Roots over A Rock Style (Joju) – When trees grow in rocky terrain, they have to search for soil by using the roots, digging down into the holes and cracks where the best soil is usually found. Since the roots are unprotected and exposed, prior to reaching the ground they have to find a way of finding protection from the sun, which is done as bark grows around them. When growing Bonsai with this style, the roots would grow over a rock that has been added to the pot. Although it might seem like it, training and maintaining this style is actually no harder or different from any other.
Growing in a Bed Style (Ishisuki) – With this style, the tree grows up in between the holes and cracks of a rock, meaning the roots have little room to develop and absorb needed nutrients. In nature, typically trees that grow amongst rocks do not do well, meaning they have to struggle to survive. Therefore, if you choose this style of Bonsai, you will need to be sure to fertilize and water often. Additionally, you would need to place a rock in a shallow dish within the pot, and fill it with water or fine stones.
Raft Style (Ikadabuki) – When a tree cracks, it can sometimes survive by pointing its healthy branches upward, which allows the old root system to provide those branches with enough nutrients to survive and grow. Eventually, new roots will begin to grow out of the side of the broken tree, and then soon consume the function of the old root system. Then, the old branches that are pointing upward will develop because of the higher level of nutrients. The result is what is known as the Raft System. This style is similar to the Yose-Ue and Ikadabuki Styles in that the new trunks emerging are visible from the old, broken trunk.
Driftwood Style (Sharimiki) – Over time, certain trees will become bald or no longer have places of bark on the trunks, generally because of harsh weather. This portion of the trunk will start where the rooms emerge from the ground and then become increasingly thinner, as it travels upward on the trunk. The exposed areas then become bleached by the sun, which now forms a new characteristic on the tree. With Bonsai, a sharp knife is used to remove the bark and as a way of speeding up the bleaching process, calcium sulfate is used.