Different climate, and I've only been growing hops for a year, but here in NC I've got twenty or thirty plants in the 14" clay pots they sell at the hardware store. I only planted one rhizome in each pot, but for the first year at least they seemed happy enough - the vines all got about 18' tall and most of them set cones. I was very diligent about watering, fertilizing, and keeping the pests off of them, so that may have been a factor. I expect I'll have to transplant most of them this year, or un-pot them and prune the roots or something (assuming they overwintered OK)