Sly,
I have some wild blackberries growing around some trees at the back of our property. Two years ago, after all the blackberries were off, I mowed them down with a rotary mower. I was trying to clean up the area. Last year, I got tired of picking blackberries. I made some wine and it came out pretty good so I thought about getting some plants. While reading on line, I saw were blackberries canes last for two seasons. The first year, the canes are referred to as primocanes and do not product berries. The second year, they are production canes which are referred to as floricanes. It turns out the article recommended you cut the canes after fruit bearing to make room for primocane growth during the second half of the spring/summer so basically, I unwittingly did what was recommended. Unfortunately, I did not read the article until late fall so I did not follow the recommendations last year. I plan to relocate some of the root stock since the vines did well in my area and produced good wine. They produced well in the wild so I hope they will do better with care (which has not been my experience with plants). I hope that helps and if anyone else has information, please let me know.
e-wine