Rocks:
Although most common, not all trees are grown in pots. There are styles such as ishitsuki that lend themselves to the use of rocks.
Rock or stone cultivation is linked to the origin of bonsai, which originated in China more than 2000 years ago (Penjing) and which attempts to recreate miniature images of nature. The most commonly used rocks are imported from Japan (Ibishi). These are often fused with the tree after years of cultivation. Also very popular are rocks with hollows that fill with water when watering our bonsai trees to form a "lake".