QBARS - v28n3 Rhododendron Cuttings

Rhododendron Cuttings
Dave Goheen, Camas, Washington
Reprinted from Portland Chapter Newsletter

From almost the beginnings of organized agriculture, people have realized that a quick and convenient method of producing additional plants from existing plants could be accomplished by the practice of slipping or, as we say today, the rooting of cuttings. At first this method was carried on in a hit or miss fashion and was very empirical. Some plants rooted easily, whereas others rooted with great difficulty or not at all.

For years, the mechanism of the process was not understood and it was practiced as a sort of "black magic" type art. Unfortunately for rhododendron fanciers, their plants proved to be among those whose cuttings rooted with much difficulty! Thus, for years the standard methods of producing additional plants from superior rhododendrons took the form of either of two methods. both laborious and time consuming. These were grafting in which the cambium layers of the cutting and an understock are matched and held together in some fashion and layering in which a low branch of a bush or tree. particularly if it contains a node, is buried under the ground while still attached to the main stem.

Fortunately, biochemists and agronomists began to study the problem and from their endeavors have come the realization of what is required for a bare stem cutting to produce rootlets and eventually a new plant individual. The process is controlled by a series of chemicals called auxins . These materials have the property of causing certain cells of the cambium layers of living stems to alter and first form a callus or group of proto-root cells which under conditions of sufficient aeration and warmth, rapidly generate root masses and cause formation of surprisingly large root balls in relatively short time periods Thus, the presence of absence of these auxins controls the chances of rooting and allowing the cutting to survive and prosper before it uses up its nutrients.

Chemists have found that the auxins are surprisingly, relatively simple chemical compounds. One of them, for instance, is composed of a compound of carbolic acid with acetic acid, the material that gives vinegar its sharp odor. Others have been found to be breakdown products of certain amino acids found in proteins. The important thing is that the auxins are relatively easy to synthesize and, as a result, are readily available for use in the propagation of cuttings. There are several mixtures available for use. All contain small amounts of the auxins either as dilute solutions or as dilute mixtures in powder such as talc. Most of the proprietary formulations also contain a fungicide to help prevent deterioration of the cutting before it can callus and root. I find the use of powders quite simple. One such formulation is called Hormodin and consists of a package of three bottles each containing a powder with 0.1%, 0.3% and 0.8% indole butyric acid. Cuttings are treated by wounding and dipping into the powders. Cuttings. such as those from easily rooted lepidotes, use the low concentrations, whereas the more difficult elepidote hybrids require the more concentrated powder. Many people prefer to use liquid solutions and soak the wounded cuttings in various solution strengths for various lengths of time. Both methods are entirely suitable and greatly enhance the probability of obtaining roots on cuttings kept under moist conditions. It must be remembered that the roots don't form immediately and thus the cutting must be kept from drying out as very little moisture can be drawn up the stem until the rootlets form.

It is a matter of considerable interest that Chinese farmers knew for more than a thousand years that the urine from domestic livestock had the ability to aid rooting. They didn't know why but it worked. We now know why. The reason is that one of the most powerful auxins is found in cow's urine. It is the same material as the active principle of Hormodin, indole butyric acid. Ironically, the Chinese used it for centuries without knowing what it was, whereas our Western agronomists have only discovered its use in the last 20 years or so!