What is that?

Teagan and I spent some time in the yard. We were weeding and planting. Well, I was weeding. Teagan was pulling up my sedum. We planted this meadow sage along our back fence. It was home to a couple tomato plants and a cucumber last year, but has been empty up until today. This is the opposite side of the fence. I think I planted 2 coneflowers, 2 coreopsis, 2 achillea, and 2 of something else two summers ago. It's starting to look a little chaotic now.
Anyway, the question of the day is, what the heck is this? I have been concentrating on weeding the actual garden. Since this has been growing back by the compost bin, I have just ignored. Don't let the picture deceive you. Whatever it is, it is about 5 feet tall with a stalk as thick as a tree branch. Any ideas? Behind it, you can just barely make out the pumpkin plant that appears to be growing in last years compost heap. So much for throwing out the jack o lanterns.
Here is a close up of the flowering part. While I was back there, trying to figure out what this is, Teagan was standing on the back step, yelling at me to come make him a drink. Apparently, I was taking too long. He attempted to come get me but tumbled off the last step instead.