( Originally Published 1942 )
GRAFTING is a very interesting method of propagating plants. It consists of uniting a small piece (scion) of one plant with another rooted plant (stock) . The tissues of the two parts make a perfect union, and the scion continues to grow producing the same type of plant from which it was taken, while the root-stock furnishes the food for that growth.
The root-stock does not alter the original characteristics of the plant which is grafted to it except that it may influence its size, rate of growth and profusion of blooms. The color of the flower, character and disposition of spines and general habit of growth remains just the same as though the scion had been used as a cutting and were growing on its own root system.
The intimate union of plant cells essential to successful grafting will not take place unless both scion and stock are rather closely related. Cacti may be grafted to cacti; Euphorbias may be grafted to Euphorbias; but no matter how much certain Euphorbias may superficially resemble Cacti, they may not be grafted together. Even certain species of cacti are found to be more congenial than others and will unite much more rapidly, and this fact should be considered when selecting stocks for grafting particular species.
Even though grafting does not change the characteristics of the plant, there are some desirable results which may be secured by this process. A species which has sluggish growth and few blooms when grown on its own roots may be grafted on a strong vigorous root-stock that will greatly in-crease both the growth of the plant and the number of blooms. Those cacti which are the despair of the grower because they are so delicately sensitive to adverse soil, moisture or climatic conditions may often be grafted on one of these vigorous sorts that are so hardy that they seem to thrive on neglect. Grafting not only often increases the number of blooms, but in some instances it encourages seed production which is very desirable with those species whose seeds are so difficult to obtain that they are looked upon almost as precious gems.
Nature has established definite rules for the development of living things. Those rules are enforced with such severity that we have generally come to accept them as inflexible—we feel very much as we did as a child when "teacher" laid down rules and regulations that could be violated only at our peril. What child does not have that deeply planted perversity of spirit that thrills with exultation when he discovers some method by which those rules and regulations laid down by "teacher" may be successfully circumvented! We adults have that same perversity of spirit towards Nature and her mandates. Grafting is one means by which we can challenge her authority. Nature decrees that a plant shall grow according to certain definite pre-scribed specifications. We step in with a knife, a scion, skill and knowledge and up-set Nature's specifications and force her to produce a plant very different from that which she intended. Is it any wonder that grafting is so intriguing that its popularity is growing by leaps and bounds irrespective of the practical benefits to be derived from the practice? Much of the cactus grafting is being done just for the pleasure of being able to do it, and it is abundantly justified on that basis even without other considerations. The author, however, is inclined to question the contention of some growers that they can increase the beauty of their plants by grafting. After granting all of the above listed advantages, the author is compelled to admit that when the stock is given equal prominence with the scion the result leaves her appreciation cold. There is an artificiality that does not harmonize with the spirit of the cacti it fails to improve nature, it is merely a built thing. It is for this reason that it is suggested that the union be made so close to the ground that the stock will be inconspicuous if not entirely hidden by the soil, except in those special cases where a longer stock is desired. It is a little difficult to graft cactus very close to the ground, but after the graft is established the plant may be transplanted and placed deeper in the soil so the point of union is covered.
Perhaps the first important question to be answered in approaching the problem of grafting is relative to the season of the year in which the operation may be best performed. In the author's opinion, there is no best season for grafting cacti, because success depends not on the season but on the physical condition of the stock and scion at the time of the operation. It is folly to assume that grafts will "take" if made at a certain season of the year irrespective of the condition of the plants involved. This is true of the budding and grafting of plants other than cacti, and nature is surprisingly consistent in the fundamental principles with which she governs the growth of her plants. Pecans, for example, have long been considered difficult to bud, and a short period of the year was indicated as the only time during which it could be done at all. But we now know that pecans may be budded during any month of the year in which trees and buds of suitable condition may be found, and time is completely wasted attempting to bud trees even during the supposedly favorable season unless both trees and buds are in the proper condition to be worked. It is true, however, that a larger percentage of plants will be found in the desired condition at certain seasons of the year, but the point we wish to emphasize is that we should fix our attention on the condition of the individual plant instead of assuming that the season is the controlling factor, and that grafting at that time must of necessity be successful.
In the grafting of cacti, it is very important that both the stock and the scion be in a vigorous growing condition. The author feels that a great deal of our difficulty in getting grafts to take properly is due to the violation of this first requirement. A plant in growing condition is filled with sap which is almost bursting with the urge to form new tissue. A scion in similar condition is in a receptive mood and aids in a quick adjustment of the mechanism by means of which a free interchange of sap takes place. New tissue is quickly formed, and the normal processes of the plant resumed with the least possible delay. On the other hand, the processes are sluggish in the stock and scion that are in a more or less dormant condition. The cut tissues dry out instead of healing; the contacted cells of the two parts that do not unite immediately soon break down so that they can never grow together; the scion either dies or such an imperfect union is formed that satisfactory growth can never take place. A vigorous stock will often, but not always, overcome the sluggishness of a scion which is not in quite perfect condition. These suggestions should be considered when the grower can choose his own time for grafting and can use his judgment in selecting both stock and scion, but there are times when we are forced by circumstances to work with whatever materials we may have at hand. It is not difficult after a little experience to recognize the condition of stock and scion which makes success reasonably certain, but it is not so easy to know definitely that certain materials which, in our judgment, are not in proper condition to work will not unite satisfactorily. Plant tissues have a habit of doing astonishing things —one is almost tempted to say that the unexpected is the rule. A stem of some rare species may be broken accidentally, a friend may present you with some nice cuttings, you may have a plant that is starting to die —you may be very anxious to graft this material in order to save it. Do not throw it away simply because it does not appear to be in perfect condition according to the specifications of some one else. Try it. Do the very best you can with the material you have available, and many times you will be delightfully surprised at your results.
The species that may be used as stocks are many, but only those are usually chosen which are strong, vigorous growers, adapt themselves to a wide variety of soils, and may be propagated easily and rapidly by cuttings. Various species of Cereus seem to be the most popular as they meet these general requirements very nicely. When it is desired to make the graft a considerable distance above the ground as is usually done in grafting the rat-tail cactus (Cereus flagelliformis) and similar species, the species that have the robust, upright form of growth such as C. stellatus and C. serpentinus are more generally used. The weaker stemmed forms such as C. nycticalis, C. tortuosus, C. grandi f torus, etc., are often used when the graft is to be made close to the ground.
A stock that is too young has such tender tissues that they dry out excessively when grafted, and so is not satisfactory. An old stock may have a woody core which makes it very difficult to work. A little experience will teach the beginner to select stocks that are between these two extremes.
The only tool needed in making grafts is a knife, but the type of knife used and its condition is very, very important. It is a matter of common knowledge that the healing of a wound in animal tissues from a dull knife is a long and painful process often attended by real danger of infection. The surgeon insists that all cutting tools shall be as sharp as it is possible to have them, because the sharper the knife the fewer cells ruptured and the more rapid the healing process. The same principle obtains in plant surgery. The ideal would be to have a tool so sharp that a cut could be made without disrupting more than a single layer of cells. Tissues so cut would heal with scarcely a break in their growth. This is, of course, quite impossible because a cell is so small that only when very greatly magnified can it be seen. But when a large number of layers of these cells are broken and torn by a dull or clumsy tool, the sap within this mass of ruptured cells becomes stagnant, sour—not only devoid of life but destroying life, spreading putrefaction. The uniting of living tissues is a delicate process, and no one should be surprised at their failure to unite under unfavorable conditions as described above.
The knife, then, should be as sharp as it can be made with as smooth an edge as it is possible to attain. It should be sharpened on a fine-grained stone, and it is desirable that the edge be smoothed on a razor hone or strop.
The blade of the knife should be thin as well as sharp, because the thick blade has a tendency to break the cells apart instead of cutting them—it splits the tissues much as a wedge does in splitting logs.
The most useful and satisfactory cutting tool that the author has ever found is a safety-razor blade. Its thinness and sharpness recommend it highly for this purpose. It may be used by holding in the hand, or it may be attached to one of the numerous handles made for that purpose and now on the market.
The knife blade should be kept clean and free from rust. Foreign substances on the blade such as dirt, dried plant juices or rust make the surface rough, and any roughness lacerates the cells unnecessarily during the cutting process. Danger of infection from the knife blade has probably been over-emphasized where normally healthy stocks and scions are being worked. Frequent sterilizing of the knife will do no harm, but the writer feels that mechanical cleanliness is by far the more important. If the blade is carefully wiped off after each operation, it will be quite sufficient so long as none of the plants that are worked are suspected of being diseased.
The most commonly used type of graft when the diameter of the stock is greater than the diameter of the scion is known as the cleft graft. It is very simple, easily made, and seems to give satisfactory results. The stock is cut off at the height at which it is desired to have the new plant develop. It is well not to forget that if the scion is inserted into the stock ten inches above the ground, that point of union will always re-main ten inches above the ground no matter what age or size the plant attains.
A long V-shaped notch is cut in the top of the stock. It is a serious mistake to make this notch too shallow. The width of the notch at the top should be the same as the diameter of the scion to be used. Its depth should be at least one and one-half times the diameter of the scion, and two times the diameter is not too deep. It is not desirable to have the scion longer than is necessary to work nicely. If its length is four or five times its diameter, it is plenty long enough for making this type of graft, and even shorter ones may be worked. One end of the scion must be a growing tip, and the other end is cut in the form of a wedge which will fit accurately into the notch al-ready described. The length and width of both the wedge and notch should be as nearly the same as it is possible to make them. Much of your success will be measured by your skill in cutting the stock and scion to a perfect fit. All of the cut faces should be perfectly flat planes, and not curved or irregular surfaces. It will be found easier if the cuts are made with a smooth, continuous stroke of the knife—drawing the blade through the tissues in-stead of trying to push it through. The wedge-shaped end of the scion is now fitted in the notch of the stock. In order to keep the scion from slipping out of place, it is necessary to fasten it securely. This is done by pinning it with the long needle-like spines of Opuntia or Pereskia. The spines are thrust through the top of the stock so that they pass through the wedge of the scion. In order to keep the sides of the notch from spreading, it is good practice to wrap a cotton string gently but firmly about the top of the stock. This gentle pressure will also help to bring the tissues into more intimate contact and exclude the air more completely. No wax is necessary in making this graft, but the plant should not be exposed to direct sunlight. If either stock or scion is not in the best of condition so you feel that the graft will be slow in taking, it will be helpful to conserve the moisture in both scion and stock by reducing evaporation. This can be done by placing in a more humid atmosphere as is secured by inverting a glass jar over the plant.
It is sometimes desirable to use the saddle graft when the scion to be used has a greater diameter than the stock. This graft is simply the reverse of the cleft graft. The top of the stock is cut in the shape of a wedge, and the notch is made in the scion. Otherwise the procedure is the same and need not be discussed here.
A somewhat different method must be employed in grafting small, globose or thick plants such as Echinocactus, Echinocereus and Mammillaria. The stock and scion should be of nearly the same diameter. The plant to be used as a stock is cut off so as to make a smooth, flat, horizontal surface. The scion is then cut so that the upper end of it has the growing tip, and the lower end is also a smooth, flat surface. The two surfaces are then placed together and may be kept from slipping by pinning with thorns. They should then be firmly tied together with cotton string until growth has started.
Propagating cacti by means of cuttings is a very common practice. Many species are so easily grown in this way that success is assured no matter how crude the method followed. However, a clear understanding of the principles involved and an adjustment of methods to conform to those principles will make it possible not only to obtain a quicker and more satisfactory growth from the plants which grow more easily from cuttings, but it will increase the number of species which may be reproduced in this way.
A cutting is a fragment of a plant which is forced to produce its roots and become a complete individual plant.
It requires considerable time for a cutting to produce roots. The stem has been producing vegetative growth; the whole cell structure is arranged into a mechanism for the production of the tissue which goes to make up the stem-tissue which is quite different in structure and function from the root tissue which it is now called upon to build. It may be said that Nature has made up Her mind to produce a certain type of growth in the stem, and, if you would change Her mind, you must diplomatically supply those conditions which will induce Her to do so.
The cutting should be made with a very sharp knife as recommended in the making of grafts. But, even though a sharp knife be used, the cut surface with its abundant moisture and mass of tender cells presents an ideal condition for the growth of fungus and bacterial diseases. Disease germs are present in practically all soil, and, when a freshly cut surface is placed in direct contact with such soil, infection is almost certain to take place. This is avoided by exposing the cut surface to the sun for several hours or even days if need be, until the cut surface has not only been dried but has become so perfectly sealed by the toughened cell walls that no germ can gain entrance to the tender, juicy tissues beneath.
After this drying is completed, the cutting is ready to be planted. The soil may be the same as recommended for seedlings except that the amount of garden soil may be reduced or left out entirely if it is intended to transplant the cuttings soon after they are well established. The use of Semesan to sterilize the soil should not be neglected. The cutting may put out roots even if the soil is very dry, but more uniform success will result if the soil has just a hint of moisture for the first few weeks. Water should not come in direct contact with the cut surface during this time—it may even be injurious. It is the humidity of the air within the soil coming in contact with the cut surface which induces the roots to start growth. After growth has once started, the moisture content may be gradually increased. Cuttings should not be planted too deeply. It is sufficient to put the cut end only slightly below the surface of the soil.
Plants which have jointed stems, root more readily at the joints than elsewhere, and it is well to take advantage of this fact whenever possible by cutting them at this point. Young side shoots of the plant are also very desirable for this type of propagation, and they may often be used without seriously disfiguring the mother plant.