Grapevines can be supported and trained to a variety of structures. In the home garden, structures range from the decorative arbor to the conventional trellis.
Construction of a grape trellis is similar to constructing a farm fence. The trellis must be substantial enough to carry the weight of the vines plus a heavy crop during high winds. Basically, the trellis consists of two or three wires, one above the other, stretched tightly and secured to firmly-set posts.
End posts serve as the anchor points as well as wire supports. End posts are generally 8 feet long, with a diameter of 4 inches, set approximately 2 feet deep in the soil. They may be braced in several ways. A common method is to set an extra post within a few feet of the end post. A heavy piece of wood or another post makes a good brace between the two end posts. Line posts are also about 8 feet long, but with a diameter of 3 inches. They are set approximately 2 feet into the ground and spaced about 24 feet apart within the row.
Use galvanized wire for the grape trellis. Galvanized wire is durable and does not cause serious wire chafing of young vines. Wire sizes commonly used include numbers 9, 10, or 11. Wires are secured to end posts in various ways. A common method is to wind the wire around the post once or twice and then twist the end several times around the wire as it is stretched to the next post. Some gardeners use special devices to attach the wires to the end posts because they simplify tightening of the wires. These devices employ cranks that eliminate removing the wires from the end posts when tightening. Wires are fastened to the line posts with ordinary staples. Space the wires vertically according to the training system to be followed. For example, a 4-cane-Kniffin system would use 2 wires. One wire should be 3 feet above the ground and the second wire 6 feet off the ground. The 6-cane-Kniffin system uses 3 wires positioned 2, 4, and 6 feet above the ground.
The best time to construct a grape trellis is during the first growing season. Tying new shoots to the trellis wires allows for straight grapevine trunk development in future years.