You might want to drill out a few more holes on the bottom of the pot to make sure that it's draining well. If the water isn't coming out of the bottom then you could be drowning the plants. I grow hops both in the ground and in pots with success in N. San Diego County. I can get three or four years of growth in a pot before I'll take it out, divide rhizomes, and start over. Currently, I have three, second-year Chinook plants in pots and they are 20' tall and flowering like mad. They get watered more often (pretty much every day) and require more food then the in-ground ones but do very well. My guess is the roots stopped up your drain holes, so double check that water flows out the bottom when you water and, perhaps, drill a few 1/2" to 1" holes in the bottom of your pots to be sure you have adequate drainage.