It is impossible, therefore, to state for any particular variety or any particular location the best style of pruning to be adopted. All that can be done is to give the general characteristics of the variety and to indicate how these may be modified by grafting, soil or climatic or other conditions.
The most important characteristic of the variety in making a choice of a pruning system is whether it normally or usually requires short, half-long, or long pruning. With this idea, the principal grapes grown in California, together with all those grown at the Experiment Station on which data exist, have been divided into five groups in the following list:
- 1. Varieties which require long pruning under all conditions.—Clairette blanche, Corinth white and black, Seedless Sultana, Sultanina white (Thompson's Seedless) and rose.
- 2. Varieties which usually require long pruning.—Bastardo, Boal de Madeira, Chardonay, Chauché gris and noir, Colombar, Crabbe's Black Burgundy, Durif, Gamais, Kleinberger, Luglienga, Marsanne, Marzemino, Merlot, Meunier, Muscadelle de Bordelais, Nebbiolo, Pagadebito, Peverella, Pinots, Rieslings, Robin noir, Ruländer, Sauvignon blanc, Semillon, Serine, Petite Sirah, Slancamenca, Steinschiller, Tinta Cao, Tinta Madeira, Trousseau, Verdelho, Petit Verdot, Wälcherisling.
- 3. Varieties which usually require short pruning.—Aleatico, Aligoté, Aspiran, Bakator, Bouschets, Blaue Elbe, Beba, Bonarda, Barbarossa, Catarattu, Charbono, Chasselas, Freisa, Frontignan, Furmint, Grand noir, Grosseblaue, Green Hungarian, Malmsey, Mantuo, Monica, Mission, Moscatello fino, Mourisco branco, Mourisco preto, Negro amaro, Palomino, Pedro Zumbon, Perruno, Pizzutello di Roma, Black Prince, West's White Prolific, Quagliano, Rodites, Rozaki, Tinta Amarella, Vernaccia bianca, Vernaccia Sarda.
- 4. Varieties which require short pruning under all conditions.—Aramon, Burger, Chardonay, Chauché gris and noir, Colombar, Crabbe's Black Burgundy, Durif, Black Morocco, Mourastel, Muscat of Alexander, Napoleon, Picpoule blanc and noir, Flame Tokay, Ugni blanc, Verdal, Zinfandel.
- 5. Varieties of table grapes which usually require half-long or cordon pruning.—Almeria (Ohanez), Bellino, Bermestia bianca and violacea, Cipro nero, Dattier de Beirut, Cornichon, Emperor, Black Ferrara, Malaga, Olivette de Cadenet, Pis-de-Chevre blanc, Schiradzouli, Zabalkanski.
These lists must not be taken as indicating absolutely for all cases how these varieties are to be pruned. They simply indicate their natural tendencies. Certain methods and conditions tend to make vines more fruitful. Where these occur, shorter pruning than is indicated may be advisable. On the other hand, other methods and conditions tend to make the vines vigorous at the expense of fruitfulness. Where these occur, longer pruning may be advisable.
The more usual factors which tend towards fruitfulness are:
- Grafting on resistant vines, especially on certain varieties such as those of Riparia and Berlandieri;
- Old age of the vines;
- Mechanical or other injuries to any part of the vine;
- Large development of the trunk, as in the cordon systems.
The more usual factors which tend towards vigor at the expense of fruitfulness are:
- Rich soil, especially large amounts of humus and nitrogen;
- Youth of the vines;
- Excessive irrigation or rainfall (within limits).
In deciding what system of pruning to adopt, all these factors, together with the nature of the vine and the uses to which the fruit is to be put, must be considered. It is best when the vineyard is started to err on the side of short pruning. While this may diminish slightly the first one or two crops, the vines will gain in vigor and the loss will be made up in subsequent crops. If the style of pruning adopted results in excessive vigor of the vines, it should be gradually changed in the direction of longer pruning with the object of utilizing this vigor in the production of crop.
This change should be gradual, or the risk is run of injuring the vitality of the vines by one or two excessively heavy crops. Finally, each year the condition of the individual vine should determine the kind of pruning to be adopted. If the vine appears weak, from whatever cause, it should be pruned shorter or given less spurs or fruit canes than the year before. On the contrary, if it appears unnecessarily vigorous, more or longer spurs or fruit canes should be left. Every vine should be judged by itself. It is not possible to give more than general directions for the pruning of the whole vineyard. It cannot be well pruned unless the men who do the actual pruning are capable of using sufficient judgment to properly modify their methods for each individual vine.