I forget where I saw it, but somehwhere on the web someone did a huge outdoor grow and dug a huge plot 20X40 or something like that and then let it sit for a year or something, I may be way off base but all I know is the plants were monsters...like fdd2blk, 04ausername, and hodge grow. these things were Trees not plants...anyway point I was trying to make is the farther those roots can travel the more growth you will have. The huge plot allowed the roots unlimited growth area. Big plants need lots of roots to move lots of H20 and nutes to create new cells. I am no expert, but I bet you ask any of the guys growing 10ft+ plants on the regular and they will tell you root mass is major factor. Hope this helps, if anyone knows the grow I am talking about please fill in... just finished