I don't think you can leave it in a one gallon container short of possibly removing it, trimming the roots and then repotting it. I would find a pot equiv to a two gallon and use that. You may be able to keep it in that size indefinitely as long as you regularly pull it out, trim the roots and repot it with fresh mix. Regularly being once every year or two years max. I'd be opting for a three gallon size, personally, with the same routine of repotting.

Suz