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Experiences In Rose Hybridizing

Reprinted from The Australian Rose Annual, 1969

By Herbert C. Swim, California, D.S.A.

I wish to make it quite clear at the outset that I make no claim to any original discovery from my experiences in the hybridizing of roses. I would like to discuss them only because they seem, from my point of view, to have been the most useful of the many observations made over the years.

In looking back, it seems to me that among the most significant of my early realizations was one that made itself apparent after a series of frustrating experiences which ended in failure.

My first experiences in the making of exploratory rose crosses, while not entirely failures, were sufficiently such as to make it appear expedient to evaluate the factors involved in these failures and further to try to place some priority on these or, in other words, give them a rating as to importance.

For my own use an apt title for this procedure is “A Priority of Limiting Factors.”

I shall try to illustrate what I mean by using some actual experiences and relating them in the approximate order of their influence on the success or failure of a given objective. It seems to me that the clearest way to do this is to name a problem and then proceed to discuss it.

Vigour. I noticed in my first years of hybridizing that many of the families of seedlings were disappointingly lacking in vigour to the extent that often as few as 10% of a family were vigorous enough to be acceptable on this basis alone. In the early stages of any plant-breeding programme one must do some close inbreeding in order to explore the inheritance traits of the prospective parents, and it naturally followed that there were a number of such populations (families) in my early crossings. I noted that almost without exception these seedlings displayed a major regression in vigour. I soon discovered also that this result could be predicted with a high degree of accuracy. Beyond this, however, I discovered that unless I was very careful to use parents that were not only distantly removed from one another in origin, but had more than ordinary vigour in themselves. I could again expect no more than a small proportion of the resulting offspring to be acceptable in vigour.

Flower petallage. As a result of selfing (using the same cultivar for both seed and pollen parent) I discovered in the early years that the single petalled cultivars bred completely true to this trait; in other words, all singles when crossed with singles (providing they had no petal aids) gave only single petalled offsprings.  Since there are, of course, a great many levels of petallage in rose cultivars, it would seem probable that the inheritance of the quantity of petals may be due to a complex of factors. Be that as it may, it became apparent that a generality in this area could be made with a reasonable degree of accuracy. If the breeder were expecting or desiring rose progeny with double flowers, he had best make sure that any semi-double cultivar he used as the parent be complemented by another parent that had a good degree of doubleness - not necessarily fully double, but at least adequately so. I discovered that if one fails to do this, very few of the progeny will be acceptable in quantity of petallage - again a “limiting” factor.

Mildew Resistance. This quality, together with the next two, rank about equally in the degree to which they limit the breeder to selecting parents with an acceptable level of each given quality. It is generally felt among the rose breeders to whom I have talked that this quality is a dominant one which covers up the alternative quality, mildew susceptibility, when both are present in a given cultivar or seedling. 

Unfortunately, the wild roses that formed the basis for much of the early breeding work, particularly in the larger flowered cultivars, have a fairly substantial degree of susceptibility to mildew.  As a result we have very few garden cuItivars today that can be considered immune or nearly immune to mildew. 

This inevitably means that in our eager search for advance or novelty with respect to the flower qualities of our larger-flowered garden roses, we are working with parents on both sides with at least some degree of susceptibility to mildew. This means that we will produce very little that is more desirable than either parent, and with most of the seedlings being only equal or somewhat worse than the better parent with respect to this quality. Here, again, if we find it expedient to use a parent cultivar with some susceptibility to mildew, then we would be wise to use a mate for it that has a corresponding resistance to the same disease. Otherwise, our resulting offspring will be useless because of their susceptibility to this disease. I am glad to report that in this field some very fine progress is being made by various breeders, and I am confident that in the next decade or so we shall see some substantial progress, especially in resistance to powdery mildew. 

Flower Form. I would incorporate in this category the form of the bud also. The rosarian of today seems to like most of his flowers to be regular in form, in spite of the fact that the classic rose is very informal in the arrangement of the petals. Perhaps the rather globular buds and informal open blooms of yesteryear’s roses are the more natural form-pattern for the flowers of this great plant. Be that as it may, the rosarians of today seem to prefer cultivars that have long, slender, pointed, or urn-shaped buds opening to perfectly imbricated flowers of not less than semidouble petallage and preferably double or very double in this respect. (I have often wondered if the form of the “first Hybrid Tea”, La France, could have set the style for the roses of today).  The bud form which is popular today is not very difficult to achieve, as many of the present prospective parent cultivars have this characteristic. However, the form of the open bloom tends to the informal and irregular, and unfortunately often a confused or lopsided effect is created. If one does not have both parents with fine form in the open flower, then it is prudent to have at least one of them with such form or the breeder will preclude the possibility of having a meaningful quantity of progeny plants with acceptable open ‘flower form.

Size and Shape of Foliage. As near as I can determine, most rosarians prefer foliage that is more or less flat in character, large, heavy, leathery, and perhaps glossy. All of these qualities except the last seem to be difficult to attain and, in combination, this is particularly so. Experience has shown that it is very difficult to obtain foliage of medium to large size from a cross where even one parent is afflicted with small foliage.

Some growers contend that this is not such a handicap in the Floribunda class, but most would concede that it is a handicap in a popularity contest among Hybrid Teas.

Finally, I should point out that I do not intend to imply that these observations, either singly or in combination, may be considered total objectives in breeding roses. Obviously, the form, colour, substance and so on of the flower itself must be the final measuring stick of a rose-cultivar’s value. The foregoing qualities are merely shown as the principal road blocks to reaching our final destination.

A most important experience, from my point of view, is fairly frequent contact with buyers of rose plants, particularly those sufficiently interested to show them at flower shows or to judge them. Such experience is for me a “must”, not only for inspiration but for education. To know what my fellow rose lovers see as beautiful in the rose sets a pattern for my own effort, and it is always satisfying to see some of the cultivars from one’s own effort appearing in a rose show accompanied by a blue ribbon.

COLUMBUS QUEEN. H.T: (La Jolla x Unnamed Seedling).

The light pink blooms with darker outside tones are produced on long stems by a strong growing. disease resistant bush. One of the best garden cultivars to be released over recent  years. Geneva Gold Medal


Raised by Armstrong and Swim.

-Photo by courtesy Armstrong Nurseries


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