Trust me, as long as the shoots have some roots, they will grow. Canes which tough the ground will almost always root it seems.

They seem to do ok in large pots, ive never tried it myself until this year, but people in here seem to have done it, using a fairly large pot with a double hoop. You just train the canes around the hoop, and cut the tips when they get too long.

From our experience down here, they will live in a 5 gallon pot but didn't produce a lot. Have transplanted 3 of those to old cattle trough (~125 gallon) and they are doing much better. Perhaps a 10-15 gallon pot per plant would be a good compromise.

sounds like some good advice here so far...I recently dug up old bb vines (weak looking and almost dead) and put them in 5 and 15 gal pots. They took off!

Take a look around NW Washington, the himalayan blackberry is incredibly invasive. I live in the Northeast, if you transplanted some around here, I'd be pretty upset as it can have a very drastic effect on the surrounding ecology. My advice is don't spread anywhere where it isn't already established in the environment. It is not the same plant as any old blackberry.

Thornless varieties are larger, taste better, and don't stab you if you eat berries, move them, or cut them back. That's what I do, and I also live in the PNW. They wouldn't survive the winters in the NE.
John S
PDX OR

As an experiment, fine.

Unless your goal is free edible plants only, you would be better off with a named variety planted in the ground.