How to Build Blackberry Vine Supports

Dig two 24- to 30-inch-deep holes with a post-hole digger. Each hole is for the support posts for the trellis system that will stretch over the row of blackberry plants. Position the post holes 30 inches away from both end plants in the row. As you dig the holes, angle the hole 5 to 10 degrees away from the row ends. This results in posts that lean slightly away from the plants in side profile.

Cut an 8-foot-long 2x4 piece of wood with a cross-cut saw or circular saw into two identical pieces 42 inches long. Use a tape measure to ensure pieces are the same length, making a mark with a pencil or scratch so you know where to cut. Also make a mark in the center of each 42-inch-long piece -- at 21 inches -- so you know where to attach it to the posts.

Press both pieces of 42-inch-long 2x4s together, wide side together, and set them so one of their 2-inch wide sides faces upward on the ground. Measure in 3 inches from both ends on both 2x4s and make a mark. Drive a 4-inch-long nail halfway into the top of the 2x4s at each of the four marks. These exposed nails help secure the cross-wires in the trellis system later.

Lay the 6-foot-long 4x4 posts on the ground so they are stable. Measure down from the top end of the post and make a mark at 6 inches. Place the wide side of a 42-inch piece of 2x4 against the post so it's 6 inches from the post top, with the exposed nails on the cross beams facing upward. Drive three or four 4-inch long galvanized nails into the center of 2x4, attaching it strongly to the 4x4 post. Do the same on the second post and 2x4 piece. You now have two crosslike structural braces.

Place a cross brace post in each of the pre-dug holes. Orient each post so the attached 2x4 cross brace faces outward, away from the row of blackberries. Backfill the soil into the holes, tamping it down with the pole end on the shovel. Make sure the posts still angle 5 to 10 degrees away from the blackberry row once the holes are filled and securely tamped down.

Measure the distance between the two posts with a tape measure. Add 4 feet of length to that measurement. This is the length of 9- or 12-gauge wire length needed to create the trellis in between the posts. Cut two lengths of wire, one to use on each side of the cross-beams on the posts.

Wrap a wire end, with 24-inch-long overlap, around the 2x4 and exposed nail on both arms of the cross-beams on a post. Twist the wire around itself and at least once around the nail to stabilize it. Twist the wire until all 24 inches of wire overlap is neatly spiraled and attached onto itself.

Gently pull and lift each wire to then attach it to the exposed nail and cross-beam on the post on the other side of the blackberry row. Another person can assist with stabilizing the post and cross-beam as you lift and twist the wire, creating a taut trellis that measures about 3 feet above the ground.

Lift any stems -- called canes -- of the blackberry plants upward in between the two taut wires. Let the canes flop down onto the wires. Train any new, elongated branches to remain within the two wires in the wire support trellis.