The biggest plant I've ever seen was in some pics from this guy who grew a plant in a field near his home. He posted about it on overgrow.com a year or two ago, when that site was still around. What happened was, it got huge, and he couldn't bear to kill it. So he built a structure around it and kept it alive through the winter, ran electricity there and kept it heated and lit, and it ultimately ended up more than 16 feet tall, a virtual tree. He got busted eventually because of this suspiciously odd-looking two-story structure sitting in a field with the tree in it. A crying shame he didn't get to harvest it.