EXPLORING THE UNKNOWN WITH R. CHRYSANTHUM
B.C. Potter, Port Ewen, NY
R. chrysanthum is, in all probability, a living fossil, and may very well be one of the original species that existed prior to the period of earth upheavals. It certainly is, without doubt, one of the purest elepidote species, for no other elepidote species can exist close enough to cross pollinate with it in its near Arctic habitat.
In America, R. chrysanthum is a somewhat difficult species to grow well for it requires a lot of moisture, some shade, and our summer heat is no asset to its well being. For example, I have come to believe that heat has a direct influence on the fertility of its pollen. Also, at times, it causes a few of its newly formed flower buds to expand and open out of season and the pollen taken at that time lacks normal fertility.
With such an ancient species being brought into cultivation by way of seed, and with no actual knowledge available about the species, other than its description, and its adaptability difficulties, one must learn from zip how to cultivate the plant successfully.
There is also a possibility that dead heading R. chrysanthum may induce premature flowering vigor in our drastically different climate. Actually, dead heading is an unnatural procedure. Hopefully, second or third generation plants may develop easier adaptability to our climate.
R. chrysanthum, at my place, normally flowers in late April and pollen taken during that time is 100% fertile. However, if we have an unseasonably hot, dry period during its normal flowering time, its pollen loses some of its fertility.
Out of season flowering is not a normal characteristic of R. chrysanthum. Twenty years ago, I grew from seed to flowering, more than a hundred R. chrysanthum plants. Part of my seed came from the Asian mainland and part from Japan. Both have reacted the same to the abnormal weather we have had lately.
Some R. chrysanthum hybrids, depending on the cross, will open a few flower buds in August if the temperature is very high for a week or two. However, the percentage is actually small and, as a matter of fact, I have made crosses that were in no way related to R. chrysanthum, that reacted in the same manner recently.
In mid-September 1980, a 25 year old 'Everestainum' opened a few flower buds. This never happened before.
We have a considerable number of contemporary R. chrysanthum hybrids that have never opened a flower bud out of season. Some are more than twelve years old and they have proven they can endure cold, heat, and drought, and insects rarely touch a leaf on them.
When we consider the natural habitat R. chrysanthum thrives in above the timber line, and further north than any other elepidote rhododendron can grow, one can readily understand its difficulties in the environment we are asking it to adapt to.
A plant explorer who personally visited R. chrysanthum's summit home, stated that this species is subjected to forty and more degrees below zero.
R. chrysanthum's genes for hardiness do dominate, and just about any reasonable cross, using its pollen, will produce climate hardy offspring for the area they are grown in.
This close to the Arctic rhododendron species is the only elepidote that I know of that has pure yellow genes that are capable of complete domination when crossed with pure white. All offspring are pure pale yellow.
I have been experimenting with and evaluating R. chrysanthum genes for a long time, and I find them to be powerful and of great value to me. Using the same procedure on other wild species, I now have a number of species capable of contribution to my breeding for climate hardiness.
R. chrysanthum could hardly be recommended for breeding in the very hot climates due to the impact heat has on its pollen. However, R. chrysanthum could be of considerable value to breeders located outside the normally high heat zones.
Pedigreed R. chrysanthum hybrid dwarfs are charming plants. All are well branched with good foliage that is rarely, if ever, chewed by insects, and they seem to be immune to disease. They range in size from prostrate creepers to three foot bushes. All are free flowering, most with candle broad trusses.
When I became interested in rhododendrons many years ago, there were only two rhododendron hybrids in my locality and they were in front of my home. I believe they came from Westbury Rose Co., in 1933. They were sold by color in those days, however, their beauty inspired my desire for more hybrids but I was informed my climate was too cold.
Later, I decided to do experimental breeding to see if I could develop rhododendrons that were climate hardy, ornamental, and dwarf in size. To accomplish my goal, I had to grow the species I needed from seed collected in the wild. Now we have two small experimental nurseries full, for the most part, with climate hardy, pedigreed dwarfs. All are being carefully scanned for outstanding individuals.
In closing, may I repeat a statement I have often made and that that anyone located outside the favorable zones, that can flower a rhododendron, can breed many more that will be climate hardy in that locale, and beautiful in flower.
The world's largest market is waiting for climate hardy rhododendrons - also thousands of potential A.R.S. members.