i wouldnt go any smaller then a 3 gallon pot, only because if you are growing 1 plant...you would want it to be worth your time, and effort, and get a good yeild. anything smaller in my opinion would just be a waste of time, and lighting. but to answer your question...people have grown decent MJ in shot glasses. the size of your plant has a direct relationship to how much space your roots have to grow in, so the smaller the pot, the smaller the plant.
