Dahlia Seeds and Seedlings: Breeding, Heredity, and Why Tubers Get Blamed

Originally published as The Evolution of the Dahlia: Chapter Nine (1926)

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.

After the preceding chapters’ widening attention to color, climate, and cultivar behavior, Seeds and Seedlings, and Some Other Topics turns the reader back toward breeding and heredity. Broomall also pauses long enough here to describe what he intended The Evolution of the Dahlia eventually to become. Responding to readers who could no longer obtain all of the earlier installments, he says that he plans to “re-write and re-arrange” the chapters, add further material on culture and propagation, and publish the whole as a book. This is the clearest surviving statement that Broomall himself regarded the numbered series as material for a larger work still subject to revision.

The chapter then turns to breeding. Broomall warns that even deliberate hand pollination cannot guarantee known parentage unless unwanted pollen is excluded, and he emphasizes the unpredictable influence of remote ancestry. Exceptional seedlings, he says, are exceedingly rare, and the visible excellence of a parent does not by itself establish its breeding value.

He also says that he believes there is a way to obtain desired crosses and that in “a future chapter” he may explain it. No identification of a surviving later chapter as the fulfillment of that promise is made here.

The final movement returns to a familiar problem: whether imperfect flowers prove that a cultivar has permanently deteriorated. Using Ambassador, Broomall compares crowding with open space, heat with cooler weather, and even different stems on the same plant. His argument is again diagnostic rather than merely cultural: appearances should not be accepted as evidence of permanent inherited failure until competing causes have been investigated.

Its placement before Chapter Twelve is editorial rather than authorially specified. Chapter Nine establishes the limits of prediction in breeding; Chapter Twelve develops the empirical testing and severe selection by which Broomall attempted to work within those limits.

The text printed here is from J. J. Broomall’s 1926 Dahlia Guide.

I have received requests for the earlier chapters of “Evolution of the Dahlia,” some of my friends desiring to obtain all of the previous chapters.

I regret to say that it is impossible for me to supply them, as my stock of some of the issues of the “Dahlia Guide” is entirely exhausted.

I have no copy of my 1903 Catalogue and would be glad to exchange a $10.00 tuber for one.

In regard to my articles on the Dahlia I will say that it is my intention to re-write and re-arrange the chapters I have written, also to write several additional chapters covering all the principles of Dahlia culture and propagation, and to publish the same in book form.

This book will be sold for not less than $1.00 nor more than $2.00, and I expect to lose money on it at that, as it costs considerable to publish a book, and at best the demand is likely to be quite limited.

I am not writing this with the expectation of making anything on the venture but wholly with the idea of giving others the benefit of my years of experience with Dahlias.

As to how soon the publication of this work is undertaken depends largely upon you who read this. If you think you would be interested in reading it, drop me a post-card to that effect so that I may know that there are some who would be interested in it.

I will tell the best I can about my methods of raising seeds and seedlings and give such other information as may appear to me to be useful and interesting to growers of the Dahlia.

I have had a great many requests for Dahlia Seed. I will state that I have no Dahlia Seed for sale.

I cannot raise enough GOOD seed for my own use, and I will not sell any other kind.

I suppose the would be buyers have an idea that they would get something good from my seed; I will say in all candor that they are very liable to be disappointed.

They would probably get some very pretty flowers (I throw away thousands of them).

The real good Dahlia, the Dahlia that is distinct from and better than any of its predecessors, will seldom average more than one in a thousand, and the real top-notcher such as Eagle Rock Beauty for instance, is one in Ten Thousands.

It is true that growers sometimes obtain a fine Dahlia from a limited number of seedlings, but such may be regarded as accidents, and are far from being the rule.

I see that some Growers offer for sale hand-pollenized seed; this I regard as BUNK.

Such Growers are either wilfully misleading the public or else they know very little about Dahlias; unless the flower from which seed has been obtained has been protected from ALL insect visitation, it is incorrect to call it hand-pollenized, for the work of bees and other insects will be many times more effective than all the work that may have been bestowed upon them by the grower with his brush.

When all insects have been excluded from a blossom you will obtain very few seeds, and they will usually produce weak plants and undesirable flowers.

I am speaking now from experience.

Purely hand-pollenized seed could not be sold for any reasonable price, and in the great majority of cases would be disappointing.

I believe that there is a way to obtain the crosses desired, and in a future chapter I may endeavor to explain how it might be done.

Even then we are gambling with Nature, for with the parent flowers which we now use, which are the results of years of crossing and re-crossing, the heredity of the Dahlia steps in and is likely to upset our calculations, for the seedlings are just as liable to partake of the characteristics of some of their many more remote ancestors as they are to resemble their direct parents; hence the importance of selecting parents in which the best traits of inheritability are shown.

I have found that some of the best Dahlias we now have are deficient in this respect.

At the risk of being monotonous I am going to say more in regard to the failure of Double Dahlias to come perfect.

I suppose I have received a greater amount of praise for Ambassador than for any Dahlia I have introduced and also a greater number of complaints of its failure to come double.

In the first place there is a vast difference in the constitution and action of Dahlias under unfavorable conditions.

An extreme of temperature, for instance, may have but little effect upon one variety, but be little short of disastrous to another.

I have carefully watched the actions of Ambassador under various conditions.

I have some rows of it that have grown in the same place undisturbed for four years. When they bloomed last summer probably not more than 10% came double, which I think was due to the overcrowded condition of the much too numerous stalks; they were robbing each other in their struggle for existence.

Where there was a break in the row and a plant had plenty of room it produced nearly 100% perfect flowers.

A row in my main garden which was newly planted began blooming in hot weather and produced only about 5% perfect flowers, but later on, when we had quite a long spell of cooler weather, nearly 75% of the flowers were double; this would seem to indicate that the Ambassador does not like extreme hot weather.

Extreme heat causes the hardening of fibres in the stalks or stems so that the flow of sap is restricted; the blooms cannot fully develop unless the sap (the life-blood of the plant) can flow freely and uninterruptedly.

Some stems may be affected and others not; for I have seen perfect flowers and others almost single on the same plant, which shows that the cause of failure is in the branches or stems, and not in the roots, for if it was the fault of the tubers or the root system ALL of the flowers would be poor.

While this is only one of many causes of poor flowers, I am convinced that in the majority of cases the trouble is above ground, and not in the tubers.

The Head of one of the largest retail firms in America told me that they were going to discard their stock of Ambassador and procure fresh stock from a nearby Grower whose Ambassadors grow to perfection.

Now unless the tubers are diseased or infested by insects (of which I have no knowledge) I would not discard them, for I do not believe the fault lies with the tubers.

In 27 years I have never discarded Dahlias on account of their failure to make perfect flowers.

I have planted such Dahlias year after year, and seldom have I been disappointed.

I will repeat a previous statement, “When a Dahlia starts to grow it quickly forms a new set of tubers and by the time it has reached the blooming stage it is obtaining by far the greater part of its nourishment through the newly formed root system, and it matters little what the old tuber may have done the previous year. So why blame all the shortcomings on the tubers?”

Yours for a better understanding of the Dahlia.

J. J. BROOMALL.

1. Broomall’s proposed book. Broomall’s statement that he intended to “re-write and re-arrange” the existing chapters, add further chapters on culture and propagation, and publish the whole in book form is the strongest surviving documentary evidence that The Evolution of the Dahlia was conceived as material for a larger unfinished work. It does not preserve the final order he would have chosen.

2. Hand-pollenized seed. Broomall’s objection is specifically to claims of controlled parentage when insect visitation had not been excluded. He does not reject deliberate crossing itself; immediately afterward he says that he believes desired crosses can be obtained.

3. Seedling rarity. Broomall estimates that a genuinely superior dahlia may occur only once in a thousand seedlings and that an exceptional “top-notcher” may be “one in Ten Thousands.” These are preserved as his practical estimates. Other writings give different figures for other stages of selection and market survival, so the numbers should not be harmonized into a single statistical rate.

4. Ambassador and the percentage differences. In this chapter Broomall reports approximately 10 percent double flowers in overcrowded plants, nearly 100 percent where a plant had ample room, about 5 percent perfect flowers during hot weather, and nearly 75 percent later in cooler weather. Chapter Eleven gives different figures for Ambassador under extreme heat and cooler weather. Both sets of percentages are preserved as printed; the surviving texts do not establish whether they represent different observations or approximate recollection.

5. Heat, fibres, and sap flow. Broomall distinguishes his garden observations from his physiological explanation of them. His claim that extreme heat hardens stem fibres and restricts the flow of sap is preserved as part of his historical reasoning rather than as modern plant physiology.

6. “In 27 years.” Broomall’s statement that he had never discarded dahlias for imperfect flowers “in 27 years” is preserved as printed. Chapter Eight had used “26 years” one year earlier, and later recollections may point to a slightly different starting date. The discrepancy remains unresolved and has not been silently reconciled.