Building a trellis for vines to grow on can use a simplified variation of post-and-beam construction. The 'posts' are the vertical supports for the trellis; make sure to use treated wood or cedar so they will hold up as they are exposed to the elements. The 'beams' are the horizontal support in the trellis construction which will hold the vines. A two- or three-wire trellis system is necessary when you are growing plants such as blackberries, grapes and raspberries.
Measure the length of the planted row or area where you intend to plant the vines.
Dig a 4-inch square by 20-inch deep hole at each end of the row. Line the base of each hole with a 2-inch thick layer of gravel.
Stand a 4-by-4 treated wood post measuring 9 feet long into the center of each hole. Backfill the soil around the post, if necessary, to make sure that the posts are held securely.
Measure and mark the ground between the two posts in 20-foot increments. Dig 2-inch square by 20-inch deep holes at each mark.
Add 2-inches of gravel to the base of each hole. Stand 2-by-2 treated wood posts that are 9 feet long into each hole. Fill around the posts securely with soil.
Mark each vertical support post 6 feet, 4 feet and 2 feet from the ground with a marker.
Unroll 4 feet of 12-gauge wire but do not cut it from the spool. Tightly wrap the wire securely around one end post at the 2-foot mark. Unroll and stretch the wire to the next support post, 20 feet down the row. Wrap the wire tightly around the post at the 2-foot mark. Continue stretching the wire and wrapping it securely around each post at the 2-foot mark along the row. Cut the wire from the spool after wrapping the end post.
Repeat Step 7, but wrap the wire around the 4-foot mark of each post on the row. Then, repeat at the 6-foot mark of each post on the row.