The DIY Network recommends sinking two 8-inch pressure-treated 4x4 posts 3 inches deep in the ground to create the trellis' posts. However, people working in sandy soil may add a quick-setting mortar mix to anchor the posts. People working with clay soil may tamp down the soil to hold the posts in place.
The DIY Network also recommends setting these posts anywhere from 10 inches to 20 inches apart. The builder must then make one mark at 2 1/2 inches off the ground and another mark at 4 1/2 inches off the ground to attach a 9-gauge coated wire to the posts with staples. The site then explains that the first year of growth does not require training for the blackberries to grow on the trellis. However, during the second year, the canes must be tied to the trellis. The builder may achieve this by loosely tying primocanes to the wire as they develop, usually before the buds swell in early spring. The builder must then tie the canes horizontally along the top wire when the canes grow tall enough to reach it. The DIY Network also mentions that some gardeners use this method to train only the floricanes to the trellis and let the primocanes sprawl on the ground.