Variation in Dahlias: Plant Food, Cultivation, and Doubleness

Originally published as The Evolution of the Dahlia: Chapter Four (1921)

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 Variation, Broomall returns to one of the principles announced in Chapter One and gives it a more systematic explanation. Plants vary naturally, he argues, but cultivation magnifies those differences because it alters environment and available nourishment. The dahlia, which he characterizes as a particularly heavy feeder, therefore becomes for him an unusually responsive subject for deliberate improvement.

This chapter is particularly important because it records a genuine change in Broomall’s thinking. In 1918 he had proposed repeated pollination as the primary cause of the first double dahlia. By 1921 he instead attributed the original doubleness principally to a superabundance of plant food. At the same time, he retains his earlier conviction that an established double dahlia does not permanently revert: imperfect flowers are temporary expressions of unfavorable conditions, not evidence that the inherited character has disappeared.

Its placement immediately after Chapter Two is editorial. Broomall did not mark Chapter Four as the next step after Two; placing it here keeps his revision of the opening explanation legible while that earlier argument is still fresh. Chapter Four itself provides firmer guidance forward: a separate pre-announcement following the chapter states that Chapter Five would take up another factor in dahlia variation.

The text printed here is from J. J. Broomall’s 1921 Dahlia Guide.

The variation of plants is as unlimited, and as impossible of complete understanding, as is the immeasurability of time and space; but there are certain phases of plant variation which we can understand, and the better we understand them the more successful will we be in our effort to improve plants.

Nature never makes any two plants alike; not even two peas in a pod are exactly alike. The variation of many plants in their wild state is so slight as to be scarcely noticeable; but when plants are brought under cultivation, the variation is greatly increased. As this change is generally accompanied by a great change in the amount and character of plant food, it is not surprising that such plants should change greatly in character.

The Dahlia is a gross feeder, a plant capable of making use of plant food very rapidly; hence it was inevitable when its environment was such that it could get all the nourishment it could make use of that it should do something different.

The principal cause of the first Double Dahlia was a superabundance of plant food; and it naturally follows that the same favorable conditions that caused the Dahlia to become larger and more double in the first place must be maintained, or the plants cannot successfully and completely perform the greater task which man in co-operation with the forces of nature has imposed upon them.

While there may be many causes for the failure of Dahlias to make perfect flowers, the most frequent cause is lack of proper nourishment. Many growers have the idea when a Dahlia fails to make perfect flowers that it is “going back”—reverting to the original type; this is a mistake.

I have Dahlias that I have been growing for over 20 years that sometimes fail when climatic or soil conditions are unfavorable; but they have never failed to again make perfect flowers when everything was favorable. Dahlias do not go back; the failures when they occur are only temporary, never permanent. A Dahlia once double is always double. I have seen such absolute proof of this that there is no room for argument; it is an established fact.

A New Jersey correspondent writes that his George Walters and Dr. Texis have “run out”—failed to make good flowers; and he thinks it is because he has grown them two years in succession on the same ground, so he desires to get a fresh stock of those varieties to plant next season.

Now Mr. A., I did not sell you those roots; nevertheless, I believe they are all right. The trouble lies not with the Dahlias but with the soil. Either conditions were unfavorable, or your soil is weak in some element of plant food. Find out what is the matter with your soil, by experimenting with different fertilizers or by chemical analysis if necessary, and when your soil is improved take my word for it, George and the Dr. will run in again.

Last year my crop of Golden West was a partial failure. The place where I cut my best blooms, and the only blooms fit for exhibition, was where the same stock had been grown for five years in succession. Now this happens to be my best soil, and the reason it is the best is because it contains more humus than any other part of the farm.

The addition of humus to soils not only is valuable for the plant food contained in the humus; it also makes the plant food that is already in the soil more readily obtainable by the plants. 

I would urge you to read what I say on a preceding page in regard to conservation of the soil and then “go thou and do likewise”; and you can’t do too much of it.

I hear a great deal about “Bud Variation,” that some strain of a variety produce much better flowers than others. For instance I am told a certain grower has a superior strain of “Golden West.” Granted that this is so, what caused it? There can be but one answer, and that is the plant food in the soil that nourished those plants; and any other roots of the Golden West would produce equally as good flowers in the same soil and under the same conditions.

Few Dahlias are more consistently double than “Helen Durnbaugh,” yet I have had plants of this variety that produced perfectly single flowers on some branches. Did this show it had “gone back?” Not a bit of it.

In a time of extreme heat the plant had suffered from lack of moisture, with the result that some of the branches became shrunken and hardened so that the flow of sap was cut down to the minimum, making it impossible for those branches to produce perfect flowers. While the restricted flow of sap interferes with the circulation of the life-blood of the plant, it does not necessarily follow that the tubers are injured; and the same tubers will produce good results the following year if conditions are favorable.

There are some causes of failure for which the soil is not to blame.

First. Never plant old tubers if it can be avoided; in case such must be used it is much better to raise green plants from them than to plant the tubers; for old tubers are apt to be more or less diseased. The fibres in such have become hardened, so that the flow of sap is interfered with; while green plants will soon form root systems and tubers of their own that will be free from disease.

Another cause of imperfect flowers is Excessive Propagation, where roots are forced under too much heat, and the plants taken from them are also forced under abnormal conditions, and especially where the roots have been used too long under such conditions; the plants will be so strained and their vitality so weakened that they cannot possibly give satisfactory results.

The tubers produced by such plants will, however, be all right for planting the following year, provided they have had good culture in the field; for here again the deterioration is temporary, not permanent. The failure, no matter what the cause, is never permanent.

1. Broomall’s changing explanation of doubleness. Broomall’s explanation of the first double dahlia changed between Chapters One and Four. In 1918 he gave repeated pollenization, usually through increased insect visitation, the primary role, with cultivation and inheritance as additional causes. Here, in 1921, he instead attributes the first doubleness principally to a superabundance of plant food. His separate claim that an established double dahlia may temporarily produce imperfect flowers without permanently reverting remains consistent across both chapters.

2. Golden West and bud variation. Broomall rejects the idea that a superior strain of Golden West could arise through an intrinsic bud difference and attributes the reported superiority entirely to soil nutrition. His later position was less categorical. In a 1934 installment of My Experiences in the Improvement of Plants, he accepted bud sports as genuine branch-level variations, discussed preserving them through cuttings, and acknowledged that they might later revert. Chapter Seven and earlier catalog notes also record lasting changes from variegated to solid-colored flowers.

3. Historical plant physiology and disease. This chapter combines practical observation with biological assumptions characteristic of Broomall’s period. Among them are his claims that imperfect doubleness is always temporary, that superior performance in Golden West can be explained entirely by soil nutrition, that green plants raised from old diseased tubers will form root systems and tubers free from disease, and that deterioration caused by forcing or unfavorable conditions is never permanent. These statements are preserved as part of Broomall’s historical reasoning rather than as modern conclusions in genetics, plant pathology, virology, or floral-development science.

4. Dr. Texis. The 1921 source prints “Dr. Texis.” The cultivar is documented elsewhere in Broomall’s catalog as Dr. Tevis. The printed form has been retained here as a source reading rather than silently corrected.