QBARS - v18n2 More About Rhododendrons in Southern Red Clay

More About Rhododendrons in Southern Red Clay
Chas. A. Dewey, Jr., Charlotte, N.C.

Surely no one will argue with the statement that a failure is often associated with an "unawareness" or "underestimation" of the pertinent facts involved in an undertaking of any kind. Fortunately, the frequent failures of rhododendron plantings in Southern "Red Clay" is, in my opinion, no exception to this rule. I believe that when we here become aware of the likes and dislikes of these fine shrubs, then, and only then, will we succeed. Many who should know better, still claim that "rhododendrons will not grow here." I believe that the fault lies not with the rhododendrons but with a general misunderstanding of the culture of rhododendrons.
Not so many years ago, the cultural requirements of azaleas (Kurume and Indica, principally) and camellias were not generally understood, consequently the culture of these fine shrubs was left to "specialists." Today, it is a different story; the cultural requirements of azaleas and camellias are generally well known, so well known, in fact, that even a neophyte can expect, and realize, success. But only if the neophyte, or inexperienced gardener, plants his azaleas "right." In planting an azalea "right," the gardener may not realize that he is rather closely observing the "likes and dislikes" of the azalea, but of course he really is.

Azalea Problems Being Solved
In our area, the culture of azaleas and camellias offered a rewarding challenge and still does, but now this challenge has been pretty well conquered. This achievement, in my opinion, leads directly to rhododendrons. I believe that we will find our present knowledge to be of tremendous value in "getting to know" rhododendrons.
In the October 15, 1958, Bulletin of the American Rhododendron Society (Vol. 12, No. 4), 1 presented an article entitled "Some Experiences with Rhododendrons in Southern Red Clay." My 1958 article was presented in the light of a progress report. I sincerely hope that this present article will convey the same impression, because it is also presented in the same light. There is much to be learned about the culture of rhododendrons in our area, but in our immediate vicinity much has been learned during the last few years. As for our own experiences in, and around Charlotte, I believe that we have learned the following prime considerations during the past twelve years:

Good Drainage Required
1) Above all, rhododendrons require good drainage and the aeration resulting from this sometimes elusive situation. To achieve good drainage requires some thought, because what is good drainage for an azalea might be intolerable for a rhododendron. By planting our rhododendrons in raised beds, we have practically solved this problem. Here, I believe, that rhododendrons should be planted more "on the ground" than "in it." In 1958, I first reported some success with this method, and now feel more confidently than ever that this is one key to success in our area with rhododendrons.
It has been my experience that any rhododendron planted with its root ball one to two inches below the soil level will die. Unfortunately, this planting technique is one rather widely practiced here, and certainly is responsible for some of the poor experiences with rhododendrons in our soils.

Partial Shade
2) Rhododendrons will usually do well in any site where azaleas and camellias are doing well. This is usually in partial shade, in an area protected from strong winds. I have learned to avoid planting rhododendrons in dark, shady, damp glens. This is because in our area of heavy soils and high summer, temperatures the "trouble causing" fungi seem to be most prevalent in deep shade. Rhododendrons need a good deal of sun to stay healthy and bloom well. I am amazed at how much sun some rhododendrons seem to withstand and even enjoy: however, they should be given protection from strong winds. It is easy to provide a suitable windbreak by using several of any of the long list of handsome broad leaf evergreens which do well in our gardens.

The Planting Medium
3) A planting medium must be prepared using generous amounts of leaf mould, peat moss, or saw dust with some sand or horticultural perlite. Preparing a planting medium is nothing new down here. We need to do this in order to succeed with most any of our better shrubs. It is new, however, that this medium should be about 60% organic material, only about 30% local soil and about 10% sand or perlite. It is new also that, if saw dust is used, approximately one-quarter of one pint of ammonium sulphate should be added per bushel of saw dust. Do not use any aluminum sulphate, insist upon your supplier furnishing ammonium sulphate. It pays to be "hard headed" about this item. Even with peat moss or leaf mould, I like to use about one quarter of a cup of ammonium sulphate per plant when preparing a raised bed several feet in diameter. The ammonium sulphate seems to always provide the acidity and nitrogen required in initial planting. I usually prepare the planting medium right on the site. For example, let us consider the preparation of a typical planting site:
a) Usually, I will dig a hole about three feet in diameter and about 12 inches deep, setting well aside one-half of the soil removed. The soil set aside will be used in the planting medium.
b) With the volume of soil set aside, I will thoroughly mix the organic matter required, the ammonium sulphate and the sand or perlite. In this instance, the volume of soil set aside is around three bushels to which I would add about six bushels of organic material plus approximately one gallon of sand or perlite per bushel of organic material. Of course, I would also add the desired ammonium sulphate and then mix the entire batch thoroughly being certain that the soil in the mixture is pulverized.
c) I now have considerably more mixture than is required to fill the hole and I use the excess medium to form a Raised Bed, or "Cucumber Hill" about six inches above ground level. The rhododendron to be planted is then placed within this raised bed with the top of the root ball just barely covered. Usually this will mean that the bottom of the root ball will be near ground level, or only several inches below the original site level. I usually remove the burlap prior to planting although I do not know that this is necessary. The customary practices observed to insure firming the soil around the root ball and subsequent watering should be practiced.
d) Having planted the rhododendron, it should be mulched. Pine needles, oak leaves, bark from saw mills, or chopped tree trimmings all make excellent mulches. Undoubtedly there are other fine materials which will readily permit the flow of water and air. A mulch which is dense and heavy, or encourages stem rooting, increases the likelihood of disease, in my opinion.

Don't Over Fertilize
4) As for care of rhododendrons, I'd suggest treating them about the same as one treats azaleas and camellias. I would, however, suggest that no chemicals be used unless there appears to be a real need. In my opinion, I would "go very lightly" on the use of fertilizers. I for one have not found any chemicals yet which will successfully compensate for poor initial planting. If a plant does not look well, review the planting and exposure. More than likely, you will find some error in planting or exposure. But then too, every now and then, a rhododendron will just die. Most of us have had camellias do the same thing. Properly planted, I believe that rhododendrons are relatively maintenance free.
5) In grouping rhododendrons, or bedding, we usually plant each rhododendron as though it were alone. This practice not only eliminates extensive bed preparation, but tends to improve drainage around each plant. The entire grouping is then mulched which, if maintained, completely hides the "local" raised bed at the base of each plant. Sometimes, the bed is outlined with logs, or stones, which serve as a mulch container or retaining curb. If this curb is kept at a reasonable height, the mulch will spill over and hide it, however, some feel that such a boundary enhances the beauty of the planting.
6) Water plants well during the first spring. Once root balls dry out, and they dry quickly when first planted, they are rather difficult to wet thoroughly. I like to keep my plants well watered until early summer during their first year and then reduce the rate of watering. Too much watering during the late summer months and during early fall tends to cause halfhearted fall flowering and retards dormancy. I also believe that if plants are kept too wet during very hot months, destructive root fungi will be more prevalent. I prefer to keep my plants rather dry during July, August and September while soil temperatures are very high. Properly planted, in a good site, the rhododendrons should not required any watering the second year except in cases of drought. In the third year, I suggest they be left alone.

My comments above are certainly not the only way to succeed with rhododendrons in this area. I know of rhododendrons growing well here in pure peat moss, and of another, large group growing in leaf mould alone; however, in each instance, raised beds are used. Our knowledge is increasing steadily. The more we learn, the more convinced I become that rhododendrons will have a more important place in the future of our gardens.