For smaller or more delicate root balls, I knead off of as much of it as I can with my hands. I've found that the root balls of landscape plants tend to be more tight so the soil can be hard to get off. I've used the flat side of a shovel or trowel to try. In some cases, I was only able to get the top layer of soil off. This little Dracaena Lemon Twist in a 4" pot is really growing. A large root is already coming out the bottom. I'm going to plant it into a  low ceramic bowl with a couple of other dracaenas.