Construction of a trellis for growing fruit is similar to construction of a fence, according to Oregon State University. So it should come as no surprise that you can erect a trellis along fence rows and grow fruit within these rows. Most fruits-like grape vines-grow on a single wire or double wire trellis. When constructing a trellis in a fence row, you must take care to make the trellis sturdy enough to support the fruit without collapsing.
Hammer wooden stakes into the ground at each end of the fence row. Attach a piece of string between the stakes to mark the row and guide your post holes. Your trellis may be of any length provided it is properly constructed.
Dig holes for your line posts along the fence row. The line posts will hold the trellis off the ground and support the weight of the plants. Each hole should be 2 feet deep and spaced 21 feet apart.
Dig the holes for your trellis end posts that are 4 feet deep and slanted away from the trellis at a 45 degree angle.
Fill the bottom third of each hole with gravel. Set the posts into place in each hole.
Mix concrete mix in a bucket with water until the mix is the consistency of cake batter. Pour the concrete into the holes around the posts and allow it to harden.
Stretch wire between the posts along the very top of each post. Insert a tightening device into the wire at one end of the trellis. You will use the tightening device to take up slack in the wire whenever it sags. Attach the wire at each end by wrapping the wire twice around the end post. Then twist the loose wire end around the tight wire end twice while running the loose wire end back along the trellis to the next line post in the trellis line.
Tack the wire to the line posts by hammering a fencing staple into the post around the wire. Leave the staple loose enough that the wire can move freely through it.
Attach a second wire at a point 3 feet up from the ground for a two wire trellis system.