These two pictures show vastly different approaches to growing blackberries.
First, in a well-tended home garden (so, obviously one belonging to neighbor!):
The gardener installed two metal stakes, about four feet above ground, with chicken wire running vertically the length between them to make a fence. Blackberry canes are grown in two rows, one on each side of the chicken wire fence. The canes are further supported by thick, insulated cording (here, the turquoise cords) running horizontally the length of the fence. The cords are spaced a foot apart. The tops of the canes are unfettered; they bend down gracefully with the growing fruit. This framework allows easy harvest from both sides of the structure.
Second, wild in the Pacific Northwest:
Blackberries cost a pretty penny in my part of the world, so I never believed my friend's assessment that these plants are weeds in her home town in Washington. Then I took a trip to Oregon and saw for myself. Not only were blackberries growing along the road and in every ditch, I also saw them growing in rocks at a pier. The cords here are not a trellis at all -- they're to keep people from falling in the ocean! I bet the locals are sick of blackberries.
Just goes to show that weeds are all a matter of perspective. What "weeds" are your favorite?