Grow bags are made of breathable fabric which means superior drainage and aeration. It is the aeration that makes them superior to other garden containers. If a container has no aeration and the roots reach the walls of the container, they give a signal to the plant to make more roots, resulting in a root bound plant. Eventually the plant just kills itself with a mass of roots going round and round in the container. .

Root bounding will not happen in a grow bag. Here if a root reaches the wall of the bag, it will be “burned” off, causing the plant to constantly produce new and healthy branching roots. This is also called air-pruning. This picture shows nicely how the roots did reach the wall of the bag, but did not go round at all.