in growing on the progeny. Where a species plant which I have been growing compares especially favorably in general overall appearance and quality with the named hybrids in a given color category, I have included it in Table 1.

Table 1  Characteristics Of Some Recommended Hybrids And Species
Height At Maturity, Feet
Basic Color Low (Up To 2½) Medium (2½ to 4½) Tall (Over 4½)
White *'Aravir' (F)
*'Moonwood' (F, HB)
'Nancy Adler Miller' (F)
Creamy Yellow 'San Gabriel' (F, HB) (1) 'Sweet Wendy' (F)
Yellow * R. aurigeranum R. laetum (BG)
Orange *'Athanasius' (HB) (2) 'Ignatius' 'Mount Pire'
'Thomas Becket'
R. javanicum
Orange Yellow *'Cristo Rey' 'Belisar' (BG)
Bicolor *Vladimir Bukovsky' *'George Budgen'
'Narnia' (BG)
Salmon Pastel *'Iazarus' (F)
'Ravalac' (F)
Light Pink 'Clipsie' (F, HB) 'Dr Herman Sleumer' (F)
'Felinda' (F) 'Elizabeth Ann Seton' (F)
(3) 'John Henry' (F)
Pink 'Kurt Herbert Adler' (F) *(3) 'Cephas' (F)
Taylori' *'Marshall Pierce Madison' (F)
(4) 'Santa Lucia' (F)
Red Cream or Yellow Bicolor 'Emmanuel' (F) 'Calavar' (F)
*'Leonore Frances' (F)
Rose Red *'Cair Paravel' (F)
'Terebinthia' (F)
Red *'Ne Plus Ultra'
'Saint Valentine'
* A Moynier Favorite Footnotes: Unregistered Clone Test Name For:
(F) Fragrant (1) R. phaeopeplum x R. laetum
(HB) Suitable for hanging basket (2) R. zoelleri x 'Clorinda'
(BG) Because of open, lanky habit, best used in background (3) 'Dr Herman Sleumer' x R. leucogigas
(4) 'Kurt Herbert Adler' x R. leucogigas

Table 2 is included as a guide for helping predict what will be some of the more likely characteristics of a given hybrid when the parent species are known. The information in Table 2 reflects general characteristics which I have observed for approximately 80 relatively mature hybrids presently growing in our garden beds and containers, and perhaps twice that number of additional seedlings I have grown over the years.

Table 2  Expected Characteristics In Hybrids
Hybrid Characteristics
Basic Color
Flowers 1
Diam. 2
Fragrant Height 3 Habit
R. aurigeranum yellow M-L M No L-M rounded
R. brookeanum orange L S-M No M rounded
R. jasminiflorum white M-L S Yes L rounded
R. javanicum orange M-L S-M No M rounded
R. konorii white/blush pink M M-L Yes M rounded
R. laetum yellow M M No M-T upright open
R. leucogigas white M L Yes M rounded
R. lochiae red S S No L compact spreading
R. macgregoriae yellow/orange L S No L-M rounded
R. phaeopepium white M M Yes L-M rounded
R. zoelleri orange-yellow bicolor
M M-L No M-T upright
1. Flowers Per Truss 2. Individual Flower Diameter, inches 3. Est. Height At Maturity:
Small No.: 2 to 5 Small: 1 to 2 Same as Table 1
Medium No.: 6 to 10 Medium: 2 to 3
Large No.: 10 to 15 Large: 3 to 4½

The year round blooming habit of vireyas, at least here in Southern California, is a particularly special blessing in growing these plants. Many varieties have shown some color every month of the year, sometimes in a single plant in a single year, sometimes involving more than one plant of the same variety and more than one year to fill out all twelve months. Bloom records which I have kept for 60 relatively mature varieties over a four year period show the following - 31 percent of them to be in this category: 'Aravir', 'Moonwood', 'Narnia', 'Taylori', 'Vladimir Bukovsky', 'Athanasius', 'Leonore Frances', 'Cristo Rey', R. christianae x R. macgregoriae , R. lochiae x R. pseudonitens , R. macgregoriae x R. aurigeranum , 'Red Prince' x R. lochiae (two clones), R. gracilentum x R lochiae , R. laetum x ( R. macgregoriae x R. aurigeranum ), R. phaeopeplum x R. laetum (test name 'Sweet Wendy'), R. lochiae x ( R. konorii x 'Dr Herman Sleumer'), another R. macgregoriae hybrid and R. lochiae . Another 10 varieties have bloomed at least 10 months of the year. Although vireyas with this year round bloom habit do occasionally bunch their blooms somewhat, one to four or five blooms open at a time is the more usual pattern.

'Narnia' (R. aurigeranum x
R. zoelleri)
'Narnia' ( R. aurigeranum x R. zoelleri )
Photo by William Moynier
'Moonwood' [R. konorii x ('Pink Delight' x
R. jasminiflorum)]
'Moonwood' [ R. konorii x ('Pink Delight'
x R. jasminiflorum )]
Photo by William Moynier
'Pink Creeper' x R. laetum
'Pink Creeper' x R. laetum
Photo by William Moynier

Another group of plants among the 60 have stubbornly clung to a pattern of shorter bloom periods each year. Twelve varieties have limited their bloom to the same months each year for continuous periods of five months or less which, depending on variety, occur throughout the year. Some of these produce quite showy splashes of color sometime during these shorter bloom periods. The plants in this shorter bloom period category are: 'Calavar', 'Ravalac', 'Belisar', 'Cair Paravel', 'Kurt Herbert Adler', R. leucogigas x R. laetum , 'Kurt Herbert Adler' x R. leucogigas (test name 'Santa Lucia'), ('Triumphans' x R. javanicum ) x R. leucogigas , 'Triumphans' x R. zoelleri , 'Pink Creeper' x R. laetum , R. konorii x R. laetum , R. laetum x ( R. konorii x 'Dr. Herman Sleumer') and another R. zoelleri hybrid. The remainder of the 60 plants have bloom patterns intermediate between the two extremes. Figure 1 is a histogram for all 60 varieties. If a given variety has shown color during a given month for any of the four years, it has been included in the total for that month in the histogram.

One conclusion from all of this is that if you have even a relatively small collection of vireyas, and if (perhaps a very big "if) your climatic conditions do not produce significantly different bloom patterns from ours, you should expect to see something in bloom just about every month of the year.

Vireya Blooming By Month
Figure 1 Vireya Blooming By Month
(60 varieties over a 4 year period)

Finally, for those of you visiting Southern California in the future, you may be interested in viewing two side by side beds of vireyas growing in the UCLA Botanical Garden. The older bed was planted by chapter members in 1984 and contains about 70 now relatively mature plants. Unfortunately, at this time quite a few of these are showing typical signs of their several years' exposure to chloraminated water, especially serious leaf burn. The second bed was started in 1989 and presently contains about 20 species plants. The chapter plans to continue to add to this bed as more species plants become available. In 1988 the chapter also planted out a small bed of about 15 vireyas at the Huntington Gardens in Monrovia. This was an experiment to determine how they would do in a bit more extreme climate, especially in regard to more likely winter frosts. So far, so good. The plants have come through several winters and at last report were still growing quite happily.

William (Bill) Moynier and his wife Bette operated Vireya Specialties Nursery out of their backyard from 1980 through 1990. Bill retired from his engineering career at Hughes Aircraft Company in 1988.