Pumice is a natural volcanic rock that is often used as a soil component for bonsai trees. It has a porous structure that allows air to circulate around the roots, while also retaining some moisture. Pumice helps to improve drainage and prevent root rot, which are essential for the health and vigor of bonsai trees. Pumice can be used alone or mixed with other substrates, such as lava rock, perlite, or bark. Pumice is especially suitable for yamadori bonsai, which are collected from the wild and need to recover in a well-aerated soil.