Transactions of the Horticultural Society of London, vol 1, 107-111
XVIII. An Account of a Method of hastening the Maturation of Grapes.
In a Letter to the Right Hon. Sir JOSEPH BANKS, Bart. K.B. P.R.S. &c.
By JOHN WILLIAMS, Esq.
Read May 3, 1808.
IT is a fact well known to gardeners, that Vines, when exposed in this climate to the open air, although trained to walls with southern aspects, and having every advantage of judicious culture, in the ordinary course of our seasons ripen their fruit with difficulty. This remark, however, though true in general, admits of some exceptions, for I have occasionally seen trees of the common White Muscadine, and Black Cluster Grapes, that have matured their fruit very well, and earlier by a fortnight or three weeks, than others of the same kinds, and apparently possessing similar advantages of soil and aspect.
The Vines that ripened the fruit thus early, I have generally remarked, were old trees having trunks eight or ten feet high, before their bearing branches commenced. It occurred to me, that this disposition to ripen early, might be occasioned by the dryness and rigidity of the vessels of the old trunk, obstructing the circulation of that portion of the sap, which is supposed to descend from the leaf. And to prove whether or not my conjectures were correct, I made incisions through the bark on the trunks of several Vines growing in my garden, removing a circle of bark from each, and thus leaving the naked alburnum above an inch in width completely exposed; this was done in the months of June and July. The following autumn the fruit growing on these trees came to great perfection, having ripened from a fortnight to three weeks earlier than usual: but in the succeeding spring, the Vines did not shoot with their accustomed vigour, and I found that I had injured them by exposing the alburnum unnecessarily.
Last summer these experiments were repeated: at the end of July and the beginning of August, I took annular excisions of bark from the trunks of several of my Vines, and that the exposed alburnum might be again covered with new bark by the end of autumn, the removed circles were made rather less than a quarter of an inch in width. Two Vines of the White Frontiniac, in similar states of growth, being trained near to each other on a south wall, were selected for trial; one of these was experimented on (if I may use the term), the other was left in its natural state, to form a standard of comparison. When the circle of bark had been removed about a fortnight, the berries on the experimented tree, began evidently to swell faster than those on the other, and by the beginning of September showed indications of approaching ripeness, while the fruit of the unexperimented tree continued green and small. In the beginning of October the fruit on the tree that had the bark removed from it was quite ripe, the other only just began to show a disposition to ripen, for the bunches were shortly afterwards destroyed by the autumnal frosts. In every case in which circles of bark were removed, I invariably found that the fruit not only ripened earlier, but the berries were considerably larger than usual, and more highly flavoured.
The effects thus produced, I can account for only, by adopting Mr. KNIGHT'S theory of the downward circulation of the sap, the truth of which these experiments, in my opinion, tend strongly to confirm. I therefore imagine by cutting through the cortex and liber without wounding the alburnum, that the descent of that portion of the sap which has undergone preparation in the leaf is obstructed and confined in the branches situated above the incision; consequently the fruit is better nourished and its maturation hastened. It is certainly a considerable point gained in the culture of the Vine, to be able to bring the fruit to perfection, by a process so simple, and so easily performed. But lest there should be any misconception in the foregoing statement, I will briefly describe the exact method to be followed by any person, who may be desirous of trying this mode of ripening Grapes. The best time for performing that operation on Vines growing in the open air, is towards the end of July, or beginning of August; and it is a material point, not to let the, removed circle of bark be too wide: from one to two eighths of an inch will be a space of sufficient width; the exposed alburnum will then be covered again with new bark before the following winter, so that there will be no danger of injuring the future health of the tree.
It is not of much consequence in what part of the tree the incision is made, but in case the trunk is very large, I should then recommend, that the circles be made in the smaller branches.
It is to be observed that all shoots which come out from the root of the Vine, or from the front of the trunk situated below the incision, must be removed as often as they appear, unless bearing wood is particularly wanted to fill up the lower part of the wall, in which case one or two shoots may be left.
Grapes growing in forcing houses are equally improved in point of size and flavour, as well as made to ripen earlier by taking away circles of bark: the time for doing this, is when the fruit is set, and the berries are about the size of small shot. The removed circles may here be made wider than on Vines growing in the open air, as the bark is sooner renewed in Forcing Houses, owing to the warmth and moisture in those places. Half an inch will not be too great a width to take off in a circle from a vigorous growing Vine, but I do not recommend the operation to be performed at all on weak trees.
I think that this practice may be extended to other fruits, so as to hasten their maturity, especially Figs, in which there is a most abundant flow of returning sap; and it demonstrates to us, why old trees are more disposed to bear fruit than young ones. MILLER informs us, that the Vineyards in Italy are thought to improve every year by age, till they are fifty years old. It therefore appears to me that nature, in the course of time, produces effects similar to what I have above recommended to be done by art. For, as trees become old, the returning vessels do not convey the sap into the roots, with the same facility they did when young; thus by occasionally removing circles of bark, we only anticipate the process of nature; in both cases a stagnation of the true sap is obtained in the fruiting branches, and the redundant nutriment then passes into the fruit.
I have sometimes found, that after the circle of bark has been removed, a small portion of the inner bark has adhered to the alburnum: it is of the utmost importance to remove this, though ever so small, otherwise in a very short space of time, the communication is again established with the root, and little or no effect produced. Therefore, in about ten days after the first operation has been performed, I generally look at the part from whence the bark was removed, and separate any small portion, which may have escaped the knife the first time.
I am, Sir,
Your obedient humble Servant,
20th April, 1808.