If you have blackberry vines that are already established in your yard, then you've probably noticed that they have a tendency to spread all over the place. Blackberries -- known by the scientific name Rubus fruticosus -- come in thorny and thornless varieties, and if you get the thorny type, they're not something you want the kids to step on when they're running around bare-footed. To keep your blackberry canes looking tidy and provide them a vertical space to grow, build a simple trellis with some basic tools and equipment.
Dig holes about 3 feet into the ground using a post hole digger, with each hole about 20 feet apart. For the home gardener, two holes will probably be enough, since that will allow you to grow two to four blackberry canes. If you want to grow more than that, dig more holes, spacing each 20 feet from the other.
Place 2 to 3 inches of gravel in the bottom of the hole, and then place an 8-foot wooden post in each hole.
Fill the holes with quick-setting concrete and allow it to dry. While the concrete is drying, hang a plumb line along its length to make sure the post is level. If not, press gently back or forth to make it level and continue to monitor it so that the post does not list to one side. If you're having trouble keeping your posts level, you can nail two 2-by-4-inch boards to the post, about midway up and on opposite sides, allowing one end of the boards to rest on the ground. This acts as a brace to hold the post in place while it dries. Remove the boards after about 24 hours.
Insert a 1/2-inch drill bit into your drill and drill pilot holes into the posts at 5 feet and 3 feet from ground level, on the part of the post that faces the inside of the post -- or in other words, the part of the post that faces the other post.
Twist 1/2-inch eye bolts into the holes, tightening them as much as you can.
Wrap high-tensile wire around one eye bolt, leaving about 1 foot of extra wire at the end. Stretch the wire across the span between two posts, and then wrap the wire around the other eye bolt, again leaving about 1 foot of extra wire at the end. Repeat the process for the second layer of eye bolts, so that in the end you have two spans of wire going across your trellis. To keep the wire in place, wrap the 1-foot extra piece of wire around the tensioned part of the wire.