Growing Dahlias from Cuttings: Propagation, Planting Depth, and Plant Vigor

Originally published as The Evolution of the Dahlia: Chapter Thirteen (1930)

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.

The Green Plant Question is Broomall’s fullest surviving numbered treatment of dahlia propagation from cuttings.

Drawing on more than thirty years of experience with what he calls “green plants,” Broomall argues that plants propagated from cuttings can be fully satisfactory and, in some varieties, superior to tuber-grown stock. His central problem is therefore not whether green plants are inherently good or bad, but why some succeed and others fail.

He identifies excessive artificial heat and unnatural forcing as the most common cause of failure, contrasting those practices with his own deliberately slow system of cool propagation, limited heat, abundant air circulation, careful rooting and hardening, and late field planting. Yet he refuses to make even his preferred explanation universal. Excessive propagation is only one cause of stunting; insect injury and causes “as yet unfathomed” may also be involved.

The final movement connects propagation to plant structure through heel cuttings, buried joints, planting depth, and tuber formation. It then ends with an unusually important documentary announcement. Broomall says that he knows an outdoor method of increasing stock under natural conditions without injuring vitality, but deliberately withholds the procedure for inclusion in his intended book on The Evolution of the Dahlia, which he hoped to publish within a year.

No surviving source reviewed for this edition identifies itself as that promised method. Its absence is therefore preserved rather than repaired from later propagation material.

The chapter appeared in the 1930 Success Dahlia Gardens Catalog.

In discussing “The Green Plant Question” I shall endeavor to give my reasons for being very much in favor of green plants, that is, growing Dahlias from cuttings, and I will also try to explain why green plants of Dahlias are sometimes disappointing and a failure.

It is more than thirty years since I raised my first Dahlia plants from cuttings. For many years while I was in the Mail Order business I sold so close on many of the better varieties of Dahlias that I did not have near enough roots to plant, so that I was practically forced to propagate from cuttings in order to raise sufficient stock to meet the demand, with the result that quite often more than half my ground was filled with green plants.

The stock grown from such plants was almost without exception fully as satisfactory as stock grown from tubers. Some of the finest blooms I have ever obtained were produced by green plants, and in some varieties the blossoms were much more perfect and showed less tendency to produce flowers with open centers than the same kind grown from tubers.

On the other hand, I have tried to raise Dahlias from green plants supplied by other growers that sometimes were far from satisfactory and in some cases a total failure. Now I proceed upon the theory that there is always a CAUSE for every effect, whether the effect be good or bad, and I believe the most common cause for the failure of green plants is over-propagation by the use of too much artificial heat; the vitality of plants forced under excessive heat and unnatural environment is injured to such an extent that when grown they have not the strength necessary to produce perfect flowers, and, indeed, some are not strong enough to survive long after being planted out or, if they do manage to live, prove to be only “stunts” that only get a few inches high all summer, not having the strength to make a normal growth much less a blossom or even a bud.

It is no wonder that people receiving such plants are disappointed and disgusted with green plants, and not understanding the cause, we can hardly blame them for their poor opinion of green plants of Dahlias.

Right here I want to warn some of the Eastern Growers, and a few Californians as well, that if they persist in this ruinous practice of excessive forcing they will not only be doing great harm to the Dahlia trade in general, but will injure themselves most of all, for disappointed customers caused by such tactics will surely prove a boomerang to their business.

When I receive a letter from a New Jersey customer in February telling me of the large number of cuttings he has started I KNOW that he must have used a great deal of heat; much more than is good for the vitality of the plants, and if persisted in the majority of those plants will not pay for the trouble of planting them.

Now at the time that letter was received my clumps in the propagating bench had not even started to sprout although I am living in a much warmer climate than New Jersey. I am well aware of the fact that some of my fellow growers think I am slow and old-fashioned in my propagating, but I had rather be two or three months behind the other fellow with my green plants than to have a lot of irate customers looking for me at the Fall Flower Show.

Here is how I start my green plants: I bed my clumps in the propagation bench using a mixture of sandy loam and ground peat, the first week in January, using sufficient dirt to cover the tubers, but leaving the crown even with the surface with little or no earth over it (the crown).

I never use any heat under the bench containing the clumps, and very little under the cutting bench. In fact, I make no effort to keep the temperature above 50 at night or in cloudy weather and do not worry if it falls to 40 on a frosty night, although I do not advise such a low temperature as 40, but at all times I try to have air circulating, in fact try to keep conditions as near natural as possible without getting too near the freezing point.

Naturally, under these conditions, the Dahlias are slow in starting so that I seldom get many cuttings before the latter part of March and do my heaviest propagating in April and May, the most of my plants not being ready for planting in the field (after being potted and hardened off in the lath house) until June and the later ones in July.

After they get well started they grow rapidly and by Fall are blooming profusely and the most of them produce a fair crop of healthy tubers.

It is generally the practice to root the cuttings in pure sand, and they should be potted in 2 1-2-inch pots as soon as rooted. If they only have one rootlet not more than one-eighth inch long, it is safe to pot them, and is much better than leaving them in the sand too long as the sand contains very little plant food and cuttings left in it too long will develop a lot of stringy roots that are half-starved for nourishment and not good for the vigor of the plants.

I believe a mixture of leaf-mold with the sand is better for Dahlia cuttings as the leaf-mold contains plenty of plant food so that the growth will not be weakened by remaining longer in the bench. There may be more danger of damping off if leaf-mold is used, as it is apt to contain some fungus unless it has been baked, but if plenty of air is in circulation, there is not much danger of damping off as the most frequent cause of damping off fungus in the cutting bench is STAGNANT AIR AND TOO MUCH ARTIFICIAL HEAT.

The first Dahlia cuttings I ever grew were rooted about 1897 out of doors in virgin soil that contained a liberal mixture of leaf-mold derived principally from maple trees; those cuttings grew in a remarkably short time and bloomed to perfection. But that was in Snohomish County, Washington, where conditions happened to be “just right” and would seldom be practicable here or in many other localities.

It is, however, not strictly necessary to have a hot-house in which to grow Dahlia plants successfully. For many years I grew my green plants in hot-beds with satisfactory results except when, for instance, a toad seemed to think the sand a proper place in which to bury himself and upheaved quite a number of cuttings in so doing—but whatever you do, DON’T KILL THE TOADS: they are our friends.

There is one great advantage in using hot-beds: in warm sunshiny weather the tops can be removed entirely and the plants will be outdoors under natural conditions, and remember—the nearer we keep to natural conditions the more satisfactory the plants will be; such plants will be almost certain to give satisfaction.

I do not propose to take up the matter of stunts now, only to say that I do not want it understood that excessive propagation is the ONLY cause of stunts in Dahlias; it is ONLY ONE OF THE CAUSES; stunted growth or lack of growth may be due to the sting of some injurious insect or various other causes as yet unfathomed. The efforts of some writers to place all the blame for stunts on green plants is absurd.

The reason that green plants do not always produce tubers is that sometimes the cutting has been rooted between joints. Such plants may grow and bloom but unless they are planted deep enough so that a joint is three inches below the surface they may not throw out tubers.

Heel cuttings are far the best, as they root more easily and are sure to make tubers. Where other cuttings are used, they must be planted deep enough to insure the proper covering of a joint.

I generally set my plants in a small trench or cavity so that by the time they are half-grown and the soil is about level from being cultivated the plants will be six inches deep, for it is better to err on the side of deep planting than not to plant deep enough.

I wish to say to our friends who are in a big hurry to increase their stock of a new variety that there is a way it can be done successfully out of doors under natural conditions without injuring the vitality of the Dahlia. Stock grown by the method I shall describe will not be suitable for filling orders but will be good for home planting, producing roots that will be good for commercial use the following season.

To the curious I will say that it will be useless to write for an explanation of this method; it will be described fully in my book on the “Evolution of the Dahlia,” which I hope to be able to publish within a year, in which I will endeavor to the best of my ability to give others the benefit of my experience of a third of a century of Dahlia Culture.

Yours for Better Dahlias,

November 2, 1929.

1. Excessive forcing and plant vitality. Broomall repeatedly associates excessive artificial heat and unnatural forcing with reduced plant vitality and later failure in the field. These explanations are preserved as part of his historical horticultural reasoning rather than translated into modern physiological terminology.

2. Propagation temperatures. Broomall gives nighttime or cloudy-weather temperatures of 50 and 40 without printed degree symbols. Context indicates Fahrenheit. He expressly says that he does not recommend 40 as an ideal temperature.

3. Rooting media and damping off. Broomall prefers leaf mold mixed with sand because he believes it supplies plant food to rooted cuttings, and he associates damping off with fungus, stagnant air, and excessive artificial heat. These explanations are preserved as his historical understanding of propagation and disease.

4. First cuttings “about 1897.” Broomall says that his first dahlia cuttings were rooted outdoors in Snohomish County, Washington, about 1897. That statement sits imperfectly beside earlier claims of twenty-six years of dahlia growing in 1925 and twenty-seven years in 1926. The differing autobiographical chronologies are preserved rather than forced into a single starting date.

5. Joints, planting depth, and tuber formation. Broomall states that cuttings rooted between joints may grow and bloom without forming tubers unless a joint is buried sufficiently deeply. He also prefers heel cuttings and says they are “sure to make tubers.” These claims are preserved as his historical anatomical and practical explanation of propagation.

6. The withheld outdoor method and intended book. Broomall says that he knows an outdoor method of rapidly increasing stock under natural conditions but deliberately withholds the procedure for inclusion in his intended book on The Evolution of the Dahlia, which he hoped to publish within a year. No surviving source examined for this reconstruction explicitly identifies itself as that promised method, and the passage does not establish that a finished manuscript or final table of contents ever existed.