What do you plan on doing with the Blackberrys?
I put some thornless blackberry plants in a few years ago and I find that they are almost too sour to eat fresh. They do make an excellent wine though.
It could be the type of Thornless plants that I got too. Mine came from Alaska. They seem to start new growth where ever the canes touch the ground, so in a few years I should have plenty for jelly and wine making.
Last year while fishing I pulled a wild thorned blackberry plant out, put it in a pot for the winter and I plan on setting it this spring. This type is sweet when ripe.