Moss is a common feature of bonsai trees, as it can enhance their aesthetic appeal and provide some benefits to their health. Moss can help to keep the soil moist, prevent erosion, and create a natural-looking environment for the tree. Moss can also give a sense of age and maturity to a bonsai tree, as it mimics the appearance of trees in nature. However, moss can also pose some dangers to bonsai trees, such as competing for nutrients, harboring pests, and covering the roots. Therefore, moss should be used with care and moderation, and should be trimmed and cleaned regularly. Moss can be collected from various sources, such as rooftops, sidewalks, or tree barks, or it can be cultivated from spores or dried moss. Moss should be planted on a thin layer of organic soil that can retain moisture and nutrients. Moss should also be kept out of direct sunlight, as it can dry out and die.