Rhododendron Breeding Methods
H. R. Yates, Frostburg, Maryland
As I look over this group of rhododendron enthusiasts I wonder who among us are the people that will follow in the footsteps of our beloved old-timers who have devoted so much of their life-time working so hard to develop better and more beautiful plants for our enjoyment. Who will take advantage of the work done by Joseph Gable, Guy Nearing, Halfdan Lem, the Hennys and many others who by their crosses between species have created so many primary hybrids for us to use as a firm foundation to build upon. I feel that if Rhododendrons are to continue to improve, most of the work will have to be done by amateur hybridists. Folks like yourselves who have such a great love of plants and with a consuming passion to create plants with better habits, purer colors, and most of all the needed hardiness to enable them to grow and to flower in the harsher sections of our country. Folks who will accept the challenge as a "Labor of Love", as there will be few who will become wealthy from their efforts at hybridizing.
I believe the improved plants of the future will not come from the large commercial growers who depend on their business for a living, but instead from the small scale gardeners who grow them as a hobby. I consider myself in this category and though perhaps my experiences may be of some value to others who would like to enjoy the thrill of seeing, for the first time, the opening blooms on the things they helped create. I know Mrs. Yates and I live from year to year waiting for Spring to arrive and each day we can hardly wait for morning to come to see if a new bud has opened. I sometimes catch heck for helping them just a little bit. In fact, I must confess we have been seen roaming around in the garden with flashlights at two a.m. or maybe three a.m. I have become a little wary of these nocturnal excursions since I just about stepped in the middle of a fat old mother skunk who was escorting her family on a moonlight tour of the garden. I have loved flowers since my childhood and get so much satisfaction growing and experimenting with them. I guess this is the reason for me becoming "A Do It Yourself Hybridizer and Grower of Seedlings." I began experimenting with seedlings under fluorescent lamps about eighteen years ago. I got off to a slow start, not having too much success until I read a paper by Guy Nearing in the October, 1957 A.R.S. Bulletin. He wrote of his experiments with various mosses, stating he felt that there was an antibiotic effect on seedlings that helped prevent damp off, and that seeds in the wild seemed to thrive when they fell into the damp moss and germinated. This article sparked the idea for some experiments, and I am indebted to Mr. Nearing for his information.
When I started raising seedlings, I gathered any seed I could lay my hands on. It is a pity I wasted so much time on seed that had little chance of producing anything good. Where was I to get seed of something worthwhile? One spring Mrs. Yates and I, after admiring our one plant of 'America' and one 'Roseum Elegans' decided we just had to see more rhododendrons. We had read in The Saturday Evening Post of a man in Pennsylvania who had a whole farm of them. So we set out, and after a long drive through Maryland and through winding roads of Pennsylvania Dutch country, we finally found Joseph Gable and his many plants. The sight that met our eyes almost took our breath away. If we had been bitten by the rhododendron bug before, when we met Mr. Gable and his plants, that old bug just about snapped a chunk out of us.
After several trips back to Stewartstown, I begged Mr. Gable for some seed - not good ones, just anything he would find for me to experiment with. He grinned and said "Well now, if you are going to try and grow plants, you might as well have seed of something that could turn out to be good. I will send you some this fall." I believe I was as thrilled about this as I was with my first kiss, remembering what a problem it was for me to get any good seed until I met Mr. Gable. I feel the work Mrs. Esther Berry has done, by heading up the seed exchange, has removed any real obstacle to anyone willing to get into the act. I suggest bouquets for Mrs. Berry and her willing helpers and to the contributors of much fine seed that has opened a gold mine of opportunities for the beginners who now don't even have to have a rhododendron plant of their own.
Since our members are scattered over much of North America and throughout the free world their requirements are so diverse it would be difficult to formulate a recipe for crosses that would meet all their needs. The dedicated hobbyist however, will soon determine by studying the fine books "Rhododendrons of the World" by Dave Leach and "Rhododendrons and Azaleas" by Clement Bowers, what species have the qualities he would be looking for. He could then select crosses from the seed exchange that most nearly meet his requirements.
As mentioned before, I live on Big Savage Mountain, the coldest spot in Maryland - indeed a dismal spot to grow anything, my goal must be for extreme hardiness. For example, the ironclads are not all reliably hardy with me. I have found the toughest of them are 'America', 'Mrs. C. S. Sargent', 'President Lincoln', 'Roseum Elegans' and 'Nova Zembla'. So you can see I just can't forget hardiness ever.
I have made many crosses using plants and pollen of the hardiest things Mr. Gable has produced, always trying to take advantage of the work he has done by using his primary hybrids for crossing and by growing F2 generations. I have high hopes for 'Catalgla', the Gable selection of white R. catawbiense , I have tried many crosses with its blood in the parents, using such primary hybrids as 'Catalgla' x R. fortunei , 'Catalgla' x R. discolor , 'Catalgla' x R. yakushimanum and other. I expect much from the crosses 'Catalgla' and R. fortunei . I will show you a slide of one of my plants of this cross that has flowered after 27 degrees below zero.
I also have high hopes that some day a hardy deep yellow will result from a cross of the pale yellow 'Catalgla' x R. wardii to be named 'Joe Gable'. I have many seedlings of this one crossed with the finest yellows available.
Mr. Gable has given me much sound advice that would take far too much time to cover but a few things he has often repeated are; 1 - If you want to raise hardy children, you must select hardy grand-parents. 2 - Have the nerve to discard a plant as soon as any faults are noticed in the growth habit. I have tried to follow these rules and always try to have some hardiness in my crosses. Although I have tried some pretty wild crosses, especially in trying for yellow, since my space is limited, I must be ruthless and discard any seedlings showing any signs of tenderness. Out they must go.
Before I show you slides of some newer rhododendrons, I would like to take a few minutes for a brief description of my seed boxes and growing habits. I will not go into great detail as it is covered fully in the July 1966 A.R.S. Bulletin, however I would not recommend, as mentioned in the Bulletin, the fertilizer three times a week - make that every three weeks.
The seeds are sown December 1, in plastic perma nest trays in boxes that could be called modified Glendale propagators. These boxes are in my basement, where the average winter temperature is around 60°F. I use three four-foot tubes, a foot above the seedlings. The lamps are Grolux until the seeds germinate, then they are changed to one Grolux, one warm white and one cool white. These lamps are on fifteen hours daily. When the lamps go on in the morning the temperature in the boxes is around 65°. As the lamps provide some heat, the temperature will rise to 74° to 75° when they switch off in the evening.
My planting medium consists of the following mixture: one part woods soil, one part clay loam, one part coarse sand, one part sphagnum peat. This is screened through a quarter inch screen and sterilized. The trays are prepared by first using a half inch layer of sand for drainage. Then the planting mixture is pressed down with a brick, leaving about three quarter inch of room at the top. On top of this I spread about three eighths inch of a mixture of fresh ground wood moss, with a little fresh sphagnum. This is ground through a meat grinder and mixed with about one fourth gravelly woods soil. This top layer of soil is not sterilized as we want it to grow. After pressing down the growing medium and thoroughly watering the trays, the seed is shaken on top of the mixture and not covered except by panes of glass which are left on, except for inspection, to make sure the surface does not dry out until germination is well underway. This usually takes from eleven days to three weeks.
If the seed has been properly ripened, I like to leave my seed capsules on as long as safely possible, at least until they have been touched by frost. I would not argue about this, but I feel that the longer the seeds are in their capsules on the mother plant the better they develop, and the more virile they become; resulting in better and more even germination - thus producing more vigorous seedlings. After most of the seed has germinated and the glass has been removed, I wait about three weeks then begin giving them a feeding of Liquid Blue Whale - about a teaspoon to a gallon of water. This feeding is continued every two or three weeks. I use a small Dron Wal Pressure Sprayer for watering - using warm water but not getting the nozzle too close to the seedlings. Don't use the Liquid Blue Whale in the Pressure Sprayer, it will foul it up - use a bulb sprayer for this. (About a pint and a half of water is plenty for 24 8" X 12" trays don't over water.) A good indicator of correct watering is when the moss continues to grow nice and green with no brown spots.