The Japanese believe it is Important to be harmonious with man and nature. A Bonsai tree is viewed as a work of art. So, the container can enhance or detract from the tree. Ideally, it should compliment the tree. It is important that the tree have a sense of balance in the container to enhance its beauty and symmetry. If all of the elements work together the tree in the container will resemble a work of art. But, there are practical considerations that are first and foremost. The pot size must be able to support the weight of the tree so that it does not fall or tip over. Bonsai trees are generally displayed on mantles or tables so make sure the tree is balanced in the container and is not top heavy, so that it could easily tip over. Consider the overall style of the tree and what container would compliment it. Make sure the container works with the overall flow of the tree. If the tree has been designed to cascade make sure the container will support and allow this so that the tree can dip below the lip of the container.
If you use a pot that is too small, the tree may be at risk for falling over. Bonsai trees are very fragile, so the container that you choose, must be selected with care. Also, consider how much soil you can place in the pot and the size of the tree. You will need to assure that the tree can grow comfortably in a two year span. After two years, you will need to repot the plant and trim the roots. To allow for drainage or spill over, make sure you have a hole in the bottom of the container with a screen. Make sure that the screen holes are large enough to allow drainage and prevent clogging. The tray underneath the container is for over flow. If you under water the tree it could kill it. Make sure the tray fits the container and that it is not too shallow or wide. You may need to drain the tray periodically. It is not a good idea to have the Bonsai soaking in water as that could also kill it. The container may also depend on the type of tree. Fruit and floral trees can tolerate more water so, it is best if the container allows for some over flow of water. The pine and Juniper trees prefer a dry period, so make sure they are not floating in water. So make sure you have enough information to make an educated decision about the type of tree and the best container for it. Some trees live to be 200 years old