A Discussion On the Merits of Grafting Rhododendrons
By Robert Bovee, Oswego, Oregon
The panel discussion on propagation held during the February Portland chapter meeting seems to have resulted in some misunderstandings. As reported in the April Bulletin of the American Rhododendron Society the consensus of opinion was "that a plant on its own roots was preferred to a grafted one because of suckering and sometimes that the understock is incompatible with the scion."
What seems to have actually happened is that a good many members left the meeting with the opinion that ALL plants should be on their own roots and that grafted rhododendrons were not good. It has only been during recent years that so many types of rhododendrons have been rooted. Most of the older collections contain many grafted plants. They are fine plants, many very large, and they win ribbons at our shows every year.
I would rather grow a plant that is on its own roots than a grafted one...providing the plant will grow and bloom well, but, some don't. That is why they must be grafted.
Some of our fine hybrids will not root at all, or not well enough to be propagated economically from cuttings. Others will root well one year and not at all the next year. Yet others will root fairly well but will not develop good root systems and some do not bloom well on their own roots.
You have probably heard, "plants with R. campylocarpum blood do not root well. There are one or two exceptions to this but most of the yellow hybrids must be grafted.
It is almost impossible to root R. 'Earl of Athlone' but we need that fine red. So grafted or no we grow it. My plant suckers a little but I am willing to spend five minutes a year in removing the suckers. Some years R. 'Purple Splendor' roots and some years it doesn't. We can't get along without that one, so we accept it grafted. I have two large plants growing side by side, one grafted and one on its own roots. They are equal in size, both grow and bloom well. I cannot tell one from the other.
A grower may root R. 'Britannia' one hundred per cent one year and the next not a cutting will root. Usually it seems to "strike" at least twenty-five per cent. It is also a difficult plant to graft. It does grow very well on its own roots. My five year old plant from a cutting is equal in size to a seven year old grafted plant but, in growth, habit and quality of bloom, I cannot tell one from the other.
R. 'Loderi', R. 'Naomi' and many others are usually grafted because they are difficult to root. It seems to be practically impossible to root R. 'Mrs. Furnival'. We need that wonderful rhododendron in our gardens, and so far as I know, it is always grafted and it is always scarce.
Last year I rooted a very small percentage of R. 'Diane'. These plants have not grown well on their own roots. Grafted plants of the same variety are big and husky. I have two six year old plants of R. 'Bow Bells'. One has never bloomed. The other has bloomed sparsely just once. They do not have good root balls. Three and four year old grafted plants of R. 'Bow Bells' are much finer in every way. Root systems are twice to three times as large, top growth is better...and they cover themselves with bloom.
New varieties are usually grafted. The grower has but a limited supply of propagating wood on a new plant and is usually not certain whether or not the wood will root. So, he plays safe and grafts. If, in this case, the grower did not propagate by grafting it would take many more years before new varieties would become available.
Sometimes understock is incompatible with the scion. But that is the problem of the propagator. He will discover that when he takes the plants out of his grafting bin. Few of such plants will ever reach you. No grower, who wants to stay in business, will supply plants which are not right.
We have all heard the statement that a plant on its own roots is more hardy than a grafted one. Is this true? I have never heard it proved. In my planting I have never lost a plant because of -its having been grafted. We hear occasionally of a plant breaking off at the graft under the weight of heavy winter shows. But this seems to be quite rare. I wonder if it happens to one plant in 10,000 or 20,000. When a plant is on its own roots it has a good chance of coming back if frozen down in winter. But where rhododendrons are grown we usually do not have winters of such severity.
I am neither for or against grafted plants. It seems to be that rhododendrons should be propagated in the best way to give good growth and pleasure. Most can be rooted from cuttings. A number must be grafted, or entirely eliminated from our gardens. As our knowledge of propagating grows more and more will be rooted. In the meantime propagating methods should not be a cause for worry by the home owner. Commercial growers are doing a good job of growing fine plants. Faulty planting methods are the real cause of most rhododendrons complaints by amateurs. We who have tried to answer the questions asked by the public at our local shows have found that to be true.
A method of propagating which has been given considerable national publicity during the past two years is the "mist" method of rooting cuttings. A complete greenhouse or a bench in the greenhouse is so arranged that cuttings are rooted under a constant mist of water. The publicity given this method in garden magazines and other publications, published in the eastern part of the country would indicate that this is a new method.
To the commercial growers in and around Portland this is by no means something new but well established procedure. The first grower to use this method in Portland, I have been told, has done so for six or eight years. He has a large greenhouse fitted with a mist system. Another grower built a similar greenhouse three years ago. Another was built last year. In addition other growers have especially designed rooms in their green houses fitted with mist systems.
To create the mist a pressure pump is connected into the water line supplying the greenhouse. Water is pumped through half-inch pipe and forced through very fine spray heads at high pressure. The spray comes out as an exceedingly fine mist, just like a heavy fog. These systems are operated sixteen hours a day. Plants root amazingly. Root balls are very large and cutting loss is low.
One grower would think he had a bad crop failure if he did not root at least 80% of his cuttings. And, the only reason for this low percentage is that each year some of the more difficult cuttings are put in with the hope that a good percentage will root. Another grower, recently told me, that he was this year using a mist system in connection with grafting plants. Over a thousand were under the mist and to date not one had been lost.
The procedure worked out here should work in other sections of the country. While plants are different the problems would probably be similar. Some plants would be quite easy to root and others difficult.
For those interested in research work there is always the problem of how to economically root name varieties of Exbury and Knaphill azaleas, and, how do you propagate an especially good variety of R. schlippenbachii ?
Air layering may be one answer but not from an economical standpoint. It still remains a mystery how to root a good percentage of R. 'Mrs. Furnival', R. 'Earl of Athlone', R. 'Purple Splendor', R. 'Britannia' and the yellow hybrids.