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Journal American Rhododendron Society

Current Editor:
Dr. Glen Jamieson ars.editor@gmail.com


Volume 9, Number 4
October 1955

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Rhododendrons Are Vanishing
By G. G. Nearing

        Though thousands of hybrid rhododendrons are propagated and sold every year, good specimens of the hardy varieties are becoming steadily rarer in northern New Jersey and neighboring regions. Many fine plants which were local landmarks have disappeared, and few suitable replacements are coming along.
        This tragic condition has two leading causes-first, the rake; second, the use of fertilizers and acidifiers. An incredible disregard of the special needs of rhododendrons and other ericaceous plants has lately overtaken the general gardening public, horticultural writers, commercial gardeners, and perhaps horticultural research centers. The rules for proper care have been known at least half a century and are exceedingly simple. Callous ignoring of these rules or substitution of new snap-judgment practices is wiping out our most beautiful of shrubs over a wide area.
        When a property changes hands, as it frequently does in our suburbs, the new owner almost immediately takes a rake, cleans out and burns all the leaf mulch from under the rhododendrons, azaleas, mountain laurels, Andromedas and similar plants. Death follows slowly but almost inevitably. Within a few weeks the density of their foliage is greatly reduced by shedding of the older leaves. Within months 'he lower branches begin to die. Once shapely specimens soon become so unsightly that within two or three years they are dug out and thrown away, while the owner mumbles something about his soil being unsuitable for rhododendrons.
        To make matters worse, hired gardeners do exactly the same thing and tell the owners that no mulch is need ed. They have a new method of covering the ground with an inch or so of peat moss and adding fertilizers. Peat moss, though an excellent soil component, is not a mulch. The roots grow up through it and are exposed to ruinous cold and heat. Fertilizers cause sappy growth, which kills back with the first hard frosts of autumn and may result in fatal bark-splitting.
        A mulch, to perform its most important function, must have air spaces for insulation. Two to three inches of oak leaves make an ideal mulch if they can be kept from blowing away. Other leaves also do well enough and in windy places can be anchored down with a dressing of pine needles, or with many small twigs scattered over the top. Grass clippings should not be used, because they become matted and sodden. Full length hay will do, but does not look well.
        Sawdust is not a mulch. If fifteen or twenty years old, it can be added to the soil in moderation and may be almost as good as peat. If fresh and un-weathered, it is ruinous to rhododendrons. Whether the wood chips now being used are any better, remains to be seen. They do furnish better air spaces, and if you can endure their unsightliness, they may prove better than no mulch at all.
        The feeding roots of rhododendrons are very delicate white threads produced in unbelievable quantity and very rapidly while the plant is in health. They occupy only the top three or four inches of soil under average conditions. Buried deeper, they gradually disappear, and new roots must be grown nearer the surface. A proper insulating mulch protects these feeding roots, and as decay reduces it gradually to a powdery mold, furnishes their food. Thus more mulch must be added every year.
        But as soon as the plant has stood three or four years properly mulched, it bends its lower branches to the ground, forming an unbroken dome of foliage. Its own old fallen leaves and tree-leaves blown in by the wind, lodge under it and are prevented from blowing away. No more mulching or other care is needed. The plant asks only total neglect. Given neglect, it will thrive. Given "care" it will probably die.
        Few owners of a fine plant can resist the temptation to fertilize it. Insidious advertising tells them that plants, like humans, must eat. This is not true at all. Plants make their own food by photosynthesis of water and air. To do this, they require very small quantities of certain substances, which for the most part are not used up, but remain in the dead leaves, to be reabsorbed by the roots in due time. No fertilizer is needed unless these dead parts are burned or otherwise destroyed, or unless living parts are removed (as for decoration or propagation), or unless you take a crop from the plants, as with farm crops, fruits or vegetables. The virgin forest was self sustaining. After countless thousands of years unfertilized, it contained a soil so rich that a hundred years of wasteful farming did not entirely deplete it. Rhododendrons come from the forest, and a mulch of forest leaves, as soon as it has remained on the ground undisturbed. for two or three years, supplies everything a rhododendron needs.
        Those who anyway cannot resist the urge to fertilize, should avoid any made-up fertilizers, especially shunning those recommended for rhododendrons or acid-soil plants, and for reasons explained in the next paragraph. Dexter's mixture, one part of salt petre (nitrate of potash) mixed with two parts of superphosphate, and scattered thinly over the mulch at the rate of about a trowel full to a three-foot plant, is probably safest. No fertilizer should ever be used in the north later than April. And especially avoid fertilizers which quickly give a deep green color to the leaves. A gradual deepening of color can be obtained without harm from a thin sprinkling of cottonseed meal.
        One of the worst aspects of fertilizing is the use of a chemical acidifier recommended by nearly all writers, incorporated in virtually all special rhododendron fertilizers, and sold without warning. Now, in order to avoid possible legal complications, I must state here that nothing hereinafter written about aluminum sulphate shall be considered a statement of provable fact. It is my personal opinion, founded on experience of many years and many thousands of plants killed. Not to prove before a jury that they died from the application of aluminum sulphate. would be next to impossible for reasons explained later. I believe that they did. but I do not. so state. A scorpion may have bitten them after the poisoning for all I know.
        A chemist said to me the other day. "Aluminum sulphate! Why would anyone put that on a rhododendron? It is the enemy of all life." So I suppose I can safely say that if a rhododendron was planted in pure aluminum sulphate it would soon die. If you reflect on the smarting sensation when you apply a styptic pencil to a razor cut on your chin, you will readily imagine what this raw alum does to the delicate roots of a rhododendron.
        What, then, is the lethal dose? Apparently it varies enormously with conditions of soil and drainage, and a very small quantity in a poorly drained soil might and probably does prove fatal in certain cases. Several years ago, at a lecture, I put the question to a professor from the institution where, I believe, the crazy idea of using aluminum sulphate on rhododendrons was first hatched, and he replied, as nearly as I can remember, in these words: "Yes, we know it is a poison, but if the subsoil is sufficiently porous, and if you water heavily so as to wash it out as fast as possible, it will not kill the plants." That, in my opinion, is the best that can be said for the use of aluminum sulphate.
        For a long time after aluminum sulphate has been applied, no harm appears to have been done. Months may pass with the plants looking entirely normal. Naturally it is hard to prove that what takes place after a period of months is in any way connected with the use of aluminum sulphate. To protect myself legally, I will not say that the following is caused by the aluminum sulphate. I will only state that in my experience it has followed the use of the chemical in cases too numerous to ignore.
        The new growth comes out a small fraction of its normal size. Subsequent growths are even smaller, until there is virtually no growth at all. Death may not follow for two or three years, or after a lapse of several seasons, the plant may even recover, but I am not sure that I have ever known a plant to recover after the leaves have dwindled to a tenth of normal size.
        Now let me relate my first experience with this poison. I built a sunken frame about 40 feet long and 5 feet wide, of cinder block plastered over with ordinary cement, and a bottom of cement and cinders about one to eight. In this I placed peat moss to a depth of about four inches, impregnated with a solution of about one pound of aluminum sulphate. That is, I used about a pound of aluminum sulphate to about 75 cubic feet. of peat moss, soaking it in slowly. This frame I filled with small potted plants, plunging the pots in the peat moss.
        Several months later, I was alarmed by wholesale deaths among the plants, with the dwindling growths mentioned above. I removed the plants to another frame, where thousands died, and as they perished, crystals of aluminum sulphate came out along the twigs like hoarfrost. I will not say the aluminum sulphate killed them, because I would be unable to prove in court that it did, but I will let my readers judge whether it did or not. I destroyed the impregnated peat, put fresh peat in the poison frame, and had plants thriving there for years afterward with hardly any deaths.
        I request that all who sell aluminum sulphate or fertilizers containing it, print on the package something like the following, wording: "Aluminum sulphate is a deadly poison to rhododendrons and other ericaceous plants, and should be used with extreme caution, as the lethal dose is not known." Please note again that I do not state this as a fact. It is merely the wording which I suggest vendors use on their packages pending further research. The chemical is now sold without warning.
        Naturally, the writers of books and magazine articles who have been recommending aluminum sulphate will be harder to convince than will the vendors. They will certainly try to defend what they have published. I can only ask each of them to buy a Rhododendron, paying a good price for it, and plant it with a heavy application of aluminum sulphate, then wait a year and report what happens. But I will ask them not to buy the plant from me. I have an affection for my plants.
        Aluminum sulphate does acidify the soil as claimed. So would nitric, carbolic, or other poisonous acids. Tannic acid is recommended for the purpose because it is non-poisonous in low concentrations. However, if a quantity of acid peat is dug into the soil before planting, it will nearly always furnish sufficient acidity. But do not use pure peat, as many growers in milder climates do, for it robs the plants of their hardiness. Once established in peat, the roots will not grow from it into the soil, but remain for years in the peat ball. Peat stays frozen longer than most substances, and the frost action on the roots contained in it is often disastrous. Use at least as much soil as peat, and mix the two thoroughly.
        If through some emergency it is necessary to use a chemical acidifier, the most convenient is sulphur. Alkaline in itself. it is quickly acted upon by bacteria, which convert it into fairly safe acids. Not only safer than aluminum sulphate, sulphur is also more efficient and cheaper, though a little slower in its initial action. But even sulphur must be used with caution. A thin sprinkling goes a long way.
        Not only should fertilizers be avoided, especially newly concocted ones, but most sprays are dangerous. After a disastrous experience with one of the newer sprays, I limit myself to home-mixed Bordeaux 2-2-50 or weaker, arsenate of lead, and nicotine sulphate, using always more caution than spray, and never spraying while the sun shines.
        Listen to everybody's advice, but be exceedingly wary about following it. Nearly all my disasters have resulted from advice taken from experts. There are countless experts, some of whom actually have knowledge, while others are paid to recommend something profitable for its manufacturers. A rhododendron thirty or forty years old and in prime condition is so valuable and so difficult to replace, that unless some urgent need arises, nothing should be used on it except mulch, water, and large quantities of good sense.


Volume 9, Number 4
October 1955

DLA Ejournal Home | QBARS Home | Table of Contents for this issue | Search JARS and other ejournals