Katamaru is a Japanese term that means hardening a tree. It refers to the process of lignification, which is the transformation of fleshy shoots into woody branches. Katamaru occurs when the new buds and leaves have attained their full growth and stop expanding. Katamaru is related to bonsai trees because it affects the shape and structure of the tree, as well as its ability to respond to pruning and wiring. Bonsai artists need to be aware of the katamaru stage of their trees, as it determines the optimal time and technique for styling and maintenance.