The grape trellis is the support that allows the grape vine to produce a heavy crop. The grape vine itself is soft and not very strong, and it cannot grow upright by itself. A modern vineyard trellis system uses high tensile steel wires with industrial bracing. For the home garden, you can use the same basic vineyard principles and build your own grape trellis that will last through many grape harvests.
A basic grape trellis consists of posts set in a row, with wires strung between them to support the vines. The grape vines are planted at intervals between the posts and trained to grow on the wires.
Design and Build Your Grape Trellis
Assess the contours of your land and plan the distances between vines and between posts. For grape vines that you will space eight feet apart, plan on spacing the posts no more than 24 feet apart in the rows. For a small home garden grape trellis, design the spacing to fit the area you have available.
Decide the kind of post you want to use, wood or metal. Metal posts can cause premature rusting of wires, and in humid conditions they can rust and have a considerably shorter life than wood. Buy the best quality materials you can afford, because the trellis needs to last for 20 or 30 years. Choose the highest grade of treated wood.
Mark the rows with twine and dig post holes, spacing them according to your plan. Set the poles: A two foot depth for a six to eight foot post is typical. Use a level to assure vertical alignment, checking all directions.
Run wires, fastening them to wooden posts with fence staples and to other kinds of posts with appropriate fasteners. Run wires on two levels, the lower wire about two feet from the ground, and the upper wire four to five feet from the ground.
Use Class III high quality wire. Class III has double and triple the life expectancy of the lower classes of wire. It would be a major undertaking to replace a poor quality wire without damaging the vines. (Ref 2, Res 1)
Install wire stretcher bars when you install the support wires. After the wires have stretched and are no longer as taut as you need them, you can easily use the stretcher bars to tighten the loose wires.