Whether you grow grapes in a large vineyard or in your own backyard, you are going to need some sort of grape trellis to support the plants so that the fruit is above the ground. Not only is an established grapevine that is laden with bunches of grapes quite weighty, but you also need to train the plants to form a framework that will enable you to both grow and harvest your crop with ease.
In general terms a trellis suitable for growing grapes will either be functional or it will be decorative as well as functional.
Functional Grape Trellises
The basic type of functional trellis for growing grapes is the type you will find in vineyards all over the world. These are made from some sort of upright posts or poles and suitable wire that links the uprights together. Usually the trellis will have two rows of wire, one a bit more than three foot (or a meter) above the ground and another about 12 to 16 inches (or 300 to 400 mm) above the first one. The bottom wire is used to branch the main stem laterally, while the top wire supports new growth. The wire should be galvanized so that it doesn't rust when it gets wet over time. Make sure is it suitable for a trellis.
Posts for a basic trellis are commonly made of wood - either wooden pressure-treated posts or a hardwood that is rot-resistant. Other suitable materials include metal (iron, aluminum or even stainless steel, although this is comparatively expensive) or PVC.
Whatever material the posts are made from, you will need to drill holes for the wire to go through them. Clearly it is simpler if you do this before assembling the trellis otherwise you will need a cordless drill to work in the 'field'.
Make sure the holes are the right size and neither too big, nor too small, because the wire needs to be stretched taut. Also make sure the posts or poles are long enough for you to bury in the ground. If you don't concrete them into the ground, they will need to be longer to avoid being affected by the wind. If you aren't going to concrete the posts, it is usually best to use an auger to dig the holes so you don't disturb too much soil - otherwise you'll have to spend more time compacting around them.
Decorative Grape Trellises
The simplest decorative trellis could be described as an old-fashioned arbor, and really all it is a functional trellis with a beam across the top. Of course you could also make the trellis by attaching laths positioned both horizontally and vertically, which is how a true trellis is constructed. But you need to have supports for the grapevines, so these aren't really that practical.
Many of the ready-made grape-trellis designs are also more decorative than practical, so it's best that you learn a bit about planting, growing and pruning grapes before you buy one off-the-shelf. There's no point in having a trellis that look beautiful if it isn't going to fulfill the function for which it was bought, namely supporting your grape crop.
In home gardens and even some backyard vineyards, grapes are often grown on pergola-type structures so that they cover a paved area. It's a double-deal because you get shade and a fruit-crop as well. Again, you need to know how to accommodate the growing vine so that it can be trained correctly. Grape vines are not the same as other creepers and climbers, and you need to understand how they grow. For example, grapes don't grow from old wood but are rather produced from new shoots every year. This means you need to prune the old growth in the correct way to encourage fruiting.
A common fault when growing grapevines over pergolas is to allow the plants to develop branches at different levels. While this approach will probably give you more leaf cover, the top branches will rob the lower ones of nutrition, and the lower ones might not produce grapes at all.
A good way around this is to plant a couple of vines to cover the sides of the structure and then a couple more to produce a living ceiling. The vines on the sides then produce grapes at one level, and those on top will flourish on their own.
