Vermiculite is a mineral that can absorb and retain water, as well as provide nutrients to plants. It is often used in gardening as a soilless growing medium, mixed with other components such as peat moss or perlite. Vermiculite can be beneficial for some bonsai plants that need more moisture and have high pH levels, such as ferns, bamboo, and cacti. However, vermiculite alone is not enough to support the growth and health of bonsai plants, as it has poor aeration and can cause root rot. Therefore, vermiculite should be used sparingly and in combination with other materials that can improve drainage and oxygen supply to the roots of bonsai plants.