Rhododendrons From Seed
Jack Cowles, Wellesley, Mass.
Reprinted from "The Rosebay" Massachusetts Chapter Newsletter
One of the most intriguing and yet deceptively simple things to get bitten by is the rhododendron seedling bug. While probably eight out of ten of us are perfectly happy to have and succeed in growing some plants of 'America,' 'Roseum Elegans' or 'P.J.M.', there are always a few who are different.
There are many reasons for growing seedlings, once you qualify on the basics. To get the basics you just try each step in turn. Get the seed, sow it, grow and plant the seedlings. Eventually you find out what the results are. Behind the excitement of planning and producing lies the dream of bedazzling the world with something new. The challenge comes when you realize what the tremendous possibilities are, and how much needs to be done. We in New England can only turn green with envy at what is being grown on the West Coast, in England and in the rest of the 'Rhododendron Climates.'
One nice thing about being a seedling grower today is that much of the pioneering work has already been accomplished. Charles Dexter and Tony Consolini in our area, and within the same era Gable and Nearing, are recognized for their accomplishments. They produced hybrids that are important in the nursery business today, as well as providing material for further hybridizing. Fortunately all those really dedicated to rhododendron improvement have been remarkably generous with their materials and knowledge.
The real "moon landing" in rhododendron research, in my opinion, happened with the formation of a 'seed exchange' by and for members of the American Rhododendron Society. Most of us don't fully appreciate how important this step is, but it can and already is beginning to open up tremendous possibilities. It speeds up what used to take a lifetime to accomplish to a matter of relatively few years. If enough people participate in the effort, lack of imagination will be the only limit in bringing about improved forms.
If you intend to try some seedling rhododendrons, you must either have a seed supplier or else produce your own. Each approach has its advantages. Usually there is quite a wait involved when you depend upon another source. If you harvest your own, you can process the seed and sow it in only a few days.
With the arrival of October's cool nights the seed pods seem to accelerate their ripening. The first sign of maturity will be the pedicel turning yellowish and wrinkled. (The pedicel is the short stem at the base of each capsule, which connects it to the main truss). The pod will not develop any more and can be picked at this stage. If left too long, the valves of the fruit capsule open, spilling out the seed to the wind. Usually it will be found that large-flowered types produce large (2") fruits, as in the case of R. fortunei. R. racemosum, which has small flowers, has correspondingly small (¼") fruits. Evidently there is a correlation between flower and pod size.
While one is picking the pods, a system is needed for recording the identity of the different kinds. It is simple to use an envelope for each, writing on the envelope what it is. Sometimes it is well to include the field label with the pods, if it is legible.
The pods, kept in half-open envelopes, will dry out and become crisp after 3 to 5 days in house atmosphere. They can be lightly crushed with a block of wood or a pair of pliers. The seed can then be teased out of the valve segments or strained through a tea strainer. It is well to work over a piece of stiff white paper, and pour the seeds from this into labeled envelopes. One word of caution: some people are allergic to the resin in the dust, so if you have never handled seed before be on guard against a sneeze.
The seed itself varies from very fine and dark as in R. carolinianum and R. racemosum to the relatively large, winged and buff-colored R. fortunei.
Once it is processed, dry seed can be either stored or planted immediately. Longevity in storage depends on two factors - cold and dry. Ordinary room storage is all right for six months. If you plan to store the seed for a longer period, make sure it is thoroughly dry, put it into glass jars with tight lids, then place it in the freezer. I have had excellent germination from some seed after five years of freezer storage.
Generally one seed pod can supply several hundred seeds. It is well to consider the space and time that will be needed in caring for the subsequent progeny. But the most important consideration should be given to getting seed which stands a chance of producing what is expected of it. In the case of a species, it should be the finest form that approaches what you might be seeking. There is always a certain amount of variation in seedlings, so don't expect absolute uniformity.
When growing seedlings of hybrids, one should expect great variation, because that is what hybridizing is all about. In general, the closer one stays to one's own yard for seed source, the better is the probability of survival. The exotic sorts often do not stand the rigors of our climate.
For the first two seasons the seedling is very vulnerable to extremes in temperature, light and water. After two years the average seedling can be grown the same way rooted cuttings are. Seedlings make up for this two-year handicap by the promise of variety and uniqueness. It is the lure of something new and perhaps superior which challenges the seedling grower.
Also in favor of seed is the fact that the initial cost is relatively low. The question is: What is available for crossing, or else where can one obtain seed? A few seedsmen offer some. The American Rhododendron Society publishes its seed exchange list yearly. In it are seeds of rare and elite forms of species, plus hybrid seed promising some of the most advanced "models" off the line.
One word of advice, before you start. This habit is a hard one to break, and once you succeed, you're hooked for life!