use 10-20 gallon pots to get really big plants i have done both in ground and bucket.
the bigger the bucket the bigger the root system the bigger the plant. in theory but i have definately seen a difference with big pots vs little pots.

if you do plant in the ground make sure you ammend the soil. i've had plants yield
1/4 lb in the ground and not too far off from that if in really big pots.