I used 1 gal pots that are 6 1/2" deep (I actually just went and measured them) and they where not filled to the very top but they had a good 5 to 6" of soil in them. That doesn't mean you have to, but you can see (post 419) that even with mine the roots started to circle and the like. But I started mine in standing water as well. I just figure more soil means less likely to dry out, without having to dig huge holes later. This year will be my first attempt in trying to grow a few directly put into soil. I think shallow soil is fine as long as you can keep damp enough to get roots to form and stay damp enough to encourage growth, but not too wet to stunt growth. As I understand MG once rooted doesn't like standing water or real wet feet.