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Journal American Rhododendron Society

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Dr. Glen Jamieson ars.editor@gmail.com


Volume 6, Number 4
October 1952

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Some Trends in the Development of the Knap Hill Azaleas
J. Harold Clarke

        There has been considerable interest during the past two or three years in the so-called Knap Hill group of azaleas. Until about five years ago little was heard about this group and so far as the writer knows, plants were not being listed by any American nurseries or shown in any of the Shows in this country. This is rather surprising when we consider that the first steps in the production of these varieties occurred many years ago although the first ones which were propagated individually and sold as clones were introduced about 1925.
        Preliminary work in breeding for this type actually began about one hundred years ago when the elder Anthony Waterer began his long period of rhododendron and azalea improvement. One of the important steps which sets this group of hybrids off from most other azalea groups was the introduction of R. occidentale into certain crosses made by Anthony Waterer about 1874. G. Donald Waterer in the January 14, 1950, issue of the ARS Quarterly Bulletin outlines the development of the type at Knap Hill.
        Probably one reason why such an outstanding group as this was not observed by Americans and introduced many years earlier is that the plants are rather difficult to propagate. They can he grown by layering which gives good plants eventually but is slow and expensive. Some of the varieties root fairly readily from cuttings but there is usually great difficulty in getting them to grow on the following Spring.
        The younger Anthony Waterer at the Knap Hill Nurseries followed the practice of raising seedlings from the best of each year's group of seedlings, hence the parentage became exceedingly involved. It is said that the elder Anthony Waterer made few notes of his crosses and that he seldom increased any one plant vegetatively, preferring to sell mixed seedlings. This may be one reason why these plants did not come to this country sooner since nurserymen would be less likely to import un-named seedlings.
        After the Knap Hill hybrids had been developed for some time, certain plants were obtained by Slocock's Nursery, by Mr. Lionel de Rothschild of Exbury, and by the late Edgar Stead at the Ilam Estate at Christ Church, New Zealand. Each of these have continued the breeding work and so now we have the Knap Hill varieties from the Knap Hill Nursery, from Slocock's, from Exbury, and we understand that some of the so-called Ilam varieties are now being grown in this country.
        The difficulty of propagating these varieties has led to certain developments which are really the basis for the writing of this article, and which should be understood by those who are interested in obtaining them. It has been stated authoratively that some of the varieties have been introduced as groups rather than clones. This would correspond to the British custom of naming certain group varieties although with rhododendrons such names have been given to. offspring of crosses between species or between species and hybrids. Certainly there seems to be little justification for the giving of such group names to any of these azaleas which have such a varied background. Some English breeders have been selling seed of certain varieties. Most American growers who purchase such seed undoubtedly know that the seedlings will vary considerably and that the name of the parents should not he used to designate the offspring except by indicating that these seedlings are from open pollinated seed of a certain variety. Certainly there is no justification for using the name of the female parent to apply directly to any of the offspring.
        Certain nurseries in England are said to have informed American customers that some of these varieties come so true from seed that it is no longer necessary to propagate asexually and so they plan to sell only seedlings. Presumably they would make some selection and discard the poorer seedlings. However, this poses a problem to American customers. It would seem to this writer that the selling of seedlings would be perfectly justifiable where every customer can come to the nursery and select the plants he wants, but it would be quite a different problem to fill mail orders. Where a variety is propagated asexually as a clone, anyone can order that variety and, barring mixtures, be sure of what he is getting. If he orders from a group of seedlings, whether they have bloomed or not, he is not very sure of what he is getting unless the nurseryman takes the trouble to make a specific description of each individual seedling which he is going to ship which, of course, he could not afford to do.
        It may he that some of these varieties come practically true to type. However. the Knap Hill group in general has been developing over a period of about a hundred years with a tremendous number of different crosses being made, most of which have never been definitely recorded. There is pretty good evidence that the following species have all been involved in the parentage of this group: R. calendulaceum, japonicum, molle, speciosum, viscosum, nudiflorum, luteum, arborescens, roseum, and occidentale. It is hard to see how any horticultural variety with six or eight or ten species in its ancestry could come anyway near true to type from seed.
        The writer this year bloomed some two or three hundred open pollinated seedlings of some of the Knap Hill varieties and found extreme variation. It is true that the average run of these seedlings was very good so that most of them could be sold as good garden plants. However, it would be difficult to find any two plants which were nearly identical. This, of course, is to the plant breeder's advantage because where there is variation there is always a chance to select out superior types. It is also fine for the local customer who can pick out unusual individual plants which fit his particular requirements. It would seem difficult, however, to send these wholesale to other nurseries, or by mail order, except as "mixed seedlings" of the Knap Hill type.
        Therefore, there would still seem to be a very important place for the asexual propagation of the present named varieties, at least the better ones, together with the best of the seedlings which are being grown by various breeders. There is little doubt but what the general excellence of the seedlings will result in the naming and introduction of a large number of new varieties. Undoubtedly many will be named and introduced which should not have been named, yet in the process we can look forward to the range of blooming season so long that we can have quite a good many new varieties without too much duplication.
        "How are these going to be propagated?" Certainly the American nurseryman is too impatient to rely very much on layering, and the grafting of this type of azalea has not been very satisfactory. Therefore, growing by cuttings appears to he the only practical method for large scale production. Admittedly such propagation up to this point has been unsatisfactory. However, it is probable that with special care as to the time of taking cuttings, using the proper root-inducing hormones, together with other special methods, a reasonably rapid propagation may be developed. Furthermore, as new varieties are selected some of them will undoubtedly grow from cuttings much more readily than others. Such varieties will he propagated in preference to the others and probably used as parents so that conceivably we may eventually have a number of varieties which can be grown from cuttings with reasonable success.
        It is beyond the field of this article to attempt to give a definite description of the Knap Hill group. They are extremely variable and deciduous, some resembling the mollis hybrids fairly closely and some resembling R. occidentale. However, most of them are unlike anything we have had in the well known azalea groups, especially with respect to their large flowers and unusual range of colors.
        It is to be hoped that breeders will be very careful in naming and distributing new varieties. Certainly we do not want to get into the same situation that exists in connection with a number of the English rhododendron varieties. In other words, all future varieties named, in this country at least, should certainly be clones and not groups. Nurserymen who do handle any "group" varieties and know it, certainly should so specify in their catalogs.
        We may look forward to a great number of seedlings of the Knap Hill type appearing on the market in this country. That is all to the good in some ways but the discriminating buyer will stick to the named varieties unless he can actually see the seedlings before he buys them.


Volume 6, Number 4
October 1952

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