Rhododendron Rootstock
A. R. Heineman
It will be perfectly in order for me to admit that I am a rank amateur when it comes to the growing of rhododendron. Just * a little over four years ago we migrated to this grand Northwest, and that is when we saw our first rhododendron in bloom. It was a 'Pink Pearl'. It would be interesting had it been possible to register our emotions as we stood before this beautiful thing. We then and there resolved if we would ever own anything up here it would be a rhododendron.
The very nature of the plant gripped my imagination at the outset. The unique way it grew its leaves, in clumps or whorls, at the tips of the stems. It was so different from anything that I was used to. I wondered what the nature of its root system might be, whether of a taproot or fibrous root. Because of some very costly experiences that I have had, and seen, due to certain fungus diseases that attack plants of the taproot generic, I gathered up all possible literature on rhododendron, and ere long I was involved in quite a little project. Wild plants, natives, that I inspected were of taproot nature. Plants that I purchased from local nurserymen seemed entirely fibrous rooted. This is interesting how the plant transforms its nature. Likely most advantageous for all of us, few it makes transplanting easy, and makes the plant most amenable to management. The deeper I got into the matter, the more plants I seemed to need. Soon I learned of finer one.; and still finer ones, and naturally enough we had to have some of them too.
In the spring of '47 we purchased quite a number of what was supposedly "The finest." Being familiar with nursery stock I found occasion to question the nurseryman on the character and nature of the under-stock he had used. I noted that in a number of cases they were grafted at the very tip of the understock, also, that it looked gnarled, rough, and lacked that smoothness that represents vigor. Being assured that it was first class, wanting the particular varieties, knowing that if they would grow I could grow them - they were accepted. Today a number of them have died more of them will die. In some cases the bud-stock has greatly overgrown the understock forming a distinct "bottleneck" condition. Where the graft is some inches above ground level and over grows the root stock they are difficult to maintain in an upright position. Where it is the reverse the graft breaks off. Where it happened that the graft was not any more vigorous than the root they have maintained themselves but lack a great deal in making a plant. Their neighbors of similar material on good root-stock have trebled in size. On examining the root-stock on the failures, as well as near failures, I find that the root-ball is but little, if any, larger than it was when first planted. In most cases the roots are all on one side of the stem, much like a layer. Also, the terminal tip of the rooted portion of the stem comes to an abrupt end as though it might have been torn off from another plant. This is not the condition of a normal seedling root development. I can not help but wonder how well the influence of understock on rhododendron is understood. I believe that it is deserving of some study and consideration. Not alone how it influence growth, flower and color, but I believe that it has a fixed relation to hardiness. The past winter ('48-'49) produced some outstanding results. Regardless of the hardiness rating of a variety; if the plant had made good growth which it will only do with a good root system, it came thru in good condition. And when spring came it started into good growth and carried on, while those of poor root-stock had a miserable time of it.
If your plant is not performing well do not hesitate to take it up, examine the root ball. It should have countless numbers of fine white roots protruding in all directions. If it hasn't, get someone with experience to help you, there is something very definitely wrong without these fine rootlets. We are dealing with a very beautiful thing in the rhododendron. Let us work together to develop it to its fullest fruition.