i know either the japanese or chinese were experimenting (i think it was with industrial hemp) and they got around a 20' tree or some crap. heard it on the news a few years back.. i would assume though. if you had the right environment etc, i would think it would grow as big as you wanted.. i mean, imagine vegging a pot plant in a garage in a 20 gallon jug or something, spring comes and you have a 10' monster.. now you plant it outdoors, give it another 6 months of sun, love etc.. i could see easily getting a 15+' tall beast.. i am sure the strain, genetics etc would have a heavy factor but with the right strain, you would determine how big it got with your patience..