QBARS - v21n4 Adventures in Rhododendron Hybridizing

Adventures in Rhododendron Hybridizing
Ben Lancaster, Camas, Wash.

At the suggestion of several rhododendron acquaintances with whom I have either met or corresponded for many years, I offer these notes on our hybridizing experiences at Lackamas Gardens, Camas, Washington.

My permanent addiction to rhododendron culture came about when a friend loaned me a copy of Dr. Clement Bower's excellent book on rhododendrons. A convalescent at the time, I studied this book from cover to cover and became impressed with the great number of distinctive species described therein, as well as their very wide geographical distribution in Mother Nature's garden plan. Sensing the wonderful possibilities of creating new and more suitable plants for home and garden decoration through hybridization, I immediately started making a collection of well over a hundred species as a foundation for a breeding program. Whenever certain species we desired were unobtainable. we were forced to settle for primary or even more complicated hybrids containing the bloodlines we wished to incorporate in our breeding. Our experience indicates that many of these hybrids of known parentage, when used as parents, are quite often superior to the original species. In fact, our final conclusion in the choice of parentage was that we, as well as other modern breeders, have missed one of our best bets by not taking advantage of the many years spent in selective breeding by others, of both the older and more modern hybrids. Many of the older hybrids have excellent plant form and flowers. A great number are bone hardy and more adaptable to adverse growing conditions than some of the modern hybrids.

By all means, cross the best forms of your species with some of these hybrids by others. If you are interested in producing hardy hybrids with stamina enough to succeed wherever rhododendrons culture is at all feasible, try crossing some of the best of the ironclad hybrids with hardy species of more recent introduction that have not as yet been used to any great extent. The careful study of the Royal Horticultural Society's Rhododendron Stud Records provides fine illustrations of the plant types that have to date produced varieties of exceptional merit. We plan all of our crosses with definite objectives in mind. The shotgun method of pollination, used by orchardists to produce fruit, seldom produces worthwhile varieties in rhododendrons.

Heat Tolerance

In our selection of parents, for many years we have considered heat and sun tolerance along with hardiness. By using our very hardy, low growing form of R. williamsianum as seed or pollen parent, we obtained one of the lucky breaks we were searching for in the creation of a compact, dwarf to semi-dwarf, group of hybrids we call our "Bells Series." In this williamsianum hybrid group the use of various species and hybrids has given us many different color variations with degrees of hardiness, heat, sun and wind tolerance, well beyond our expectations. We attribute most of this stamina to the form of williamsianum used, as this plant has withstood temperatures down to -20°, even when planted in containers above soil level. The only one of this group that grows a bit stronger is 'China' X R. williamsianum ('Glad Tidings'), whereas the reverse cross 'Easter Bells' shows more of the williamsianum characteristics.

R. yakushimanum as a Parent

In crossing some of the older and newer hybrids with some of the more recently introduced species, we have used the F.C.C. form of R. yakushimanum since 1959 with splendid results. We doubt very much that anyone will ever produce anything in a white Rhododendron better than some of the finer forms of R. yakushimanum itself. However, plant breeders are forever trying for new colors in better plant and foliage forms. So far, R. yakushimanum seems to be one of the answers for us.

After making more than 75 R. yakushimanum crosses with various hybrids and species we found that it produces viable seeds quite readily with almost any of the non-scaly types. Its many excellent traits seem to be dominant in all of its hybrids. For many years our formula for the final selection of plants for introduction has been points such as the following, in about this order. Plant form including foliage; leaf persistence over a number of years ( we prefer a well-clothed appearance rather than a mini-skirt or bikini effect); flower and truss form, including good substance; eye pleasing colors, of course; cold and heat tolerance; firm or heavy caliper growth shoots (we have discarded many with branchlets too weak to support their flowers properly); length of time for cutting grown plants to produce bloom (we waited twenty odd years for a seedling form of R. galactinum to produce bloom before we discovered that its easily rooted cuttings usually produce blooms at from one to three years.)

Plant Characters

Our final test, before a clonal selection is made, is its ability to strike roots readily and how it performs as a rooted cutting. In most instances we have found the cutting grown plants are superior in every way to the original seedlings. In fact, from several seedlings of known potential, but with one or two faulty growth habits, we have grown cuttings that have produced ideal plant forms. To name just one instance, R. chlorops X R. williamsianum produced excellent plants and flower forms with the exception of one straggly plant, that happened to have the most yellow flowers of all (straw yellow), named 'Ivory Bells'; cutting grown plants have perfect form.

In our experience yakushimanum hybrids as a group measure up more consistently to our plant ideals than any species we have worked with, with williamsianum for dwarfish forms, a close runner up in importance. 'Lackamas Spice' ( R. chlorops X R. diaprepes ) X R. yakushimanum ) gave us the same spicy fragrance as the pollen parent. R. yakushimanum crossed with 'Mars' gives blends of rose madder or phlox pink; with the old ironclad 'Chas. Dickens', an unfading pastel fuschine pink, with up to 24 ruffled flowers per truss, with several clones of deeper colors. With R. smirnowii we get ruffled flowers in 6" trusses opening pink; turning pure white, on plants difficult to distinguish from yakushimanum itself. Its maiden blooms seemed a lot more attractive than either of its parents. With 'Vulcan's Flame', came clear pastel phlox pink and deeper blends of rose madder, with several clones very reminiscent of yakushimanum form and leaf.

The above is a small sample of one year's breeding, plants which set from three to six bloom buds in their third year from seed. Several different clones of at least sixteen other crosses from the same year's breeding are well budded.

Among the 1959 crosses are several very fine clones including seven of our R. chlorops P.A. X R. yakushimanum , all of which have produced mimosa yellow or primrose yellow flowers in pastel shades on plants of excellent form with no indumentum.

Indumentum

Regarding the question of indumentum on primary hybrids of R. yakushimanum , our experience indicates that in crosses with the species, or primary hybrids of R. griersonianum , or their like, indumentum will appear in varying degrees on all of the seedlings. Crossed with some of the older, deeper colored hybrids, created at the time R. arboreum was the hybridizer's principle source of red or pink colors, almost all of the seedlings will have forms of indumentum intermediate between the plastered arboreum forms and the thinner wooley types. Occasionally such indumentum will be quite highly colored. In crossing R. yakushimanum with R. fortunei or similar species, or their hybrids, that have no indumentum in their background, we haven't obtained any trace of indumentum.

The one thing of which you can be reasonably sure is this: whatever the size or ungainly proportions of the plant with which you cross R. yakushimanum , the progeny will be reduced to garden size in sturdy, many branched dwarfish to moderate growers. Being of comparatively recent introduction, their ultimate size is anyone's guess.

R. chlorops as a Parent

Another one of our favorite parents at Lackamas Gardens is our R. chlorops 'Lackamas Cream' P.A. The variety name was suggested by Dr. Fletcher after he and Mr. Davidian had identified it from requested herbarium samples mailed to the Royal Horticultural Society at Edinburgh, Scotland.

In a conversation with Dr. Fletcher at the International Rhododendron conference in Portland, Oregon in 1961, he informed us that R. chlorops was grown from a packet that should have contained Acer seeds according to the herbarium specimen number, in one of the later collections by George Forrest.

Placed in the Series Fortunei, it has withstood minus 20 degrees over a 10day period here without injury. Its yellow genes seem to be dominant in its F1 and F. hybrids. Our hybrids from it, which have received A.R.S. P. A.'s included 'Inca Gold', 'Lackamas Gold' and the fragrant 'Lackamas Spice'. Its blue green foliage and other splendid traits are very apparent in succeeding generations, even to its pest-resistant qualities, especially to root weevils.

Breeding for Yellows

In the production of more vivid yellows we had long toyed with the idea of introducing orange and scarlet genes into our yellow breeding. To report on one or two of such crosses that have bloomed to date, 'Medusa' X 'Lackamas Gold', gave us burnt orange buds opening delft rose which turned to a rich amber yellow when fully opened. Plants were of excellent form. Of the selected clones growing from this cross, the three that have bloomed are very similar. 'Indiana' X 'Inca Gold' produced 4" primrose yellow flowers with up to eighteen per truss on rather vigorous plants. It must have been the scarlet and orange genes from the two parents of 'Indiana' that combined with the yellow genes of the R. chlorops parentage of 'Inca Gold' to produce this clear yellow which we named 'Aztec Gold.'

We have had similar reports on the use of 'Medusa' and 'Indiana' from other breeders. Incidentally our form of 'Indiana' ( R. scyphocalyx X R. kyawii ), the latter a very tender species, is surprisingly hardy, having withstood below zero temperatures here many times. In our thinking R. scyphocalyx which is listed as a subspecies of R. dichroanthum , together with its hybrids, may very well prove more valuable in the creation of yellow hybrids than R. dichroanthum itself.

R. chlorops X R. campylocarpum var. elatum , gave us larger primrose yellow flowers than its pollen parent, with the added stamina of R. chlorops . We have one plant of Hookers' form of R. campylocarpum , which is a much neater and more dwarf form, with a bit brighter yellow flowers than the taller elatum form, which has many award plants credited to its parentage. We believe the Hooker's form should be more exploited as a yellow parent and are so doing ourselves in recent years.

R. chlorops X 'China' produced large clear primrose yellow flowers much more yellow than either parent with prominent red nectaries on well formed, sturdy plants.

R. lacteum Crosses

R. lacteum , long considered the finest of the yellow species (as well as the crankiest grower) has intrigued us for many years. Finally we broke down and made a few crosses, using pollens imported from England, and from the Del James grafted plant growing here in the Northwest. Both of these forms are considered among the finest representatives of this lovely species.

In 1966 we bloomed two plants, that had set several buds in their third year from seed of R. chlorops X ('Golden West' X 'Mariloo'). 'Mariloo' is 'Dr. Stocker' X R. lacteum , 'Golden West' being R. fortunei X R. campylocarpum . With only ¼ lacteum blood in its makeup the lacteum influence was plainly discernible in plants of excellent form, grown in full exposure. Colors of the two clones were clear sulphur and mimosa yellow respectively, on plants with four to five buds set on three-year seedlings. First bloom on R. chlorops X R. lacteum this spring (1967) was barium yellow with lacteum-like foliage.

Of the dozen plants of this cross held for trial, it is difficult to distinguish the foliage on some from the distinctive deep green leaves of R. lacteum . Others tend to follow the chlorops leaf form, texture and color. They seem to have retained all of their leaves to the present in their fifth year from seed. All are sturdy, well formed plants grown in full exposure which they seem to enjoy. Our next step will naturally be to cross these two above mentioned R. lacteum hybrids and perhaps inject a few orange genes to deepen the already present yellow pigments.

Several younger R. lacteum crosses we have growing, seem to follow the same general pattern which must have been good luck, as many reports we have react about Lacteum breeding have been somewhat discouraging. Among the plants we have crossed with R. lacteum successfully, are: 'Cunningham's Sulphur', 'Lackamas Gold', 'Lackamas Spice', R. wardii X 'Loderi', 'Goldsworth Orange' and R. chlorops X ( R. wardii plus R. fortunei ), two pollens combined on the same stigma quite by accident. When I realized what I had done, I remembered that an old friend of ours, a Mr. Parker who had worked as a youngster with Luther Burbank in his plant breeding program, told me that Mr. Burbank had explained the possibilities of making such a double pollination to his young helper during a rest period. This was all beyond my meager comprehension. However after growing about a dozen of this cross to blooming size, we found all different in every respect from the single pollination using the same pollens I had combined in advertently.

Getting back to R. lacteum parentage, I am reasonably sure that by interbreeding the above R. lacteum hybrids, we have the foundation for an excellent strain of yellow hybrids. The most of these lacteum crosses have been widely distributed as 18 month old seedlings in the hope that others might take part in this lacteum hybrid adventure. With the scant experience we have had, our best guess is that the only real success with this exotic species will come from growing it in hybrid forms. At this time we have a two-year seedling of 'Lackamas Spice' X R. lacteum in full bloom (4/26/67). A pale primrose yellow, 7 in. globe truss of sixteen 3 in. flowers was borne on a 4 in. plant. This plant was lifted from a field bed, as the bud started to swell, and bloomed in the cool house.

Large Leaf Species

Our only experience with the big-leaved species is with R. macabeanum and an excellent pure white form of the only bone hardy member of the Falconeri Series, R. galactinum . When it finally bloomed, we made a cross we had planned at least twenty years before, using pollen from a fine yellow form of R. macabeanum growing here in the Northwest, and grew some sixty odd plants of which we retained only six, the rest being distributed to our friends under parentage record. With a small supply of pollen left we used it on several other yellow hybrids of ordinary form. Among these now growing in the test plots are: 'Idealist' X R. macabeanum and 'China' X R. macabeanum .

With several other macabeanum crosses growing among our local hybridizing friends, we have an excellent chance to produce a new strain of large leafed hybrids. In fact several of our friends have made some of their first crosses at Lackamas Gardens. The constant swapping back and forth of pollen, seeds and small seedlings, has promoted a comradeship unequaled in any avocation.

Using R. griersonianum

R. griersonianum , in our experience, has only one worthwhile asset as a parent, aside from its ability to root easily, namely, its ability to transmit its geranium scarlet genes to succeeding hybrid generations. We have made many R. griersonianum crosses and discarded many seedlings because of poor plant form. Typical entries from our breeding record book disclose facts like the following: R. griersonianum X 'Azor', results negative. Too much griersonianum blood gave poor plant form; R. griersonianum X 'Fabia', the same.

Evidently there is nothing to be gained in back-crossing a griersonianum hybrid with R. griersonianum . 'Essex Scarlet' X R. griersonianum , results negative. Griersonianum-like flowers on poor plant forms-Discard! It so happened that I had moved the one perfect plant form of this cross from the test row before blooming age without my wife's knowledge. When it came into bloom, she as the official record-keeper, typed the following notes just below the last above discard notation. Her following description which we used in its registration as 'Lackamas Firebrand', reads in part as follows: "Were we ever mistaken! There were eighteen 2½ in. flowers in the truss, H.C.C. currant red, leaves persistent to four years, round sturdy bush with ideal growth habit, three feet tall at ten years." The foregoing entry may serve to illustrate the importance of keeping accurate stud and descriptive records to those beginning any kind of a plant breeding program.

I have been very fortunate in having a typist wife who has made such entries in triplicate, loose leaf, indexed book form. This enables me to do this paper as a part of my winter armchair gardening.

We always try to make reciprocal crosses whenever possible, as we had noted many different plant characteristics such as amounts of seed produced, their viability, plant form, general health of seedlings, etc. depended upon which plant had been used as the seed parent.

Reciprocal Crosses

Our experience seems to indicate that seedlings from reciprocal crosses GENERALLY develop plant forms and growth habits resembling the seed parent. The greater the difference in plant size and type of the parents used, the more evident these parental traits will be noted. Our 'Bluette' ( R. impeditum X R. augustinii ) is a classic example of this, our reciprocal cross of 'China' X R. williamsianum , 'Glad Tidings', and reverse cross, 'Easter Bells', another.

Regarding reciprocal crosses, our breeding with R. thomsonii was very interesting. R. williamsianum X R. thomsonii gave us plants more consistently on the dwarf side, with a much greater seed production, than the reverse cross. Flowers on all were cherry red which prompted the name 'Cherry Bright' for the selected clone. The reverse cross, R. thomsonii X R. williamsianum , produced only a small amount of seed, which developed into a little larger growing plants with slightly larger leaves. The deeper colored red plant of this cross was named 'Currant Bells', from its H.C.C. reading. However, the cutting grown plants of these two crosses have the same bushy, globelike habit, the lighter and deeper colors being the only difference.

Some strange things happened in reciprocal crosses between R. thomsonii and 'Earl of Athlone' which might in part he the result of the oft-used term "hybrid vigor." R. thomsonii resents pruning, is subject to die-back, is finicky about its planting site and almost impossible to propagate from cuttings. 'Earl of Athlone' is rather difficult to root, produces blind eyes in its leaf axils toward its branch tips, especially while young, which rules out tip growth pinching to produce a compact growth habit.

The above described faults of both parents disappeared completely in all of the seedlings of these reciprocal crosses. Flowers of both had the same heavy, wax-like substance of R. thomsonii in cardinal red colors. The rather glossy, heavy textured leaves were unspotted in full sun at 107 degree temperatures which scorched many of the standard hybrids growing in the same open exposure. Both had fuller, rounded trusses than either parent.

The only apparent difference between these reciprocal crosses was: with R. thomsonii as seed parent, all of the seedlings produced flowers with the usual flower parts, while all of the seedlings with 'Earl of Athlone' as seed parent, produced flowers completely devoid of stamens.

I am sure everyone has noticed the long lasting qualities of these stamen-less so-called "mule" flowers. Apparently with the lack of its own pollen to spur seed production, the corolla persists indefinitely to attract insect attention. To use the term "mule" to describe stamen-less flowers is misleading as we have noted that they set seed as readily as any Rhododendron when pollenized from other plants. We often refer to such plants as "Maiden Ladies," perhaps because their floral beauty lasts so long. Both of the foregoing hybrids were named and registered after the selected clone of R. thomsonii X 'Earl of Athlone' won top honors by A.R.S. judges in the New American Hybrid Class.

'C. B. van Nes' X R. thomsonii gave us an iridescent currant red with foliage more like its seed parent which is in the 'Queen Wilhelmina' X 'Stanley Davies' parentage group from Holland along with 'Britannia', 'Earl of Athlone', 'Unknown Warrior', and several other varieties of like value as parents. These above mentioned hybrids are surprisingly hardy for R. thomsonii offspring, having tolerated below zero temperatures here several times.

Whenever we wish to introduce R. thomsonii blood into a cross we are using our hybrids to better advantage than the species itself. We find that these crossed with R. williamsianum produce sturdier wood on the same dwarfish type plants.

For Late Blooming

After making many crosses on a very fine form of R. auriculatum that is often in full bloom in mid-August, without producing seed, we decided to use it in hybrid forms that bloomed earlier. Having three plants grown from seed sent from England during the second World War, of the 'Nereid' X R. discolor cross which were rather late bloomers themselves, we crossed one of these named selections, 'Peach Lady' with "Aladdin' A.M. ( R. griersonianum X R. auriculatum ). A rather strange mixture of excellent blood lines occurred. The quarter auriculatum influence was very evident in the sturdy growth habits, leaf structure and flower forms in all of these seedlings. The up to five in. flowers were of heavy substance with up to 18 per truss and lasted very well in the late June and early July sun where they were grown in full exposure. Flower colors ranged from pure white through phlox pinks to delft rose in solid colors with unusual blends of the same and other colors including Chinese yellow. Among the five selected clones was a salmon pink with typical R. auriculatum fragrance. Only one of the deeper colored clones has been registered as 'Aladdin's Light'. A glowing delft rose with lily-like stigma and anthers. We were pleasantly surprised when these seedlings started blooming in their sixth year.

The only R. forrestii var. repens hybrids we have bloomed to date are 'Earl of Athlone' X R. forrestii var. repens . This is a rather dwarfish, sturdy, upright globe form with excellent persistent foliage, and 2½ in. wax-like blood red bells. Easily rooted, we will find a name for it as it seems superior in every way to either parent. As a low, creeping plant, our form of R. forrestii var. repens is very satisfying, but more difficult as a parent than the above repens hybrid which we have used in several crosses.

Origin of Snow Lady

We had tried to grow R. leucaspis for years without success until a collector friend, Mr. Tucker, gave us a few cuttings from a plant that had been sent to him by Lionel de Rothschild as R. leucaspis many years before. One of these cutting grown plants, which grow well from Yokohama, Japan, to San Diego, California, and in the Eastern Seaboard States, was placed in the Portland Test Gardens. When informed that this plant had been given an award with the request that we give it a name and provide its parentage and botanical description, for A.R.S. registration, we used 'Snow Lady' as a descriptive name giving the parentage as R. leucaspis X R. ciliatum . We had previously decided that this must be the parentage from a careful comparison of the botanical descriptions of these two species. This was further confirmed when we later observed the same recorded cross made by a friend in Eugene, Oregon which was an exact duplicate of 'Snow Lady.'

As 'Snow Lady' was much hardier than its parentage would seem to indicate, we crossed it with our hardy, pure white form of R. moupinense. This cross gave us a sturdy dwarfer form than 'Snow Lady' without the spindly, spreading habit of R. moupinense . Easily rooted we will register this as 'Snow Sprite'.

R. racemosum X 'Snow Lady' gave us an exact duplicate of the seed parent in a sterile, or apomict, form that doesn't seem to set seed. The well known propensity of R. racemosum to well nigh seed itself to death and the awkward deadheading procedure on these dwarf lepidote types makes this a very useful plant for the garden.

Through the years we have noticed several crosses like the above where no hybridity was evident in the seedlings and have grown several to blooming age with like results. These are without doubt apomicts, or possibly, haploid forms, useless for further breeding, and may occur occasionally in either lepidote or elepidote rhododendrons.

Crossing Lepidotes with Elepidotes

In regard to crossing lepidote types with elepidote rhododendrons, our Camas friend, Dr. Arthur Harris, working on the theory that a similar chromosome count was the most important factor in this line of breeding, has made many such crosses that definitely show both parents in their offspring. Some of these have already produced a second generation.

We have explored this line of breeding very little, but our successful cross of R. macrophyllum X R. tephropeplum is a very interesting plant. Its leaves are about half the size of R. macrophyllum with the glossy texture of R. tephropeplum on a compact dwarfish plant that grows well in full sun or shade. The flowers are orchid pink in a neat 3½ in. to 4 in. truss. It roots readily.

We believe that this line of breeding presents distinct possibilities for a new race of hybrids. One of the most attractive dwarf plants we are now growing is the cross R. williamsianum X 'Fragrantissimum' given to us as a tiny seedling by Dr. Harris. Both parents are very evident and we hope for a bit of fragrance when it blooms.

Fragrance in Rhododendrons

We have felt for many years that rhododendron breeders had neglected fragrance in their selection of parents. Most have seemed content to leave fragrance in the Azalea or Maddenii series with R. occidentale as a prime factor for deciduous types and R. mucronatum in the evergreen class to name only two of such.

In our original R. occidentale X hardy Ghent hybrids, where all the progeny were very fragrant, we intensified this by re-crossing with the very yellow form of R. luteum often referred to as A. pontica . One of the most brilliant yellows of this cross has the combined fragrance of both parents. Fall foliage was more brilliant in color as an added bonus.

In our experience members of the Fortunei Series have given us the most fragrance. R. decorum X 'Azor' gave us 'Old Spice' a blend of phlox pink and apricot with spicy fragrance. R. chlorops X R. diaprepes gave us several fragrant clones, one of which received a P.A. as 'Lackamas Spice'. Another had the fragrance of freshly cut comb honey. The number 4 clone which is my wife's favorite of this group, holds its delicious fragrance as a cut truss for at least a week's time, or until the flowers have dried and shriveled completely.

We believe that a fragrant section should be added to the classifications in rhododendron shows, for both species and hybrids, in both elepidote and lepidote sections. Such a class would surely be an incentive for modern breeders to work toward more fragrance in their choice of parents.

Our experience at Lackamas Gardens with fragrance has already developed a cult of "Rhodo Sniffers" among our friends who check the maiden blooms of our efforts every spring. To those who have enjoyed the dainty fragrance from a group of Loderis in full flower, I feel safe in the observation that much more fragrance already exists in hardier plant forms than in the exotic semi-hardy Loderis.

I am confident that the challenge for more highly colored, fragrant varieties will be met when breeders channel their skills in that direction.

We have a very promising group of 'Mars' X 'Loderi' as yet un-bloomed in which we hope to obtain some of the Loderi fragrance, for further breeding along these lines. Incidentally we have found 'Mars' a splendid parent. It seems to promote "heat tolerance" as well as hardiness in its offspring. Our 'Vulcan's Flame' (reverse cross of the English 'Vulcan') seems to thrive in the Midwest and along the eastern sea board states. It is also one of the few hybrids that will tolerate the extreme summer heat in Mr. K. Wada's Yokohama garden.

'Mars' X (red) 'Day Dream' gave us splendid plant and flower form in a currant red, which we consider better than either parent, judging from its maiden bloom in 1967.

In conclusion, a paper like this could go on and on and scarcely scratch the surface of what is already known about rhododendron breeding, not to mention the new discoveries that are being made yearly by those seeking to improve this genus through hybridization. Many of us have traveled up blind alleys that have been traversed by others to disappointment.

The big "Joker" in this deck is that only the successes become known and the failures or "what not to do" aspects of this line of endeavor, which are equally important, never come to light.

Theory is the father of all innovations. We all have theories, but until proven they will never be a substitute for experience. This trend of thought, and the prompting by others, is chiefly responsible for these notes on a few of our successes and failures in rhododendron hybridizing at Lackamas Gardens.