Color and Fragrance in Dahlias: Light, Perception, and Scent

Originally published as The Evolution of the Dahlia: Chapter Ten (1927)

Original text by J. J. Broomall is in the public domain.

Compilation, editorial notes, introduction, biography, and revised text copyright © 2026 by Steve K. Lloyd. All rights reserved.

In Color and Fragrance of Dahlias, Broomall returns to color three years after Chapter Seven, but approaches the subject from a different direction. Rather than beginning with dramatic changes in individual cultivars, he starts with the practical difficulty of describing color at all. Blended hues, changing tints across a petal, viewing distance, and artificial light all complicate the attempt to assign a single stable name to a flower’s appearance.

From perception he moves back toward environment. Temperature and soil composition again become possible causes of color variation, and Broomall repeats his speculation that a better understanding of soil chemistry might eventually contribute to producing colors not yet attained, including blue.

The second half opens a substantially new inquiry: fragrance. Broomall insists that some dahlias are fragrant, recalls a sweet-scented form for which he says he received a certificate in 1908, and considers why scent may vary with flower development, time of day, heat, and repeated smelling. Color and fragrance are ultimately joined by the same methodological question: when the sensory effect changes, is the cause in the plant, its environment, or the observer?

The present placement beside Chapter Seven reflects this strong conceptual relationship. It should not be read as evidence that Broomall himself specified their adjacency.

The text printed here is from J. J. Broomall’s 1927 Dahlia Guide.

In the ever-increasing variation in the color of Dahlias the task of correctly describing the different tints is becoming more and more difficult.

The use of Ridgeway’s color chart, which appears to be generally accepted as the standard authority on color, is a great help in describing the various tints, and the reader of a catalog may be given a fairly good idea as to what the flower will look like.

One great difficulty lies in determining, where two or more colors or tints are blended in a flower, which is the predominating color. Frequently one petal will show three or four distinct colors from base to tip, to say nothing of various tints where the different colors merge.

Perhaps the easiest way is to describe the general color effect of the whole flower, and here again is a difficulty, for in shaded flowers the color will appear quite different fifty or a hundred feet distant from what it does at close range upon closer inspection.

In most Dahlia shows it is necessary to use artificial light and the difference of appearance in sunlight or under artificial light in some flowers is so great that it is often a difficult matter to recognize the variety.

Take the Siskiyou, for instance. I do not admire its color in the sunlight, but under artificial light it appears beautiful to me.

Light yellows seldom show well under artificial light, but yellows that are shaded with orange show extra fine.

It seems to me that the color of many Dahlias should not be judged under lamplight, for only in the natural light can a correct estimate of the color be arrived at.

There are several causes that will affect the color of Dahlias growing in the field. Perhaps the most common cause is changes of temperature.

I have seen many Dahlias vary so greatly in color from changes of temperature as to be almost unrecognizable. Especially does this appear to be true of pink and salmon shades having a yellow base.

Late in the Fall when the nights become quite cool many of such varieties will have lost their color so that they will be only an indifferent yellow or straw color and will have entirely lost their attractiveness.

Another frequent cause of Dahlias failing to come true to their original color is change of soil. Many varieties will be much lighter or darker in some soils than they will in another locality, and this is undoubtedly due to the difference in the chemical composition of the soils.

If we could determine by chemical analysis what property it is in the soil that will improve or increase a desired color, we will have made a great advance in the improvement of the Dahlia, and we might hope in the course of time to obtain a Blue Dahlia.

While such a color in the Dahlia may at this time seem improbable, I do not regard it as impossible, for we are living in an age when much that has been regarded as impossible has become established fact.

I often hear people complain that the Dahlia has no fragrance; this is a mistake. The Dahlia IS FRAGRANT, at least a few of them are.

In 1908 I was awarded a Certificate of merit for a Sweet-Scented Dahlia by the Pasadena Gardeners Association (now the Pasadena Horticultural Society).

I lost that variety but have had several since, most of which I have lost chiefly because of carelessness or neglect due to an oversupply of work.

All the Fragrant Dahlias that I have seen or smelled have been single or nearly single flowers.

I regard a Fragrant Double Dahlia as being extremely improbable, if not impossible, for the fragrance comes from the generative organs which in a double Dahlia are either absent, imperfectly developed, or so completely submerged by the multiplicity of petals that it is very doubtful even if present if they would develop sufficiently to exude any fragrance.

The Fragrant Dahlias I have seen have all, without exception, had two faults or characteristics. One is their inconstancy.

I have had Dahlias almost as fragrant as a Honeysuckle or Violet, so fragrant at times that I could smell the pleasing odor as I walked by them, and at other times I could not detect the slightest odor when my nose was near enough the flower to touch it.

I have noticed that they were generally more fragrant in the morning, and seldom in the heat of the day; also that the fragrance was greater in the flowers in which the organs were most fully developed.

Another fault of the Fragrant Dahlia is the elusiveness of the odor. The first smell of a Fragrant Dahlia is almost invariably the sweetest.

It may be that repeated smelling exhausts the fragrance of the flower, but I am more inclined to think that there is something in the odor that has a tendency to temporarily dull the sense of smell.

In smelling Dahlias I have found that for one variety that gives out a pleasing odor there are many that are far from being pleasant to smell. In fact, I have found some where the odor was so strong and disagreeable as to be absolutely painful to the nostrils.

Now the question arises, what can be the cause of this great difference of odor?

I believe that there is always a cause for every effect, but it is sometimes extremely difficult to find out the cause.

As in the color of Dahlias I am confident that the chemical composition of the soil has much to do with the odor in the Greatest of all Garden Flowers.

It is my intention to continue trying to get a real satisfactory Fragrant Dahlia by two methods, by selection and by experimenting in different soils and the use of various kinds of plant food.

It may be that I shall not live to accomplish my undertaking, but I can at least try, and if what I have written should induce others to do likewise I will not have written in vain.

Yours for better Dahlias,

J. J. BROOMALL.

1. “Ridgeway’s color chart.” The source prints “Ridgeway’s” both here and in the 1927 catalog introduction that directs readers to this chapter. The apparent reference is to the color nomenclature associated with Robert Ridgway, but Broomall’s printed spelling has been preserved.

2. The 1908 Certificate of Merit. Broomall states that he received a Certificate of Merit from the Pasadena Gardeners Association in 1908 for a sweet-scented dahlia, and identifies that organization parenthetically as the present Pasadena Horticultural Society. The statement is preserved as printed, but neither the award nor the institutional identification has been independently confirmed.

3. Fragrance and the “generative organs.” Broomall attributes dahlia fragrance to the reproductive structures and therefore regards a fully double fragrant dahlia as extremely improbable or impossible. This explanation is preserved as part of his historical botanical reasoning rather than as a modern conclusion about the biology of floral scent.

4. Soil chemistry, color, and fragrance. Broomall again proposes that soil chemistry may influence flower color and extends the same reasoning to fragrance. These are preserved as his historical hypotheses rather than as modern biochemical or genetic explanations.