There are several main objectives when anchoring a bonsai tree to its container.
The first is to stabilize the tree so that the roots do not move. Roots, especially tender feeder roots, are fragile and easily broken. A tree that is allow to move, even slightly, in the wind or when relocating on a bench, will not establish a proper root ball and over time this will affect the health of your tree.
Another reason for making sure the tree is stable in the pot is that a strong wind can tip the tree out of the pot. Most bonsai pots are quite shallow. If your tree is not wired into the pot, especially if it is a slant, semi-cascade, windswept, or cascade style, it can easily fall out of pot and be damaged.
The second objective when anchoring a tree to the pot is making the attachment as close to invisible from the outside as possible. We want the presentation of our trees to be free of any visual intervention. Any wires, chopsticks, or supports should be hidden under the soil line.
We use wire to anchor trees to their pot. Since the tree will be in this pot, in most cases, for at least two years, we want to use wire that does not stretch over time. That means the aluminum wire we use to move branches is not a good choice for anchoring. Copper is better but can be quite expensive for this purpose.
The best solution is galvanized steel fencing wire. It is very strong, does not stretch, and economical. A gauge between 16 and 19 works well for bonsai applications. You can find fence wire at outdoor or feed stores, and some hardware stores. It is generally not available at the big box stores.
The Virginia Bonsai Society has regular monthly workshops where you can learn more about proper anchoring of your trees into a pot. These are open to all members. You will find a schedule of our workshops in the calendar page on this website.