The use of a trellis when growing grape vines is of the utmost importance. Not only does the trellis support the weight of the fruit, but it spreads the grape canopy ensuring sunlight penetrates to all parts of the plant in addition to promoting good air circulation which is essential for keeping down the incidence of diseases which may harm the developing fruit.
Grape trellises can be quite simple depending on the design you go for. You may also consider a decorative option such as training your vines to grow on an arbor or porch. The choice really depends on the variety of grape you are trying to grow and also on personal preference.
Perhaps the simplest of grape trellis designs is what is known as a high cordon system (or high wire cordon system; see Figure 1). This type of trellis can be built with only one wire stretched between posts and the cordons (arms) of the grapevine are trained horizontally along the wire. With this design, you should allow 6 to 8 ft between vines and 7 to 8 ft between rows. This type of trellis is suitable for American varieties and most American-French hybrids as they have a downward growth habit.
Another system suitable for American grapes and hybrids is the Umbrella kniffen system. With this system, there are two wires (upper and lower) stretched between posts. The trunk (or trunks) grow to the uppermost wire and 4+ canes are bent over the wire, while the rest are removed. The tips of the bent canes are tied to the lower wire to create an arrangement that resembles an umbrella (see Figure 1).
If the chosen variety is French then it is likely that the plant will have an upward growth habit and the trellis design will need to reflect this. One of the most commonly used trellises for upwardly growing vines is the Vertical Shoot Position (VSP) system. The VSP system is suitable for smaller varieties and generally consists of between 4 and 6 wires stretched between posts. The cordons are trained to grow along the bottom-most wire which is usually positioned about 3 ft from the ground. The shoots are then trained to grow upwards using the wires above (see Figure 2). It is common to prune the shoot tips to a uniform height and create a hedge-like appearance.
Figure 2. Trellis design for French grape varieties
You may consider a decorative option....
Figure 1. Trellis designs for American grape varieties and hybrids