Dahlia Roots, Bulbs, or Tubers: What Should We Call Them?

Originally published as The Evolution of the Dahlia: Chapter Fourteen (1931)

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 Roots, Bulbs, or Tubers, Which?, Broomall turns from propagation practice to the terminology of the dahlia’s underground structures.

He objects first to the common practice of calling dahlias “bulbs.” His objection is practical as well as botanical. Inexperienced growers, he argues, may assume that dahlia “bulbs” should be planted in autumn along with tulips, hyacinths, and narcissus, potentially destroying the stock in colder regions. He also rejects the term because the dahlia’s underground structures are not layered like an onion.

Broomall then acknowledges a different problem. Botanists and plantsmen, he says, may object that the structures usually called dahlia tubers are technically roots. He does not claim decisive scientific authority against them. Instead, he argues for practical clarity. If both the enlarged overwintering structures and the fibrous feeding system are called “roots,” growers cannot easily tell which structure is meant.

He therefore reserves “tuber” for the enlarged structures that carry the plant from one season to the next and “root” for the fibrous structures that absorb water and nourishment. His distinction is functional and practical rather than a complete botanical anatomy.

Chapter Fourteen is the final known numbered installment, but nothing within it identifies it as the intended conclusion of Broomall’s projected book. Its placement after Chapter Thirteen is editorial rather than authorially specified: Thirteen considers propagation, buried joints, planting depth, and tuber formation; Fourteen clarifies the terminology of the structures involved.

The chapter appeared in the 1931 Success Dahlia Gardens Catalog. The illustrations are from a 1923 USDA booklet on growing dahlias, not from Broomall’s publication.

I am going to call attention to a subject which appears to me to be of importance to Dahlia growers; I believe things should be called by their right names and everything possible should be done to avoid misunderstanding in the minds of amateurs and the public in general.

I refer to the practice of many amateurs and a number of professional growers as well, in referring to the part of the Dahlia which we plant as “Bulbs.” I object to this practice for two reasons—First, it leads to confusion in the minds of some amateurs who, thinking they are “Bulbs,” get the idea in their heads that they should be planted in the fall at the time hardy bulbs are planted, hence the spectacle of a customer coming to a Dahlia Farm in November to get his Dahlia “Bulbs.”

Now that is the proper time or even later to plant Tulips, Hyacinths, Narcissus, etc., but to plant Dahlias at that time would, in many parts of the country, mean the loss of the tubers.

The second reason I object to calling them “Bulbs” is that they are not bulbs; “there ain’t no sich animal” as a Dahlia Bulb; the Dictionary says a Bulb is constructed in layers, like an onion, for instance, and the Dahlia never does it that way.

Nor can I approve of the habit of some old fashioned people who allude to Dahlia Tubers as Potatoes or Toes, for they certainly lack the multiplicity of eyes of the one or nails of the other.

I know that very learned Plantsmen and Botanists claim that the Dahlia roots are not Tubers; to be strictly correct they are just “Roots” or underground branches of the plant, while a real tuber such as the potato, for instance, is not borne directly on the base of the plant.

Now, technically speaking, these learned gentlemen may be right when they say Dahlia Tubers are just “Roots,” but unless we have some way of making a distinction between that part of the roots that have been created for preserving the germ of life from one season to the next, and the fibrous roots which feed the plant, how is anyone going to know which we refer to if we call both of them “Roots”?

Webster defines Tuber as “a fleshy rounded stem or root usually containing starchy matter.” It seems to me that this is a very good description of a Dahlia Tuber, and I shall continue to call them tubers so that readers will know that I am not referring to the feeding fibrous roots, and when I say roots I do not refer to the tubers.

I shall continue to use the term Tuber not for the sake of being contrary, but in order to avoid possible confusion and misunderstanding.

It seems to me it would often be awkward and inconvenient to have to explain when Roots were mentioned whether I meant the Tubers or the Fibrous Roots.

So I trust my hair-splitting friend will pardon me if for the sake of clarity of meaning I continue to say Tubers, which, according to Webster, they appear to be.

Roots feed the plant, draw the nourishment from Mother Earth; Tubers do not do this only to a very limited extent and for a limited period. They were created as storehouses of sap to preserve the germ of life from one season to the next.

Tubers do not function as roots at all, and could not thrive if there were no Roots to feed and sustain them as well as the whole plant above.

Editor's note. The following passage is excerpted from “Good Cultivation,” an installment of Broomall's 1933–1934 newspaper series My Experiences in the Improvement of Plants. Written several years after the numbered chapters, it is placed here editorially because its practical discussion of tubers, crowns, sprouts, and feeding roots applies the distinctions developed in Chapters Thirteen and Fourteen. It is not part of Chapter Fourteen, a missing numbered chapter or Chapter Fifteen, and is not evidence that Broomall intended this sequence. The complete installment appears with My Experiences in the Improvement of Plants later in this volume. 

In Southern California dry roots planted in March will begin blooming in May or June, and be at their best in midsummer. Green plants grown from cuttings (or seedlings) planted as late as July first will, if properly treated, give excellent results in the fall.

If planted in a single row, plant them at least three feet apart. They may be planted a little closer for hedge effect, but not if large flowers are desired. For when they are planted too close, they will rob each other and it will be a question of the survival of the strongest, and not always of the fittest, or most desirable.

If more than one row is wanted, the rows should be at least four feet apart. Make the holes not less than five inches deep, so that the upper side of the tuber will be four inches below the surface. Lay the tubers in a horizontal position with the eyes, or sprouts if any are showing, uppermost. Never stand them on end. I know not why, but many inexperienced amateurs I have met have the idea that a Dahlia tuber should stand up. And if let alone, they will probably stand half of them wrong end up. The first thing a dahlia tuber does after being planted is to throw out feeding rootlets at the end of the tuber farthest from the crown, and a depth of four inches is most favorable for such root action, and four inches is likewise the proper depth for the crown of the tuber from which the tender sprout must push its way to the light and air at the surface. Hence the planting of the tuber in a horizontal position is best for quick action for both roots and sprouts of the plant to be.

1. Practical and botanical terminology. Broomall acknowledges that botanists and plantsmen may regard the dahlia’s enlarged underground structures as roots rather than tubers. His defense of “tuber” is primarily practical: he wants one term for the enlarged structures that carry the plant from season to season and another for the fibrous roots that absorb water and nourishment. His terminology is preserved as his practical system rather than presented as a complete modern botanical classification.

2. Webster’s definition of “tuber.” Broomall quotes Webster as defining a tuber as “a fleshy rounded stem or root usually containing starchy matter.” The wording is preserved as printed, but the particular Webster dictionary edition and entry he used have not been independently identified.

3. Feeding roots and storage structures. Broomall describes fibrous roots as the structures that feed the plant and tubers as seasonal “storehouses of sap,” going so far as to say that tubers “do not function as roots at all.” This is preserved as his historical functional model. It does not map precisely onto his terminology in earlier chapters or onto modern botanical anatomy.

4. Final known numbered chapter. Chapter Fourteen is the last numbered installment presently known in the surviving series. It contains no statement that it was intended as the conclusion, no retrospective summary of the numbered chapters, and no announcement that Broomall’s projected book had been completed.

5. The later planting excerpt. “Planting the Dahlia” is excerpted from Broomall’s 1933–1934 newspaper series My Experiences in the Improvement of Plants and was written after the numbered Evolution of the Dahlia chapters. It is placed here editorially because its discussion of tubers, crowns, sprouts, planting depth, and feeding roots applies the distinctions developed in Chapters Thirteen and Fourteen. The complete installment is preserved separately with My Experiences in the Improvement of Plants.