Thoughts on the Propagation and Growing of Rhododendrons
by Roland de Wilde, R. D. L., Bridgeton, N.J.
To accurately evaluate the various methods of propagation by asexual means, it follows that there must first be an understanding of the various methods. In the last few years, so much has been done in improving the techniques of rooting cuttings, that it has become fashionable to condemn grafting, and this condemnation very often comes from people who cannot graft anything successfully and know nothing of the principles behind it.
It is not my purpose here to go into a long discussion of the various reasons for grafting. In Rhododendron propagation it has been used for at least a half century, and until very recent years, the great majority of named varieties of rhododendron hybrids were grafted.
In the case of most ornamental plants, the idea of grafting is to supply a more or less temporary set of roots for the shoots of a clonal plant which it is desired to propagate. The actual grafting is done as close as possible to the root ball of the seedling understock. When the scion and the understock are well united, which takes at least a period from 6-8 weeks, the resulting grafted plant is planted deep enough to make sure that the place of union is well under the soil surface. This enables the scion to make its own roots, much as happens in a cutting. By and large, the sole reason for grafting rhododendrons is to supply this temporary set of roots. Since the introduction of hormones, as well as other advances in the techniques of rooting cuttings, it has become less necessary to graft rhododendrons. Even so at least in my experience of 30 years in propagating rhododendrons, there are still a number of good varieties, which require an excessively long time to root, or which usually give a rather low percentage of well rooted plants. Some varieties will root well one year and poorly another. In my opinion such varieties are more economically handled as grafts. Naturally every man must be his own judge, as to which method of propagation is the soundest for the variety in question. As to the livability of grafts versus cuttings, I have seen thousands of rhododendrons, originally grown from grafts, towering 20-30 feet, and still going strong. I doubt that there is a Rhododendron 'Mrs. C. S. Sargent', over 6 foot high, that wasn't originally grown from a graft, and any plant that size certainly didn't die in infancy. Here at Rhodo-Lake we grow most of our commercial varieties from cuttings, and we find that cutting-grown plants grow as well as grafted plants, especially after the second year.
For those who are curious about how we decide which varieties are to be grafted, and which are to be grown from cuttings, let me state this. We do not find it possible to use our propagating bench room much longer than 10 12 weeks for any one set of cuttings. Most of our cuttings are made as early as possible in the summer, mostly in July, and we try to get the rooted cut tings planted in cold frames by October 1st following. They are protected with shades and reed mats, and in the case of later plantings with sash as well. The cuttings re-root well during the late fall and early winter, and by spring we remove the mats and/or sash and allow normal growth to take place. This means that the large majority of the cuttings must be rooted in three months time. As a matter of fact we are able to get a good many out in a much shorter time, some as early as 8 weeks. This means that our propagating beds, heated to 70 degrees F., in the fall and winter, produce crops of either grafts or cuttings. If we grew nothing but Rhododendrons, possibly we might arrange to allow space to be occupied by the same batch of cuttings for 6-8 months. We have observed that when some cuttings are slow to root, re-sticking in a fresh batch of medium will accelerate the process and promote a better stand. I have no scientific explanation for this, but we have noted it repeatedly, and some day some inquisitive scientist will investigate, and come up with an explanation. Mr. Nearing in his article in the January 1957 Quarterly, seems to infer that growing things slow is the only good way. In nature things usually grow very slow, but any botanist will tell you that nature's way of propagating is not only slow but very wasteful. Only the very strongest survive and live to maturity. In the growing of plants for profit, something which almost all of us have to consider, the idea is to produce the most plant at the least expense. Time is money, even to the nurseryman, and if by reason of hormones, fertilizer, and the employment of all the refinements of propagating technique, he can produce a certain size and quality of plant faster and cheaper, competition will certainly force him to do so.
Mr. Nearing's statements in his article in the .January Quarterly regarding feeding of plants, are not shared by the great majority of reputable plant physiologists. I think there is no questioning the fact that green plants need feeding, and that they need nitrogen phosphorus, potash and a whole series of other elements. These substances should be present in every good soil, and their absence, or more likely, their unavailability will cause definite symptoms of malnutrition in Rhododendrons as well as in any other type of plant. Mr. Nearing states that "plants make their own food by combining air and water to form sugar, and this is the basis of all food." If this were true, then Rhododendrons could, at least theoretically, be grown in sterile sand, merely by supplying air and water to the roots. This premise has been proved false with all seed-bearing plants, including Rhododendrons.* An adequate supply of all chemical elements of the soil, properly balanced will supply any plant with the ingredients for good growth. The fact is, that chemical tests of plant tissues taken from healthy plants will show the presence of a number of elements, and conversely, tests on tissue from unhealthy plants will show the absence of one or more of these elements. When Rhododendrons or other plants are growing well without feeding, it is because there is ail ample supply of available nutrients in the soil. A virgin forest can reproduce itself only so long as no large amounts of timber or other products are removed. As old trees die and decompose, those elements present in their makeup, will return to the soil for absorption by the younger trees. When we bring in leaf mold and other partial or wholly decomposed plant material, we are once again supplying our plant beds with the same elements that were present in growing plants before they died, decomposed into leaf mold or other organic debris. Most nurseryman cannot obtain nearly enough of this organic material, since in our business we do not only remove the plants, but in many cases an earth ball as well. The aim of a good program of fertilization is to resupply the soil with such amounts of elements necessary to good plant growth, as are taken out by the removal of the produce of the soil, plus the deterioration caused by erosion, and other natural phenomenon. Regular cover-cropping of land, especially that used for the production of nursery stock, is essential to maintain a satisfactory organic content. Bad results from the application of chemical fertilizers has been promoted by slipshod ways of application, poor selection of formulas, etc. A complete soil test plus an evaluation of the mechanical state of the soil, and a knowledge of the requirements of the particular crop, will enable a good grower to estimate the amount and kind of fertilizer to apply. The method and frequency of application must be determined by the grower with an eye to the particular plant and his type of operation. The great danger, with plants as well as people and animals, is in feeding too much, too little, too often or too infrequently. Another thing to remember is that research in the nutrition of ornamentals is still in its infancy, and a long way behind the detailed knowledge we have of the requirements of some of our food plants.
I hope that nothing I have written here will he regarded as intended to disparage Mr. Nearing's extensive knowledge of Rhododendrons, or his accomplishments as a breeder. My aim has been to state those areas in which I definitely disagree with him. I am sure that there are even larger areas in the field of Rhododendron culture, on which our opinions would agree.
* Dr. R. P. While's work with "Rhododendron Nutrition" at Rutgers University, 1937.