Some Observations on Rhododendrons in the South
J. Harold Clarke
During September and October of 1953, Mrs. Clarke and I had an opportunity to visit rhododendron growers on a trip through the South. Actually. we did not find very many rhododendron growers, nor very many cultivated rhododendrons, but there were a few plantings and what we saw impressed certain things on our minds about the culture and the possibilities of this particular group of plants in the South. The principal reason for putting our observations on paper is to stimulate thinking on the part of those who might like to grow rhododendrons under rather hot, dry conditions.
Our story begins at Richmond, Virginia, in the garden of Dr. Thomas F. Wheeldon who has made remarkable progress in assembling a collection of Azaleas. On the grounds of his beautiful home he has assembled over 1500 species and varieties of azaleas, probably the finest private collection in the United States, if not in the world. He has only a few varieties of rhododendrons at the present time but most of his plants looked quite happy and contented in spite of the fact that they had experienced twenty-one consecutive days this past summer when the temperature reached record highs. Of these twenty-one days, ten consecutive days saw the mercury climb to more than 100°. We have frequently heard it said that the reason rhododendrons do not do well in the South is because of the high temperatures. Certainly this was a test summer if there ever was one. In spite of it, the rhododendrons were growing nicely. How was it done? The methods used by Dr. Wheeldon probably point up in very concise form the rhododendron problem in the South and methods of solving it. These methods were comparatively simple but extremely important. In the first place, the soil was deeply prepared with peat moss and leaf mold worked in to a depth of several inches. After the plants were set. they were rather deeply mulched with peanut hulls. This material makes an excellent mulch but others, such as sawdust, would probably have done as well. During the extreme heat, the irrigation system was used freely so that the plants never suffered for lack of water. Most of the plants were in semi-shade but some of them were in almost full sun. I do not recall the original pH of the soil in Dr. Wheeldon's garden. However, he has been using Ammonium Sulfate, which tends to increase acidity, as a source of nitrogen. He has also used a large amount of iron sequestrene, one of the new chelated forms, which will remain available to plants much longer than other forms of iron. After such heat, I confidently expected to find many of the leaves scorched and burned. However, that was not the case and under the conditions in Dr. Wheeldon's garden, the rhododendrons seemed to have withstood the heat as well as the azaleas.
Some Successful Plantings in North Carolina
In North Carolina we visited several of the larger cities and talked to nurserymen and others. Some of the nurserymen simply stated that rhododendrons would not grow in that area because of climatic conditions. However, a few took the other viewpoint and stated that rhododendrons could be grown quite satisfactorily once people set themselves to doing it. In Greensboro we had the pleasure of seeing some very fine rhododendrons at the home of Mr. Aubrey Brooks. These had been planted some twenty-three years ago in holes which had been dynamited out. Oak leaf mold and other organic matter had been worked into the soil and now the plants, some six to seven feet high, look as good or better than azaleas growing around the same home. These plants had been under the watchful eye of the local nurseryman who had planted them and who had added acidifying material around the bushes whenever they began to look chlorotic.
At Charlotte, North Carolina. we found considerable interest in rhododendrons, and a few plants growing there. The soil in some gardens was reddish clay with rather poor drainage and having a pH of about 7. Such soil will undoubtedly require, for successful rhododendron culture, the installation of good drainage as well as acidification. If tile drainage is used. or if sand or gravel can be worked in deeply enough to provide good drainage, together with peat moss, leaf mold, or other similar material, the acidification problem will he simplified. Whether or not enough acidification can be obtained with ammonium sulfate, I am not sure; possibly it will be necessary to use sulphur in addition.
Effect of the Native Rhododendrons
On the Blue Ridge parkway going into Asheville, North Carolina, we went through thousands of acres where native rhododendron, are growing in heavy stands. This area has been the source of many plants dug in the wild and shipped to northern markets. Certainly these native rhododendrons. maximum, catawbiense, and some carolinianum, do very well on the higher hills and mountains. One might think that the presence of these many very lovely wild rhododendrons would greatly stimulate interest in the hybrids. However, I am not so sure but what it has worked the other way. In the first place, many people have gone into the woods to collect wild rhododendrons with very poor results. They have tried to take fairly large plants without being able to get a good root ball and so many of these collected plants have lived for a year or two and then died. Their death, in some cases, has been blamed on soil and climatic conditions rather than on the fact that a poor job of digging and transplanting has been done. This has given the whole rhododendron group the name of being unsuited to local conditions. Furthermore, the flower color of most of these native rhododendrons is not very exciting when seen on a single specimen growing in the home garden; not nearly so effective as when seen covering a whole mountainside. Accordingly, many local people have apparently come to the conclusion that the best place for rhododendrons is in their native habitat and that they will enjoy them by driving up into the mountains to see them. This is probably a very good conclusion as it is somewhat difficult to get a nice specimen plant growing from collected material. This rather adverse effect of the native rhododendron, I believe, has extended for quite a distance in the southeastern part of the country.
Just south of Asheville is located the famous Biltmore Estate where there is a fabulous collection of azaleas, several thousand of the native azaleas collected in the southeast together with a correspondingly large number of cultivated varieties brought in from all over the world. There are just a few rhododendrons here, just enough to indicate that they will grow well in this area if given reasonable care. Some of the best are rhododendrons of the fortunei type which had come from Mr. Dexter of Sandwich, Massachusetts. These plants were making a very nice growth, even by standards of rhododendron culture in what are considered to be favorable areas. As thousands of people visit this Estate each year to see the azalea display and the other garden attractions, it would he a fine thing if the rhododendron collection could be increased.
One of the interesting things at Biltmore was R. chapmanii from Florida. Many people in the South commented that all of our rhododendron hybrids have been bred for other localities and that it is too bad there are not some breeders in the South who can produce varieties especially adapted to their conditions. Possibly R. chapmanii might be a good place to start, as it might provide that needed adaptability to Southern conditions.
Considerable Interest Around Atlanta
In the Atlanta, Georgia, area conditions seem to be a little more favorable for rhododendrons than in some other parts of the South. Some nurserymen are already handling a few hybrid rhododendrons and speak well of the possibilities in that general area.
Near Chipley, Georgia. the Ida Cason Gardens development is planning to include a fairly large collection of rhododendron varieties. Many of the native azaleas have already been established and more will be added. Several artificial lakes have been made which will offer ideal conditions for azaleas around their shorelines. This area, being developed for public recreational use with small admission fees, is visited by thousands of people each year and as the gardens develop. the numbers will undoubtedly increase. It is hard to imagine a better place for rhododendrons to be brought before the public eye in the Southeast.
As we went west through Alabama. Mississippi, and on to Dallas and Fort Worth, Texas, the story, in general. was the same. There are practically no rhododendrons being grown but now and then some venturesome soul has set out a few plants and is beginning to learn about them. Nurserymen are interested to some extent but many of them have never handled any rhododendron plants at all. The very few plantings of hybrid rhododendrons made in the past, in many cases have survived for a short period and then have died out. The indications are that this lack of success has been due more to lack of proper care than to anything else.
In summing up general impressions of the South as a place to grove rhododendrons, it would seem that many hybrid varieties can he expected to grow reasonably well under condition to be found in many areas. It will certainly he essential to prepare the soil well with peat moss, leaf mold. sawdust, or what-not. Incidentally, we saw on one day no less than four large piles of sawdust being burned at sawmills as a means of getting rid of it. It will be necessary to check the pH and possibly in some cases to add sulphur. In other cases, sufficient iron may not be readily available and something like iron sequestrene may he useful. It will be most important to get good drainage. This may mean additional water will be required during the summer but it will be important to provide ample water during the summer anyway. A little more drainage in the soil will probably not make very much difference in the water requirements. The use of a mulch is apparently very necessary. This will help keep down weeds and eliminate cultivation or hoeing which the shallow-rooted rhododendrons do not relish. It will help to hold the moisture supply at a more uniform level, although it will certainly not take the place of summer watering, it will simply make watering necessary less frequently and will prevent the rapid drying out and re-soaking which necessarily occurs when un-mulched soil is kept irrigated for plant growth. Shade probably will be necessary for most varieties although some will undoubtedly stand the sun just as well as will azaleas. However, deep shade is questionable. A lath house would be ideal, as would the north side of a building. Plants can be set on the north side of tall trees to provide shade but the plants should be far enough away so that they will not be starved by competition with the tree roots. At one place in Alabama we saw a very nice bed which had been prepared under trees for some special azaleas. The tree roots invaded this bed to such an extent that they practically filled it and choked out the plants which it had been made to accommodate. This means that where rhododendrons are to be grown under trees in an area where water and plant food are scarce, there will be a constant battle to keep the tree roots from filling completely the soil specially prepared for the rhododendrons. It may mean watering and feeding the trees more than has been done in the past so that they will not he so greatly in need of water and plant food.
In most of the South, fertilizer will probably have to be used rather freely. The thing to watch with rhododendrons will be to use types of fertilizer which leave acid residues in the soil and not ones which leave lime deposits. Rhododendrons require ample plant food, and gardeners will have to experiment, under their own conditions to see just how much fertilizer they should apply to benefit the rhododendrons without causing damage. In order to lessen danger of winter injury, the plants should not be stimulated in late summer.
One thing which would further the rhododendron cause in the South a great deal would be a local botanic garden, arboretum, or public park where rhododendrons could be properly grown and where varieties could be tried out on a rather extensive scale for their adaptation to the South. Of the hundreds of varieties available, there are undoubtedly many which will do well in the South and many which will just not be happy there under any conditions. For the small grower to try out any great number is impractical but if a botanic garden could do it properly, it would lie a real service to gardening in the South.