hey- my friend grows northern light plants, and gets anywhere from a half of a lbs, to a whole lbs from them using 5 gallon buckets. do not worry about it, just dont vegg them above 5 feet in the buckets, most root growth occurs durring vegg, meaning, if your not root bound by the time u flower, u wont be. he has had some get root bound, but only when he vegges them to 6 and 8 feet, trying to get a 12-14 foot plant, but, flower at 5 feet, you willl get an eight footer, and probably 3/4 of a lbs, transplanting is too risky after 3feet, he also made a "sandbox, about 3 foot wide and 10 feet long, about 1 foot deep, and he drill 1.5 inch wholes in each pail, at the bottom, maybe 9 holes in each pale, he then burries them half way in the "sand box" he made, sometimes, the larger plants, will actuaally root thru the wholes and grow thru the homeade sand box, consider drilling your holes carefull before their 4 foot tall, you should have an awsome grow, he says if you have sativa, a good strain, and u do this, u can get 5 lbs of 7 plants, everytime. good luck