Re-potting is an essential practice for maintaining the health and beauty of bonsai trees. Re-potting involves removing the tree from its pot, pruning its roots, and replacing the old soil with fresh bonsai soil. Re-potting helps to prevent the roots from becoming pot-bound and allows the tree to absorb more nutrients and water. Re-potting should be done in early spring, before the buds start to swell, or in fall, after the leaves have fallen. The frequency of re-potting depends on the species and age of the tree, but generally every two to five years is recommended. Re-potting should be done with care and patience, using proper tools and techniques.