I hear what you're saying, so here's my theory combined with what I've read about the subject on Cannabis roots: They appear to grow to their environment (Sure this is common for all rooted plants.), so having a more shallow, yet wide 'pot' helps the plant grow more wide faster than tall. This lends itself to indoor growing as a 2' to 3' depth pot would steal area for height. It is said a wider plant will produce more colas so the harvest is larger. Also, personal experience example here. I received my first seedling from a friend who had acquired 3. There were 2 marked as the same strain and a 3rd was different, so I chose one of the 2 similar plants. I potted mine into a 20" deep x 20" diameter pot outdoors. (This turned out to be the male I referenced in my OP, so besides learning a bunch, I saved his 2 girls from being seed plants instead of weed plants.) Anyway, he had a plant from about a 6 weeks earlier than these 3, that he put into a 15" x 15" pot. The 2 remaining girls were planted in the ground. Here's what I/we observed. When I pulled the dead male from the pot, it was about 5' tall and about 2' in diameter. The roots were only about 6" deep, but well over a foot in diameter. Friend's potted plant also grew very tall, but only a bit wider than the pot diameter and it's roots were also large diameter, but shallow. In neither case did these grow anywhere near as deep as they could have. The 2 planted in the ground both fell over due to their weight and high winds (Guessing.) Again, while they plants grew large and bushy but not very tall, their roots were wide, but shallow. Too shallow to support their heft once they went to flower it seems. Anyway, that's what I know. FYI, the strains were aptly named 'I fell over and I fell over 2'. I wonder if the strain has any bearing on the root structure. I'm also speculating that those farmers are growing Hemp, not true Cannabis (For a number of reasons, obviously.), which is actually a different, but similar plant? I remember the first time in rural Illinois farmland and stumbling across a huge crop of Hemp, not knowing that's what it was. I thought I'd stumbled on a goldmine, only to be told 'It ain't that kind of weed, LOL!'