This section is from the book "The Gardener V3", by William Thomson. Also available from Amazon: The New Organic Grower: A Master's Manual of Tools and Techniques for the Home and Market Gardener.
We now come to treat of the art of grafting, which in passing we may remind the reader is of very great antiquity. Although we cannot definitely say to whom the honour of first introducing it belongs, yet we nevertheless know that it was practised to some extent by the ancients; but from all we can gather from the writings of these periods, it would appear to have been but very imperfectly understood and acted upon. It is referred to by Aristotle and Pliny, as well as several of their contemporaries, but must have been practised more from curiosity, and to afford amusement, than from any benefit they expected to derive from the unions made by them between scion and stock. How far they succeeded in obtaining practical results from the unions made, we have been unable to ascertain; yet we have no sanguine hopes that the results were great. It is a pleasure to us, however, to be able to look back through the dark vista of two thousand years to the cradle-days of a science which is of so much benefit to the gardening world of the present time.
There are various modes of grafting, but it is purposed to make reference only to that mode of it which is in most general use for the Pear when young, and which is known as whip-grafting, or, as it is sometimes called, tongue or splice grafting. Having in our arrangements generally spoken of the Quince stock before the Pear stock, we shall treat it first; for although the mechanical operation in both cases is the same, yet the after-treatment varies to some extent. We shall surmise that the stocks to be worked have been well grown, and are not less than 1 1/2 inches in circumference, and have been headed over in winter to about 6 inches. The scions we also expect to have been selected from the desired sorts at the pruning season, and that all the best ripened and strongest of the wood has been reserved for this purpose. This mode of grafting is invariably done in spring - from the middle of March to the middle of April - but the state of both scion and stock, as well as the other attending circumstances, must all bear more or less upon the time when it ought to be done.
As a general rule, we find the first week in April to suit as well as, if not better than, any time prior to this date, as, generally speaking, the stock is beginning to be pretty active, while the scion is still in a dormant or semi-torpid condition, and these we consider the conditions upon which the greater amount of success depends. This is the very reason which induces us not to transplant stocks the year of grafting, as, being established in the ground, they are easier and more quickly excited when spring comes, and consequently are just as far ahead of the graft as is necessary to insure success. If the stock had been transplanted prior to this operation, the check sustained would have to be overcome, and the tree would be longer in showing signs of active vegetation. At the very least, there ought to be a week between the stock and the scion, and in proof of this we may refer the reader to what Dr Lindley has said upon this point, and which in practice we find to be correct. At page 339 of his 'Theory of Horticulture,' he says: -
The scion should be more backward in its vegetation than the stock, because it will then be less excitable, otherwise its buds 'may begin to grow before a fitting communication is established between the stock and scion, and the latter will be exhausted by its own vigour; if, on the contrary, the stock is in a state of incipient growth, and the scion torpid, cellular granulations will have time to form and unite the wound, and the scion will become distended with sap forced into it from the stock, and thus be able to keep its buds alive when they begin to shoot into branches. In order to assist in this part of the operation, a 'heel' is sometimes in difficult cases left on a scion, and inserted into a vessel of water, until the union has taken place; or, for the same purpose, the scion is bound round with loose string or linen, with one end steeped in water, so as to secure a supply of water to the scion, by the capillary attraction of such a bandage. Indeed, the ordinary practice of surrounding the scion and stock at the point of contact with a mass of grafting clay, is intended for the same purpose - that is to say, to prevent evaporation from the surface of the scion, and to afford a small supply of moisture; and hence, among other things, the superiority of clay over the plasters, mastics, and cements occasionally employed, which simply arrest perspiration, and can never assist in communicating aqueous food for the scion.
Indeed, the whole secret of success depends upon attending to these few simple facts - facts so simple that "he who runs may read," learn, and put into practice with the greatest of confidence.
Almost every one has a mixture of his own, which he terms grafting-wax or grafting-clay, with which he covers over the union between the scion and the stock. Last spring we grafted a considerable number of Apples, and used nothing else than clay got at a brickwork near by, and which had been well "milled," and rendered as plastic as butter; this we found to answer admirably, as the result proved equal to our anticipations. Most people, however, introduce some foreign substance, which has a tendency to prevent cracking. This, however, is not necessary if the clay is covered with moss and moistened two or three times a-week by a watering-pot with a fine rose. I intend, however, this spring, when grafting, to introduce a little of the combings of horses, which, I believe, will make it even unnecessary to use moss. Mr Thomson, in the 'Gardener's Assistant,' recommends "two parts of clayey loam and one part of cow-dung free from litter . . . with some fine short tough hay mixed and beaten up with the cow-dung and clay." Others use horse-dung and clay, while another party uses a combination of all the three, which we believe to be the best where a mixture is made, as the horse-dung will, to a certain extent, prevent cracking, while the cow-dung will render the whole more plastic where the clay is inclined to be loamy.