FERTILIZERS FOR GRAPES
As regards fertilizers, the grape-grower has much to learn and in learning he must approach the problem with humility of mind. For in his experimenting, which is the best way to learn, he will no sooner arrive at what seems to be a certain conclusion, than another season's results or the yields in an adjoining vineyard will upset the findings of past seasons and those obtained in other places. Unfortunately, there is little real knowledge to be obtained on the subject, for grape-growers have not yet broken away from time-worn dictums in regard to fertilizers and still follow recommendations drawn from work with truck and field crops. This is excused by the fact that there have been almost no comprehensive experiments in the country with fertilizers for grapes.
No fallacies die harder than the pronouncements of chemists a generation ago that fertilizing consists in putting in the soil approximately that which the plants take out; and that the chemical composition of the crop affords the necessary guide to fertilizing. These two theories are the basis of nearly every recommendation that can be found for the use of fertilizers in growing crops. The facts applied to the grape, however, are that the average tillable soil contains a hundred or a thousand times more of the chemical constituents of plants than the grape can possibly take from the soil; and many experiments in supplying food to plants show that the chemical composition of the plant is not a safe guide to their fertilizer requirements. Later teachings in regard to the use of fertilizers are: That the quantity of mineral food in a soil may be of far less importance than the quantity of water, and that the cultivator should make certain that there is sufficient moisture in his land so that the mineral salts may be readily dissolved and so become available as plant-food; that far too much importance has been attached to putting chemicals in the soil and too little to the physical condition of the soil, whereby the work of bacteria and the solvent action of organic acids may make available plant-food that without these agencies is unavailable.
These brief and simple statements introduce to grape-growers some of the problems with which they must deal in fertilizing grapes, and show what a complex problem of chemistry, physics and biology fertilizing the soil is; how difficult experimental work in this field is; and how cautious workers must be in interpreting results of either experiment or experience. An account of an experiment in fertilizing a vineyard may make even more plain the difficulties in carrying on experiments in fertilizing fruits and the caution that must be observed in drawing conclusions.
The New York Agricultural Experiment Station is experimenting with fertilizers for grapes at Fredonia, Chautauqua County, the chief grape region in eastern America. The experiment should be of interest to every grape-grower from several points of view. It not only shows that there are many and difficult problems in fertilizing grapes, but also the results of the use of manure, commercial fertilizers and cover-crops in a particular vineyard; it suggests the fertilizers to be used and the methods of use; and it furnishes a plan for an experiment by grape-growers who want to try such an experiment and draw their own conclusions. An account of the experiment and the results for the first five years follows:[10]
"In the vineyard at Fredonia eleven plats were laid out in a section of the vineyard where inequalities of soil and other conditions were slight or were neutralized. Each plat included three rows (about one-sixth of an acre) and was separated from the adjoining plats by a 'buffer' row not under test. One plat in the center of the section served as a check, and five different fertilizer combinations were used on duplicate plats at either side of the check. Plats 1 and 7 received lime and a complete fertilizer with quick-acting and slow-acting nitrogen; Plats 2 and 8 received the complete fertilizer but no lime; on Plats 3 and 9 potash was omitted from the complete fertilizer combination; Plats 4 and 10 received no phosphorus; Plats 5 and 11, no nitrogen; and Plat 6 was the check. The materials were applied at such rates that they provided for the first year 72 pounds of nitrogen per acre, 25 pounds of phosphorus and 59 pounds of potassium; and for each of the last four years two-thirds as much nitrogen and phosphorus and eight-ninths as much potassium. The lime was applied the first and fourth years in quantity to make a ton to the acre annually. Cover-crops were sown on all plats alike and were plowed under in late April or early May of each year. These differed in successive years, but included no legumes. The crops used were rye, wheat, barley and cow-horn turnips separately and the last two in combination.
"The cultivation differed only in thoroughness from that generally used in the Belt, the aim being to maintain a good dust mulch during the whole growing season. Pruning by the Chautauqua System was done throughout by one man, who pruned solely according to the vigor of the individual vines and left four, two or three, or no fruiting canes as appeared best. The vineyard was thoroughly sprayed, all plats alike.
"Low winter temperatures, affecting immature wood and buds caused by unfavorable weather of the previous season, reduced yields materially during two of the five years, and practically neutralized any anticipated benefit from fertilizers. Following the first of these low-crop years, came a season, 1911, in which favorable conditions, acting upon vines left undiminished in vigor by the light crop of the previous year resulted in heavy and quite uniform yields on all the plats.
"The yields for the five years are shown in Table I; and a summary showing the average gains from each treatment is given in Table II, with the average financial balance after deducting the cost of fertilizer application from the increased returns from the plats receiving them.
Table I.—Yield of Grapes (Tons per Acre) in Fertilizer Experiments
| Plat. No. | 1909 | 1910 | 1911 | 1912 | 1913 | 5-year average | |
|---|---|---|---|---|---|---|---|
| Tons | Tons | Tons | Tons | Tons | Tons | ||
| 1 | Complete fertilizer; lime | 4.48 | 2.10 | 5.37 | 3.46 | 2.14 | 3.51 |
| 2 | Complete fertilizer | 4.76 | 2.21 | 5.71 | 4.30 | 2.83 | 3.96 |
| 3 | Nitrogen and phosphorus | 5.17 | 2.14 | 5.61 | 4.00 | 2.25 | 3.83 |
| 4 | Nitrogen and potash | 4.25 | 2.55 | 5.64 | 4.10 | 2.85 | 3.87 |
| 5 | Phosphorus and potash | 3.41 | 2.00 | 5.44 | 4.35 | 1.78 | 3.39 |
| 6 | Check | 3.38 | 2.10 | 5.32 | 3.60 | 1.24 | 3.12 |
| 7 | Complete fertilizer; lime | 4.69 | 2.38 | 5.62 | 4.80 | 3.04 | 4.10 |
| 8 | Complete fertilizer | 4.66 | 2.07 | 5.71 | 4.98 | 2.72 | 4.02 |
| 9 | Nitrogen and phosphorus | 4.99 | 2.04 | 5.35 | 4.89 | 2.61 | 3.97 |
| 10 | Nitrogen and potash | 4.79 | 2.26 | 5.91 | 4.89 | 3.07 | 4.18 |
| 11 | Phosphorus and potash | 4.99 | 1.87 | 5.03 | 4.21 | 1.97 | 3.61 |
Table II.—Average Increase in Grape Yields and Average Financial Gain from Fertilizer Applications
N = nitrogen, P = phosphorus, K = potassium, Ca = lime.
Gains in tons per acre.
| N, P, K, Ca. | N, P, K. | N, P. | N, K. | P, K. | |
|---|---|---|---|---|---|
| Tons | Tons | Tons | Tons | Tons | |
| First plat of pair | 3.51 | 3.96 | 3.83 | 3.87 | 3.39 |
| Second plat of pair | 4.10 | 4.02 | 3.97 | 4.18 | 3.61 |
| Average | 3.80 | 3.97 | 3.90 | 4.02 | 3.50 |
| Check plat | 3.12 | 3.12 | 3.12 | 3.12 | 3.12 |
| Average gain | .68 | .85 | .78 | .90 | .38 |
| Average financial gain | $5.82 | $13.84 | $14.05 | $18.54 | $6.99 |
From this last table the benefit from nitrogen appears quite evident since every combination in which it appears gives a substantial gain over the one from which it is absent. Phosphorus and potassium without the nitrogen, lead to only a slight increase over the check; and lime appears to be of no benefit. Financially, the complete fertilizer and lime combination, the nitrogen and phosphorus combination and the phosphorus and potassium combination failed to pay their cost in five of the ten comparisons; the complete fertilizer was used at a loss four times out of ten; and the nitrogen and potassium combination three times out of ten. Lime had no appreciable effect on either vines or fruit.
"No effect of the fertilizers on the fruit itself, aside from yield, was shown for the first three years; but in 1912, and even more markedly in 1913, the fruit from the plats on which nitrogen had been used was superior in compactness of cluster, size of cluster and size of berry. In 1912 also, when early ripening was a decided advantage, the fruit on the nitrogen plats matured earlier than that on the check plats. In 1913 the favorable ripening season and the smaller crop tended to equalize the time of ripening on all plats. The grapes on the phosphorus-potassium plats were better in quality than those in the check plats but not as good as those on the plats where nitrogen was used.
"Other indexes also show plainly the benefit from nitrogen in this vineyard; for size and weight of leaf, weight of wood produced and number of fruiting canes left on the vines were all greater where fertilizers, and particularly nitrogen, had been used. The three-year averages (1911–1913) of the measurements for these characteristics are shown in Table III:
Table III.—Comparative Production of Leaves, Wood and Fruiting Canes on Grape Vines Differently Fertilized
(Averages for three years.)
| Fertilizer Application | Leaf Weight[11] | Wood Pruned[12] | Fruiting Canes Left[13] |
|---|---|---|---|
| Grams. | Lbs. | ||
| Complete fertilizer; lime | 1,033 | 1,295 | 2,468 |
| Complete fertilizer | 1,010 | 1,367 | 2,609 |
| Nitrogen and phosphorus | 1,047 | 1,272 | 2,585 |
| Nitrogen and potassium | 1,069 | 1,401 | 2,646 |
| Phosphorus and potassium | 964 | 1,086 | 2,326 |
| Check | 930 | 915 | 2,110 |
"In order to secure information as to the behavior of fertilizers on the different soils of the Grape Belt, coöperative tests were carried on in six vineyards owned, respectively, by S. S. Grandin, Westfield; Hon. C. M. Hamilton, State Line; James Lee, Brocton; H. S. Miner, Dunkirk; Miss Frances Jennings, Silver Creek; and J. T. Barnes, Prospect Station. The soil in these vineyards included gravelly loam, shale loam and clay loam, all in the Dunkirk series, and the experiments covered from two to two and a half acres in three cases and about five acres in each of the other vineyards. The work continued four years in all but one of the experiments, which it was necessary to end after the second year.
"The general plan of the tests was much like that at Fredonia in most of the vineyards, with the additions of plats for stable manure and for leguminous and non-leguminous cover crops with and without lime. From two to six check plats were left for comparison in each vineyard. As already stated the results were often inconsistent in duplicate plats in the same vineyard, and if one test appeared to point definitely in a certain direction, the indication would be negatived by results in other vineyards. In these experiments the yield of fruit was the only index to the effect of treatments as it was not possible to weigh leaves or pruned wood, or to count the canes left.
"Nitrogen and potassium in combination, which gave the largest gains and greatest profit in the Station vineyard at Fredonia, showed a 13 per ct. increase in yield on one plat in the Jennings vineyard and a 9 per ct. decrease on the other; in the Miner vineyard this combination apparently resulted in a 25 per ct. increase; in the Lee vineyard in a 21/2 per ct. loss; in the Hamilton vineyard a 17 per ct. gain; and in the Grandin vineyard neither gain nor loss. In only two of the five vineyards in which this combination was tested was the gain great enough to pay the cost of the fertilizer applied. Similar discrepancies, or absence of profitable gain, mark the use of the other fertilizer combinations.
"Even stable manure, the standby of the farmer and fruit-grower, when applied at the rate of five tons per acre each spring, and plowed in, did not, on the average, pay for itself. Indeed, there were few instances among the 60 comparisons possible, in which more than a very moderate profit could be credited to manure. The average increase in yield following the application of manure alone was less than a quarter of a ton of grapes to the acre; while the use of lime with the manure increased the gain to one-third of a ton per acre. The ton of lime to the acre annually would not be paid for by the gain of 175 pounds of grapes. Cover-crops were used in five of the six coöperative experiments and proved even less adapted to increasing crop yields than did the manure. There was no appreciable gain, on the average, from the use of mammoth clover; indeed, a slight loss must be recorded for the clover except upon the plats which were also limed, and even with the lime the average yields on check plats and mammoth clover plats differed by only one one-hundredth of a ton. Wheat or barley with cow-horn turnips made a slightly better showing, as the plats on which these crops were turned under, without lime, averaged about one-twentieth of a ton to the acre better than the checks. With these non-legumes, lime was apparently a detriment, as the plants with the lime yielded a tenth of a ton less, on the average, than those without it."
From this experiment it becomes clear that the use of fertilizers in a vineyard is a local problem. General advice is of little value. It is evident also that the fertilization of vineyards is so involved with other factors that only carefully planned and long continued work will give reliable information as to the needs of vines. Indeed, field experiments even in carefully selected vineyards, as the coöperative experiments show, may be so contradictory and misleading as to be worse than useless, if deductions are made from the results of a few seasons. The experiment, however, has brought forth information about fertilizing vineyards that ought to be most helpful to grape-growers. Thus, the results suggest:
It is usually waste to make applications of fertilizers in poorly drained vineyards, in such as suffer from winter cold or spring frosts, where insect pests are epidemic and uncontrolled or where good care is lacking. The experiments furnish several examples of inertness, ineffectiveness or failure to produce profit when the fertilizers were applied under any of the conditions named. They emphasize the importance of paying attention to all of the factors on which plant growth is dependent. Moisture, soil temperature, aëration, the texture of the soil, freedom from pests, cold and frosts, as well as the supply of food may limit the yield of grapes.
It is certain in some of the experiments and strongly indicated in others that the soil is having a one-sided wear—that only one or a very few of the elements of fertility are lacking. The element most frequently lacking is nitrogen. Exception will probably be found in very light sands or gravels which are often deficient in potash and the phosphates; or on soils so shallow or of such mechanical texture that the root range of the vine is limited; or in soils so wet or so dry as to limit the root range or prevent biological activities. These exceptions mean, as a rule, that the soils possessing the unfavorable qualities are unfitted for grape-growing. The grape-grower should try to discover which of the fertilizing elements his soil lacks and not waste by using elements not needed.
The marked unevenness of the soil in the seven vineyards in which these experiments were carried on, as indicated by the crops and the effects of the fertilizers, furnishes food for thought to grape-growers. Maximum profits cannot be approached in vineyards in which the soil is as uneven as in these, which were in every case selected because there was an appearance of uniformity. A problem before grape-growers is to make uniform all conditions in their vineyards, and the vines must be kept free from pests if fertilizers are to be profitably used.
A grape-grower may assume that his vines do not need fertilizers if they are vigorous and making a fair annual growth. When the vineyard is found to be failing in vigor, the first step to be taken is to make sure that the drainage is good; the second step, to control insect and fungous pests; the third, to give tillage and good care; and the fourth step is to apply fertilizers if they be found necessary. Few vineyards will be found to require a complete fertilizer. What the special requirements of a vineyard are can be ascertained only by experiment and are probably not ascertainable by analyses of the soil. This experiment furnishes suggestions as to how the grape-grower may test the value of fertilizers in his own vineyard.
When it is certain that vines need fertilization, and what is wanted is known, the fertilizers should be put on in the spring and be worked in by the spring cultivation. Stable manure should be plowed under. Grape roots forage throughout the whole top layer of soil so that the land should be covered with the fertilizer, whether chemical or barnyard manure. Applications of commercial fertilizers are generally spread broadcast, though it is better to drill them in if the foliage is out on the vines and thus avoid possible injury to tender foliage. Commercial fertilizers should be mixed thoroughly and in a finely divided state. In leachy soils, nitrate of soda ought not to be applied too early in the season, as it will quickly wash down out of reach of the grape roots.
Some soils are too rich for the grape. On these the growth is over-luxuriant, the wood does not mature in the autumn, fruit-buds do not form and the fruit is poor in quality. Certain varieties can stand a richer soil than others. Over-richness is a trouble that may cure itself as the vines come in full bearing and make greater demands on the soil for food. It is well, however, on a soil that is suspected of being too rich or so proved by the behavior of the vines, to provide an extra wire on the trellis, to prune little and thus take care of the rampant growth. Some soils, however, and this is often the case, are so rich that the grape cannot be made to thrive in them; the vines waste their substance in riotous living, producing luxuriant foliage and lusty wood but little or no fruit.
PRUNING THE GRAPE IN EASTERN AMERICA
The inexperienced look on pruning as a difficult operation in grape-growing. But once a few fundamentals are grasped, grape-pruning is not difficult. There is much less perplexity in pruning the grape than in pruning tree-fruits. Pruning follows accepted patterns in every grape region, and when the pattern is learned the difficulties are easily overcome. The inexperienced are confused by the array of "principles," "types," "methods," "systems" and the many technical terms that enter into discussions of grape-pruning. Some of the technicalities come from European practices, and others originated in the infancy of grape-growing in this country when there was great diversity in pruning. Divested of much that is but jargon, an inexperienced man can easily learn in a few lessons, from word of mouth or printed page, how to prune grapes.
The simplicity of pruning has led to slighting the work in commercial vineyards, by too often trusting it to unskilled hands. Then, too, in this age of power-propelled tools, pride in hand labor has been left behind, and few grape-growers now take time and trouble to become expert in pruning. Simple as the work may seem to those long accustomed to it, he who wants to put into his pruning painstaking intelligence and to taste the joy of a task well done finds in this vineyard operation an ample field for pleasure and for the development of greater profits. The price to be paid by those who would thus attempt perfection in pruning the vine is forward vision, the mechanic's eye, the gardener's touch, patience, and pride in handicraft.
Simple as pruning is, the pruner soon learns that it is an art in which perfection is better known in mind than followed in deed. The theory is easy but there are some stumbling blocks to make its consummation difficult. It is an art in which rules do not suffice, for no two vineyards can be pruned alike in amount or method, and every grape-grower finds his vineyard a proper field for the gratification of his taste in pruning. Happily, however, enlightened theory and sound practice are in perfect accord in grape-pruning, so that specific advice is well founded on governing principles.
One cannot, of course, learn to prune unless he understands the habit of the grape-vine and is familiar with the terms applied to the different parts of the vine. As a preliminary to this chapter, therefore, knowledge of Chapter XVII, in which the structure of the grape-vine is discussed, is necessary. The next step is to distinguish between pruning and training.
The grape is pruned to increase in various ways the economic value of the plant by increasing the quantity and value of the crop. This is pruning proper. Or grapes are pruned to make well-proportioned plants with the parts so disposed that the vines are to the highest degree manageable in the vineyard. This is training. To repeat, the grape-plant is pruned to regulate the crop; it is trained to regulate the vine. Grape-growers usually speak of both operations as "pruning," but it is better to keep in mind the two conceptions. The distinctions between pruning and training must be made more apparent by setting forth in greater detail the results attained by the two operations.
Proper pruning of vines in their first year in the vineyard, which, as we have seen, consists of cutting the young plants back severely, brings the vines in productive bearing a year or two years earlier than they would have borne had the pruning been neglected. This early pruning, since it is done with an eye to the vigor of each vine, insures greater uniformity in the growth and productiveness of the vineyard. Uniformity thus brought about is important not only for the time being, but for the future development of the vines, since weak vines, if unpruned, are stunted and may require years to overtake more vigorous vines in the vineyard.
The quality of the crop may be regulated by pruning. When vines bear too heavily, the grapes are small, and wine-makers have found that they seldom develop sugar and flavor as do grapes on vines not over-bearing. Grapes on vines too heavily laden seldom ripen or color well. Not only are the grapes on poorly pruned and unpruned vines poor in quality but the grapes on such vines are usually not well distributed and therefore ripen and color unevenly. The results just mentioned follow because the bunches in a poorly distributed crop receive varying amounts of light and heat depending on the distance from the ground, the distance from the trunk and on the amount of shade.
Pruning may be used to regulate the quantity of grapes borne in a vineyard and so be made somewhat helpful in preventing alternate bearing. Abnormally large crops are usually followed by partial crop failure and biennial bearing sometimes sets in, but the large crop may be reduced by pruning and the evil consequences wholly or partly avoided. It follows that pruning must depend much on the vigor of the vine; for a weak vine may be so pruned as to cause it to overbear; and, on the other hand, a vigorous vine pruned in the same way might not bear at all.
It is necessary to regulate the shape of the vine by training so that tilling, spraying, pruning and harvesting can be easily performed and the crop be kept off the ground. The cost of production is always less in a well-pruned vineyard because all vineyard operations are more easily carried out.
The life of a vineyard is lengthened when the vines are well trained, because when the parts of a vine are properly disposed on trellis or stake the plants are less often injured in vineyard operations. Moreover, not infrequently vines die from over-production and consequent breaking of canes or trunks which might have been prevented by pruning to shape the vine. Suckers and water-sprouts are less common on well-trained vines. It is necessary, too, by training to keep the bunches away from trunk, canes and other bunches and so prevent injury to the grapes.
Lastly, fashion, taste or a more or less abnormal use of the grapes, may prescribe the form in which a vine is trained. Fashion and taste run from very simple or natural styles to exceedingly complex, formal ones, depending, often, on the variety, the environment or other condition, but just as often on the whim of the grape-grower. The grape is a favorite ornamental for fences, arbors and to cover buildings; for all of these purposes the vines must be trained as occasion calls.
Leaving the shaping of the plant out of consideration and having in mind pruning proper, all efforts in pruning are directed toward two objects: (1) The production of leafy shoots to increase the vigor of the plant. (2) The promotion of the formation of fruit-buds. The first, in common parlance, is pruning for wood; the second, pruning for fruit.
Some grapes, in common with varieties of all fruits, produce excessive crops of fruit so that the plants exhaust themselves, to their permanent injury and to the detriment of the crop. Something must be done to restore and increase vegetative vigor. The most natural procedure is to lessen the struggle for existence among the parts of the plant. The richer and the more abundant the supply of the food solution, the greater the vegetative activity, the larger the leaves and the larger and stouter the internodes. Obviously, the supply of food solution for each bud may be increased by decreasing the number of buds. The weaker the plants, therefore, the more the vine should be cut. The severe pruning in the first two years of the vine's existence is an example of pruning for wood. The vine is pruned for wood in the resting period between the fall of leaf and the swelling of buds the following spring.
Growers of all fruits soon learn that excessive vegetative vigor is not usually accompanied by fruitfulness. Too great vigor is indicated by long, leafy, unbranching shoots. Some fruit-growers go so far as to say that fruitfulness is inversely proportionate to vegetative vigor. There are several methods of diminishing the vigor of the vine; as, withholding water and fertilizers, stopping tillage, the method of training and by pruning. Pruning is used to decrease the vigor of the vine, in theory at least, for the practice is not always so successful, by pruning the roots or by summer-pruning the shoots.
Root-pruning the grape at intervals of several years is a regular practice with some varieties in warm countries, Europe more especially, but is seldom or never practiced in America except when planting and when roots arise from the cion above the union of stock and cion.
Summer-pruning to induce fruitfulness consists in removing new shoots with newly developed leaves. These young shoots have been developed from reserve material stored up the preceding season, and until they are so far developed that they can perform the functions of leaves they are to be counted as parasites. When, therefore, these shoots are pruned or pinched away, the plant is robbed of the material used by the lusty shoot which up to this time has given nothing in return. The vigor of the plant is thus checked and fruitfulness increased. Summer-pruning may become harmful if delayed too long. The time to prune is past with the grape when the leaves have passed from the light green color of new growth to the dark green of mature leaves.
Fruit-bearing may be augmented by bending, twisting or ringing the canes, since all of these operations diminish vegetative vigor. Ringing is the only one of these methods in general use, and this only for some special variety or special purpose, and usually with the result that the vigor of the vine is diminished too much for the good of the plant. Ringing is discussed more fully in Chapter XVI.
Before attempting to prune, the pruner must understand precisely how the grape bears its crop. The fruit is borne near the base of the shoots of the current season, and the shoots are borne on the wood of the previous year's growth coming from a dormant bud. Here is manifested one of Nature's energy-saving devices, shoot, leaves, flowers and fruit spring in a short season from a single bud. In the light of this fact, pruning should be looked on as a simple problem to be solved mathematically and not as a puzzle to be untangled, as so many regard it. For an example, a problem in pruning is here stated and solved.
A thrifty grape-vine should yield, let us say, fifteen pounds of grapes, a fair average for the mainstay varieties. Each bunch will weigh from a quarter to a half pound. To produce fifteen pounds on a vine, therefore, will require from thirty to sixty bunches. As each shoot will bear two or three bunches, from fifteen to thirty buds must be left on the canes of the preceding year. These buds are selected in pruning on one or more canes distributed on one or two main stems in such manner as the pruner may choose, but usually in accordance with one or another of several well-developed methods of training. Pruning, then, consists in calculating the number of bunches and buds necessary and removing the remainder. In essence pruning is thinning.
An old dictum of viticulture is that the nearer the growing parts of the vine approach the perpendicular, the more vigorous the parts. The terminal buds, as every grape-grower knows, grow very rapidly and probably absorb, unless checked, more than their share of the energy of the vine. This tendency can be checked somewhat by removing the terminal buds, which also helps to keep the plants within manageable limits, but is better controlled by training the canes to horizontal positions. Grape canes are tied horizontally to wires to make the vines more manageable and to reduce their vigor and so induce fruitfulness; they are trained vertically to increase the vigor of the vine.
Winter-pruning of the vineyard may be done at any time from the dropping of the leaves in the autumn to the swelling of the buds in the spring. The sap begins to circulate actively in the grape early in the spring, even to the extremities of the vine, and most grape-growers believe this sap to be a "vital stream" and that, if the vine is pruned during its flow, the plant will bleed to death. The vine, however, is at this season of so dropsical a constitution that the loss of sap is better denominated "weeping" than "bleeding." It is doubtful whether serious injury results from pruning after the sap begins to flow, but it is a safe practice to prune earlier and the work is certainly pleasanter. The vine should not be pruned when the wood is frozen, since at this time the canes are brittle and easily broken in handling. On the other hand, it is well to delay pruning in northern climates until after a heavy freeze in the autumn, to winterkill and wither immature wood so that it can be removed in pruning.
There are three kinds of summer-pruning, the removal of superfluous shoots, heading-in canes to keep the vines in manageable limits and the pruning to induce fruitfulness discussed on a foregoing page, which need not have further consideration. It is very essential that the grower keep these three purposes in mind, especially as there is much dispute as to the necessity of two of these operations.
All agree that the vine usually bears superfluous shoots that should be removed. These are such as spring from small, weak buds or from buds on the arms and trunk of the vine. These shoots are useless, devitalize the vine, and hinder vineyard operations. A good practice is to rub off the buds from which these shoots grow as they are detected, but in most vineyards the vines must be gone over from time to time as the shoots appear. Still another kind of superfluous shoots, which ought to be removed as they appear, are those which grow from the base of the season's shoots, the so-called secondary or axillary shoots. These are usually "broken out" at the time the shoots from weak buds are removed.
While there is doubt as to the value of heading-back the vine in the summer for the sole purpose of inducing fruitfulness, there can be no doubt that it is desirable for the purpose of keeping some varieties within bounds. Heading-back is not now the major operation it once was, the need of severe cutting being obviated by putting the vines farther apart, by training high on three or even four wires and by adopting one of the drooping systems of training. The objections to heading-back in the summer are that it often unduly weakens the vines, that it may induce a growth of laterals which thicken the vines too much, and that it delays the maturing of the wood. These bad effects, however, can be overcome by pruning lightly and doing the work so late in the season that lateral growths will not start. Most vineyardists who keep their plantations up find it necessary to head back more or less, depending on the season and the variety. The work is usually done when the over-luxuriant shoots begin to touch the ground. The shoots are then topped off with a sickle, corn-cutter or similar tool.
There are two ways of renewing the fruiting wood on a grape-vine, by canes and from spurs. The manner of renewing refers to pruning and not to training, for either can be used in any method of training.
Renewal by canes is made each year by taking one or more canes, cut to the desired number of buds, to supply bearing shoots. By this method the most of the bearing wood is removed each year, new canes taking the place of the old. These renewal canes may be taken either from the head of the vine or from the ground, though the latter is little used except where vines must be laid down for winter protection. Canes may be renewed indefinitely, if care is exercised in keeping the stubs short, without enlarging the head from which the canes are taken out of proportion to the size of the trunk. Renewing by canes is a more common method than renewal by spurs, as will be found in the discussion of methods of training.