thin landscapre fabric allows the roots to grow through. I have roots in the bottom of my two earth boxes that have grown through the fabric. The roots grow through my net cups also in my rain gutter grow system. I line my net cups with the same fabric.

I pack a layer of moist soil down first. I don't want to impede the openings, because my tomato plants roots all end up in the water reservoir. I get some dirt on the bottom, but it's easy to clean.