Comfrey is an amazing plant, as medicine, as food, as companion plant, in compost, and in plenty of other ways. Comfrey is not uncommonly grown under fruit trees where its deep roots draw resources from below to the surface where fruit trees can access them.
Comfrey juice, basically (by way of its key chemical allantoin), proliferates cell growth which when dabbed or plastered on flesh wounds causes these wounds to heal quickly, and it has a similar effect on cracked and broken bones.
When injected (allantoin) into flower bulbs as noted below, growth rate and bloom size were sped up and enlarged. One can imagine the possible effect of injecting or possibly even daubing figs with what is essentially comfrey juice. Who knows, might help advance late ripening varieties, or, again, who knows?, might have a fig wasp type effect on fig fruit. Could be no effect, will have to see. I look forward to trying a few things along these lines this summer and fall.
A lot of comfrey plants, though not all, have appeared here, including some weeks ago (weeks ahead of last year). This recent snow and cold doesn’t faze them much, per the photo:
from Comfrey: Past, Present & Future by Lawrence D. Hills, 1976, pages 194-199:
Distribution of Allantoin in the Vegetable Kingdom
Our knowledge of this is not very extensive but it is a very suggestive fact that such analyses as have been made indicate that it [allantoin] is generally found in parts which are related to growth, either active or potential. We have a striking example of this in the Comfrey where it is present in the roots and terminal buds. The leaves have not yet been thoroughly investigated, but the interesting point is the large amount of allantoin in the rhizome, greater than in any plants heretofore investigated. E. Schulze and J. Barbieri  in 1881–82 found it in the buds of certain plants and in the bark of branches of trees and Ackroyd refers to its identification by Richardson Crampton (1886) in the embryos of wheat separated in the process of milling and in beet juice. Ackroyd  demonstrated its presence in bread, french beans and green peas, whereas it is absent in bananas and rhubarb. …
The Comfrey rhizome … in the earliest months of the year (January to March) contains from 0.6 to 0.8 percent of allantoin. Analysed a couple of months later it contains about 0.4 percent. In July the amount is still further diminished and when the plant is in full growth practically none is to be found in the rhizome but it is discoverable in the terminal buds, leaves, and young shoots. This important fact may be regarded as evidence that the plant withdraws allantoin from its storehouse in the rhizome and utilizes it for the purposes of cell-proliferation. …
Experiments with Plants
The presence of allantoin in the underground reserves and growing parts of plants … added to the clinical evidence that it promotes healing in ulcerative conditions which will be referred to later, naturally led to the suggestion that experiments made upon plants might afford some information, confirmatory or otherwise, of its proliferative properties or functions. By my request Mr. Coppin planted a large number of hyacinth bulbs (the growth of which had been started in the dark) in solutions of allantoin varying from 0.1 to 0.5 percent, and it was found that the growth of the roots was inhibited in a ratio proportionate to the amount of allantoin in the solution—that is, the stronger the solution the less was the amount of growth in the root.
Notwithstanding this diminished root growth, which was confirmed by microscopic examination, the flower stems of the plants grew in a stunted way, but none had blossomed at the end of twelve weeks, and it therefore appeared that allantoin did not promote cell-growth when added to the water in which the bulbs were growing, in fact their growth appeared to be retarded. This was disappointing, but an interesting development now ensued. It seemed certain that in plants the allantoin or other proliferative agent is stored for use in the rhizomes, buds, barks and germinal parts, and is probably elaborated there as the result of some metabolic process. There is no allantoin normally in the water or earth in which bulbs are grown, but it or some kindred substance is evidently formed and stored in the bulb or, in the case of other plants, in the rhizomes or roots, to be drawn upon as required for advancing the processes of growth and development. This being the case, the suggestion naturally arose that one might try the effect of injecting a solution of allantoin into the bulbs, and a number of experiments were conducted on these lines, the first of which was made in a more or less casual way as follows:
A child in the Liverpool Royal Southern Hospital had two earth-grown hyacinths in a pot. They had grown quite unequally, one having developed well with the commencement of a flower, the other being feeble, short and showing no signs of blossom.
About 15 minims of allantoin solution (0.4 percent) were injected on several occasions into the bulb of the latter, with the result that rapid growth ensued and it overgrew its more vigorous neighbour, and flowered before it (fig. 1).
This experiment excited the interest of the Sister of the ward (Miss Archer) and of the Matron (Miss Jolly), and they gave similar injections into the bulbs of a considerable number of plants in about equal stages of growth. Controls were used, some being injected with quantities of water equal in amount to the quantities of allantoin solution given, others being grown without and injections; these experiments were conducted in earth-grown bulbs. In addition, some hyacinth bulbs which had just started growth, the shoots being about 1/4 in. high, were planted in water, and some of them were injected every third or fourth day with allantoin solution, some with water only, the remainder being controls, and the same results were obtained in every case. The allantoinevidently acted as a cell-proliferant, forcing the growth of the shoots, and especially of the flowers (for it was noticeable that the plant often blossomed with comparatively little leaf-growth), commonly before their untreated neighbours had reached anything like the stage of flower production. The water-injected plants grew better than the uninjected ones, but nothing like so rapidly as those to which allantoin had been added.
These experiments were repeated many times with tulips (figs. 2, 3 and 4), lilies of the valley and other plants, care being taken to ensure that they were planted at the same time, in the same tubful of earth, and under the same conditions of temperature and surroundings. These results have been confirmed many times, and in the cases of non-bulbous plants the injection of allantoin solution into or below the flower-buds or into the bases of individual spikes has resulted in the production of large flowers contrasting strongly with other untreated flowers or spikes on the same plant (figs. 5 and 6).
In the water-grown plants which were injected it was noted that with the increased growth of the shoots there was sometimes a diminished growth of the roots, which were considerable longer and stronger in the controls.
This led to the impression that perhaps the roots were not so necessary to the plant if its water as well as the proliferant content were kept high, and in order to test this point a number of hyacinth bulbs were selected which had shoots 1/4 in. high but no visible roots. Some of these were injected with allantoin solution, some with water, others being uninjected, and they were simply placed upon a plate without earth or water. At the end of seven or eight days the little shoots of the treated plants were opening out into leaves. The water-injected bulbs also lived, but did not grow so well, whereas the shoots of the controls browned at the tips and shrivelled up. Not a sign of roots made their appearance in any of these plants.
[Photo with caption:] Fig. 1. Hyacinths.—The one on the left was injected with allantoin. It was less in height and feebler than its neighbour on the right at the commencement of the experiment.
[Photo with caption:] Fig. 2. A bowl of tulips.—A central line of the bulbs were injected with allantoin. The marginal ones were not injected. Figs. 2, 3 and 4 show the stages in growth in the two sets.
[Photo of tulips growing, with caption:] Fig. 3.
[Photo of tulips growing, with caption:] Fig. 4.
[Photo with caption:] Fig. 5. Chrysanthemum which was injected on several occasions at the base of the spike of flowers on the left. Showing the advanced inflorescence compared with the portions of the plant which are undergoing normal growth.
[Photo with caption:] Fig. 6. In this chrysanthemum the injections were given into the flower bud of the large bloom when it was at the stage of the unexpanded flower on the right. There was no nipping of the young flower buds to promote large blooms.
From these experiments one gathers the impression that allantoin is a substance which is capable of being utilized by vegetable cells in connection with their proliferative processes, just as there seems to be proof that it has proliferative properties in connection with certain animal cells, if one may judge by the way in which it promotes healing in chronic and acute ulcerative conditions which will be referred to later on. In both cases the reproduced cells are normal microscopically and resemble those from which they took their origin.
In connection with the injection of bulbs a medical man wrote to me many years ago explaining that in repeating my experiments his results were contradictory to those which I had obtained. His plants became stunted and growth was interfered with. On asking for details concerning his experiment it transpired that he had injected his bulbs with an infusion of Comfrey which he had prepared by prolonged boiling of the roots. It is quite probable that the contained allantoin would be decomposed by the boiling, but there is also a possibility that in the root there may be a controlling substance uninfluenced by heat which retards growth. A research concerning this possibility was not proceeded with.