Trellised vines in the winter. The two cordon arms of the vine can be seen running along the cordon wire.
The grapevine is a runner-plant, and a trellising system should be used in order to obtain maximum production of the vineyard or to produce a high quality product. This will in turn ease cultivation of the vineyard. The benefits of trellising include better light intensity in the vines and improved bud fertility. This leads to an increase of the leaf surface and facilitates cultivation practices. Optimal use of sunlight is important and the larger the leaf surface, the greater the process of photosynthesis. A north-south row orientation is a better use of sunlight, but it may run the risk of sun damage in warmer areas.
Various trellis systems are currently being used in the industry. In wine farming the following four systems are used: pergola, hedge, mechanical and alternative systems. Trellis systems for table grapes are usually higher because it requires a lot of manual labour and therefore must accommodate the movement of workers under the plant.
The wine target also determines the size of the trellis system. For example: medium to smaller systems for high quality and low yield in a cool climate versus larger systems for mass or bulk wine production in a warmer climate. The most common mistake that is made is to set up too small and cheap trellis systems that can not accommodate the growth force.
Establishing a Trellis System
After the soil preparation and planting of the vines, it is possible to start the construction of the trellis system. The ideal is to first plant the posts and then the vines. Wooden posts and wire are not always freely available and must be ordered in advance. In South Africa, pressure treated wooden posts are mainly used for the trellising, but nowadays there is a tendency to move away from this practice. Some producers have already begun to use concrete, plastic or iron posts.
The anchor holes are first marked out after which the anchors are fastened and then the anchor posts. Where strong winds occur, posts must be planted deeper. The primary purpose of the anchor is to anchor the trellis and prevent the posts from capsizing and the wires from being flimsy. An anchor can be a concrete block or a steel pole in rocky soil. After all the holes have been dug for the posts, posts can be planted. The outer row would be planted first and thereafter the middle row’s posts in each row. The anchor post is used on the end of the row and is usually planted at an outside angle.
The trellis posts should be planted between 45 and 60 cm deep and the post spacing should preferably not exceed 7 meters. In order to practice good canopy management later, a canopy strand (wire) is used so that the leaves and shoots are exposed to the sun. The canopy strand is fastened with a wire stuck through a small hole in the post or with a staple and should not be pulled tight until the anchors are fastened properly. The steel wire should preferably be tightened in the afternoon or only when it is hot. This will prevent the wires from slipping when it gets hot. Cordon and canopy wires are tucked between the trellis posts. The vines and shoots are tied to these wires to expose the grape bunches to air and sunlight.