I didn't think it would grow at all since it was in the ground with nothing growing from it in that piece so I tossed it and trash pickup was yesterday...
It's possible it's a pokeweed though. I've read the roots can get over a foot long and 4" thick. There's a newer pokeweed that popped up the last 2-3 years about 10' from where it was, and the big old one behind the garage is maybe 25' away. Maybe at one time it was in more places behind and along the garage, previous owners killed that one off and that's what was left underground.
This is what the really old pokeweed behind the garage looks like right now, the stalks are at 2" diameter from it. I'm surprised there's nothing coming up from it yet. It's a LOT of clean up in the fall to cut it down and I have to catch new ones sprouting up around the yard, but the birds love it so I keep it.
