Hops in Planter Boxes

[realfutbol6]

I have a 3 year old Pacific Gem, a 1 year old Columbus, and a 1 year old Zenith plants that I need to move to tall planter boxes for the season (my large dog has killed the other 2 plants by continuously peeing on them). How big do the boxes need to be to not impede growth? is 2'L x 2'W x 3'H with an open bottom big enough?

 

[Vellum]

Mine are in 2'L x 2'W x 1'H with an open bottom and are plenty big. Hops are happy and healthy. I have some pictures up on instagram @createjake

 

[brewcat]

Boxes will always impede hop growth.