Doing bonsai many times is an attempt to mimic nature. In doing so, the bonsai artist, many times will use rocks, water elements, moss, and clay figurines such as people (mud people). These would be found in the category of bonsai
supplies. And can be categorized as a bonsai art, but sometimes refered to more specifically as penjing.
Rocks
Rocks come into play with bonsai trees in two main ways. One, they are used with the tree. Rocks are many times combined with trees, water elements, moss, and clay figurines such as people (mud people), animals, bridges, houses, etc. Rocks primarily represent to image of mountains. Using different materials will bring about different resulting styles. And two, they are often alone in substitute of a tree. Associated with the art of bonsai, are Chinese Rock Plantings. Using rocks, the artist attempts to imitate nature, the way we try to do with bonsai forests.
Water
Using water with your bonsai creations may sometimes require special accessories such as water containers, or special designed bonsai pots that hold water. Using water and gravel makes for a beautiful carved river, or having a small pump may even give you a small waterfall.
Moss
Moss is commonly used with bonsai. Moss is sustained by keeping a shady and humid environment. This environment often appears around the base of a tree in real-life, as the canopy creates shade. Therefore, even if your tree requires a lot of sun, the shady area under the canopy of your bonsai tree is where moss should thrive. Having a humidity tray will help even more.
Figurines & Decorations
A variety of different decorations and bonsai figurines are available for the bonsai hobbyist. They come in different sizes, categories, and materials; however, most of them are made of clay. The clay figurines that resemble people are often called bonsai mud-men. The basic rule to stick to here is to make sure the size is in proportion with the surrounding elements, such as your trees and mountains. Other categories of figurines are animals, and man-made structures such as houses and bridges.