Blackberries grown in a home garden will benefit from using a trellis system for support, ease of pruning and harvesting the tasty fruits. Build the trellis prior to planting the blackberries to prevent damaging the fragile root system of the plants. Use a trellis for all types of blackberries, as even the erect varieties will grow and thrive on one. Blackberries grow for many years, so treat any wood posts used with preservatives.
Decide what materials you need. Plan for one heavy post at each end of a planted row 20 to 30 feet wide.
Multiply the number of rows of blackberries you to plan to grow by two. Purchase lighter posts also, if your row of blackberries is wider than 30 feet.
Use a pole digger to create a hole 1 1/2 to 2 feet deep in the middle of the row, at each end. Place the post in the hole.
Fill any gaps around the post using a shovel and the dirt removed. Press firmly on soil to compact soil and secure the post in place.
Use a hammer to staple (or nail) the wire to the top of the end post. Run the wire across to the other end of the row and attach it to the other post. Leave the wires with a little slack to prevent breakage during the winter months.
Attach a second wire 18 to 24 inches below the top wire. Run it across and attach it at the same height on the other post.
Add extra support to the end post through anchoring. Place a stake 2 feet out from the post. Use rope or wire to connect stake to post at an angle.