Propagating Dahlias by Vegetative Grafting
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Time to read 13 min
This article is adapted from the book The Dahlia: History and Detailed Culture According to the Advice and Procedures of the Best Growers by Augustin-Claude-Simon Legrand. The author was a Member of The Royal Horticultural Society of Paris, and he lived 1765-1856.
The book was published in Paris in 1843 as Le Dahlia: Histoire Et Culture Détaillée, D'aphés Les Avis Et Procédés Des Meilleurs Cultivateurs.
Although the original French language work is in the public domain, this article has been translated and edited for the modern reader and contains new material.
This version is Copyright © 2024 by Steve K. Lloyd and may not be reproduced without permission.
Propagating Dahlias by Vegetative Grafting
Augustin Legrand’s Second Method of Multiplication (1843)
Translated & Edited by Steve Lloyd © 2024 All Rights Reserved
This method of propagation holds significant advantages in cultivation as it maintains and freely produces dahlias that could not otherwise reproduce through seeds.
The process of grafting generally involves joining a bud or young shoot onto root stock, so that the shoot integrates and gradually develops with the host. Grafting can only be successful when performed between growing parts of plants of the same species. The healing of grafts, meaning the union between the two attached parts, is facilitated by the plant's own sap, a very fluid material called cambium.
The success of dahlia grafting thus hinges on the immediate contact between the branch and the grafted tuber. This branch or shoot initially comes from the root of a rare and distinguished subject, typically induced to germinate artificially.
Although dahlias can be grafted throughout the favorable season, they are also grafted in winter, specifically in January and February. Since the grafts must be kept at a temperature of 50 to 59 degrees Fahrenheit (10 to 15 degrees Celsius), greenhouses are utilized. These accelerated grafts are mainly of interest to growers needing numerous shoots, which they can use to produce a large number of plants for sale in March and April.
In 1813, Baron de Tschoudy published a memo on general herbaceous grafting, highlighting the utility of this technique, which was already known in the 16th century. Indeed, J.-B. Porta, a learned Neapolitan naturalist, discussed this herbaceous graft in his work "Phytognomonica, libri XII", a sort of rural compendium, published in Frankfurt in 1592, in folio.
Mr. Blake, an English gardener, was the first to apply this grafting technique to a common dahlia tuber in 1821. It was crucial to propagate double dahlias, which were uncommon at the time. He cut his graft in a wedge shape on one side only, with a bud or eye at its lower end that rested on the edge of the tuber. The graft originated from the roots of this bud, and the stem grew from the eye reserved at the top.
In the harsh season, it becomes necessary to induce plant germination to create grafts. Branches can be quickly obtained by burying the tubers designated for propagation in a suitably heated layer of potting soil. These tubers, labeled with small numbered lead tags, are easily identifiable. Their offspring's progress is carefully monitored, and as soon as shoots with two pairs of leaves are obtained, the grafting operation commences.
Additionally, various tubers are set aside, preferably those with very thin necks (Plate IV, Figure 7); and some larger ones, in case the graft turns out to be somewhat large (Figure 8).
With everything thus prepared, operations proceed in various ways, but always conforming to these important principles:
1) The top part of the tuber is amputated to prevent possible growth from its own crown, which could thwart the grower's plans since the tuber serves merely as a means to quickly produce numerous subjects as desired (Plate IV, Figures 7 and 8).
2) A vertical slit is made on the tuber's skin (Plate V, Figure 12).
3) A young shoot that has been detached from the parent plant is inserted (Plate V, Figure 13).
For the amputation and the incision, naturally, a very sharp instrument is used. Various tools are employed: Plate IV, Figure 9, a standard grafting knife; Figure 10, a small blade more suitable for cutting cuttings or buds; Figure 11, a sharp blade, which is fitted with a handle at the end.
To use them, the cluster of tubers is placed on a table, and the tip of the tool is positioned in the angle formed by the tuber to be detached and the neck to which all tubercles are attached, so that the cutting edge faces the neck. The part of the tuber equipped with eyes that one wants to separate from the cluster is then detached.
This ensures that no tuber is left “blind”, a result not as easily achieved with a pruning knife. The inventor of this instrument is Mr. Chardon junior, gardener.
Make a wedge-shaped slit in the tuber as shown in Figure 12. Detail “c” shows the shape of the incision, and Detail “d” illustrates the shape of the piece that was removed.
The growing tip of the dahlia shoot to be grafted is shown in Figure 13, inserted snugly into the wedge-shaped slit carved into the tuber.
This slit being made on the tuber (Plate V, Figure 12c), in the desired manner, whether simple or more artistically combined, permits the insertion of a branch (Figure 13).
The joined parts may be secured with a tie, preferably a wool one, as it can expand with the growth of the branch. Many cultivators do not use this tie. None of the grafts by Messrs. Soutif, Roblin, or Chauvière require it. According to the latter's prudent observation, compressing the soil around the tuber suffices to maintain the two parts in perfect adhesion. A tie would seem necessary only in cases where the vertical slit is overly long and disproportionate to the graft, not compressing it entirely.
On the tuber (Plate V, Figure 14), the place where three amputations have been successively made is visible. Even after the amputated stem, there remains a shoot and two buds that will produce new shoots, and so on, virtually ad infinitum.
Once this operation is finished, the grafted tuber is buried in a layer of rich soil with the cut covered to a depth of about one inch. The graft carries a small lead label (Plate V, Figure 13 k) under the same number as the mother plant to prevent any confusion. In this example the number “127” has been used to identify this new grafted dahlia. These numbers are promptly noted for future reference.
This practice of numbering young subjects is not futile. The number—consistently attached to the name of the plant in all catalogs—allows one to know from the moment of registration what one possesses. The grower can deliver and receive the plant with full confidence.
This operation is not as cumbersome as one might think. It simply requires having at hand nine punches bearing the relief of numbers (the 6 serves for the 9), plus a small amount of very thin lead plates (Plate V, Figure 15 g) and a small hammer (Figure 15 h) all combined as shown in Figure 15. The box itself serves as an anvil, as it is a section of hollowed-out wood (Figure 15 j).
Editor’s note: The preceding paragraphs advise the reader that it is important to label one’s dahlias as they are propagated, and then instructs the grower on a seemingly simple manner of making labels using lead sheets, a series of numbered punches, and a small hammer. Reading these instructions 180 years after M. Legrand wrote these words, I am reminded of the myriad challenges–large and small–faced by dahlia propagators of the early years. Today we would simply grab our indelible garden marker and a plastic plant tag, make a label, and carry on.
Regarding young shoots, it is not always sufficient to amputate them and insert them immediately into the tuber; they require some more or less delicate preparations. This grafting operation can be performed in different ways, depending on the goal one aims to achieve, as we will detail below. To leave nothing to be desired regarding grafts, we shall delve into some specifics.
It is known that each leaf carries its bud [which today we would call leaf nodes; ~Ed.] The amputated branch will have four buds. The two base buds, being inserted into the tuber, will provide roots. The two upper buds will form its stem.
Note that if one leaves two inches or even less on the stem below the buds, this stem may indeed take root, but it may also not be very well preserved. Roots emerging from the middle of the branch will not produce buds. Sometimes in commerce, one sees grafts that have only one eye—they are still very easy to lose.
A surer way to free the plant is to employ this graft (Plate VI, Figure 16), which can only be used for a precious dahlia that one wishes to rejuvenate with all possible certainty. This graft is undoubtedly more secure than cutting.
An incision is made along the entire length of the tuber, as already indicated. A branch is shaped as shown in Figures 17 and 20. This branch should be long enough to extend beyond the tuber by 2 to 4 inches, onto which it is then fitted and tied.
Once this graft has healed and been nourished by the tuber (which roots very easily) new tubers form within the year.
The following year, the old tuber (Figure 18) which has served to nourish the graft, (Figure 18 n) can be removed without issue. However, it is not certain that these tubers will be capable of sprouting eyes the following year. Mr. Chauvière believes they do not carry the elements of buds.
It is always advisable to keep an eye (Figure 17 p) along the length of the incised branch, a practice widely adopted for all grafts. If the upper part of this branch were to rot, this eye could still suffice to preserve the plant. However, the tuber will need to be elevated to allow the eye to be exposed to light.
Figure 19 represents the grafted tuber viewed from the front; Figure 20, the incised branch viewed from the front; Figure 17, the same viewed in profile.
Here is a fact that will illustrate one of the first experiments related to dahlia grafting. Four years after Mr. Blake's experiment, in 1828, Mr. David, the king's gardener at the Orangerie of Saint-Cloud, operated as follows.
He split a shoot without a heel on a dahlia already reaching a height of a foot and a half. The shoot was 8 to 9 inches long, it bore four leaves, and the top was very little developed.
After squarely cutting the bottom of this shoot, he shaped it into a whistle in its non-colored part, to a length of about 2-½ inches. He purposely chose a tuber long exposed to the sun, with a thin, very elongated neck. Having horizontally cut the top of this tuber, he made a lengthwise incision from the amputated top, arranged to receive this shoot conforming to its whistle shape, the thickness of the branch being about the same as that of the tuber's neck.
Thus prepared and carefully tied, this tuber was planted in the open ground. Lacking experience, it suffered some discomforts, which were remedied, and soon the branch of the graft, having elongated, formed a main stem, and another weaker one arose from the graft.
In the autumn, it resulted in a clump less bushy than that from which the shoot was taken. The flowering of the plant was delayed only by fifteen days compared to the mother plant. The flowers of both individuals were similar and very numerous. Its new tubers numbered three. They were elongated and as thick as a little finger, and were adhered to the base of the graft branch. The weld binding this branch to the tuber was as solid as that of a grafted tree. This root, thrown to the ground with force, suffered no breakage.
All the results of the grafting operation are perfectly demonstrated in this section. Here is a very important observation: However old it is, the dahlia resulting from a tuber graft proved to be smaller in size and volume compared to the one that had provided the grafted shoot, although it did not lose any of the merits of the flowering of the mother plant.
"N'est-ce pas là un indice d'un moyen assez naturel à employer pour amoindrir à volonté les dahlias par trop élevés ou trop touffus, et les réduire à des proportions plus convenables?" (Isn't this an indication of a quite natural method we can employ to reduce excessively tall or bushy dahlias to more appropriate proportions at will?)
This observation has not escaped our horticulturists. This reduction method has been greatly perfected. Today, one can reduce a dahlia of excessive height to a third or a half at will, and still enjoy all its beauty on a smaller scale. Here is how one can achieve this goal.
A branch is amputated, and the base of this graft is cut into a flute beak shape (Plate VII, Figure 22 D). Of the two buds it had, only one can remain. The one that was opposite it was removed when shaping the flute beak.
This graft is slid into the slit that has been made on the tuber. The eye [leaf node; ~Ed.] inserted into the tuber will produce roots. The stem of the graft, nourished within the tuber, will strengthen. This obliging tuber may perish, or it may become very large. In this case, it will prevent the natural and proper roots of the graft from quickly forming new tubers.
These delays, difficulties, and obstacles will evidently result in a smaller dahlia, though it precisely represents the variety from which it originated.
A highly distinguished amateur advises grafting in the following manner.
Take a small, well-formed, slightly short, and very healthy tuber. Once the top of the tuber is ennobled [I believe this means that the eye has swelled; ~Ed.] a slit (Plate VI, Figure 21) is made to a depth of a few tenths of an inch in length, and proportionate to the cut made at the base of the graft.
Unable to lift the skin of the tuber as one would the bark of a tree, yet wishing to achieve the same result, use a very fine double-edged blade to cut into the tuber. Cut from top to bottom, on the right and left, the flesh of the tuber that adheres to the epidermis on the edges of the longitudinal slit.
This operation results in a void within the tuber. However, enough flesh remains to appear on the epidermis like the herbaceous layer that is part of the tree's bark. The graft is slid into this void, so perfectly inserted and fitted under these solid coverings, from the bottom to the top end of the incision, that it is not necessarily to tie the graft in place.
The operation of grafting dahlias is an admirable resource in many situations. If one desires to see a dahlia bloom very quickly (which suits daily commerce) one prepares a graft without buttons or collars, with a base as far removed as possible from the two eyes or leaves reserved in its upper part. This completely bare base of the graft will be nourished by the tuber throughout the growing season.
Once the plant's life cycle is complete, the stem dies and the root, not being adhered, is incapable of producing another. Such are most of the dahlias displayed in our markets and sold at low prices. Woe to the trusting public, or insufficiently knowledgeable to recognize at the plant's collar whether it is annual or perennial.
In September or October, if one wishes to quickly obtain a similar specimen of a particularly distinguished dahlia (to which one attaches great importance) one cuts a branch from the plant. The grower immediately grafts it onto a tuber, ensuring it is protected with the utmost care from any accident that could be detrimental at this late season.
To accelerate the overly slow development of roots, one pinches the stem. The sap, thus stopped in its rise, is forced to work in favor of the new tubers, and the acquisition of this fine specimen is quickly ensured.
Should an unforeseen misfortune occur that could lead to an irreplaceable loss (for example, a broken stem), one can remedy this misfortune by grafting rather than cutting. To do this, a wedge-shaped graft is shaped, leaving a strip of “bark” and the two opposite eyes [leaf nodes; ~Ed.] at the base of the graft.
This shoot is inserted into the slit made on a tuber. These two eyes will grow into tuberous roots more quickly than a cutting whose callus would only slowly produce them (say, over the course of a month or six weeks). With the grafting operation, eight days are sufficient to obtain these roots.
Finally, regardless of the method used for propagation using the method described here, one must provide the grafted plant with all the care its condition of weakness demands. Once sufficiently recovered, after about ten days, it can be exposed to open air, but always with caution.
A word of caution: Once one has grafted onto a tuber, if the graft did not have at its lower end an eye from which new tubers could emerge, one should not count on the reproduction of the species for the following year. It is absolutely necessary, according to Mr. Chauvière's opinion, that new tubers emerge from an eye of the species to be propagated.
Thus, the grafts of Plate VI, Figures 16, 17, 18, 19, and 21 will not produce tubers capable of sprouting stems.
However, the variety will not be lost. As soon as the individual has produced shoots, it can be propagated with branches bearing eyes at the lower end. These eyes or buds will form new tubers full of youth and vigor. If they do not flower in that season (which may be too advanced) they will keep very well for the following year.
These young tubers are the best means of preserving dahlias and are far preferable to the division of large plants. Which a grower may forgo if they were to employ this sole method of obtaining tubers.
