Ideally, most companion plants should be in a very natural looking container to give a sense of being part of the surrounding environment, rather than being another object to focus on. This depends on the style of the bonsai and its container. In any case there should be a consistency; not necessarily exact—but supportive, in style, texture, and colour. Think of the bonsai, its container, and the companion plant as a large painting, its frame, and accompanying adornments or smaller paintings surrounding it. If there is much contrast in the main display, you want to match that somewhat, at least not further complicate it. If there is not, then at most a minor variation will work. A drastic variation between bonsai and companion in color, shape or texture, or clash of glazed and unglazed, will just take away from the main focus in most cases. As always, there are exceptions, and contrast can add interest to a somewhat drab situation.

Scale/proportion of the planting relative to the bonsai is crucial for a specific bonsai, and the required size of container falls from that. I have seen slightly oversized companions placed somewhat forward of the bonsai, or rarely back, to yield a visual perspective that worked.

The container should either be, or simulate a rock or slab, or have drainage holes and feet, as with any bonsai container. You might get by using tiny flat pots by adding spacers underneath that blend in well enough as feet. Not many typical, but just small, bonsai pots, as we often find locally, work well for companions in our shows, as they just suit larger bonsai than we often have in order to be in correct proportion. Tiny ones and more shallow ones may work. But many wonderful companion plants are composed using natural sections of hollow log or tiny stumps, worked stones (cavities or crevices for soil), or even bark sections.