After looking at lots of pic's I know it's not Fireweed; I'm leaning towards Ludwigia. I had Peruvian Water Primrose (Ludwigia peruviana) sprout behind our deck last year and it grew really tall ... over 6 feet. The plants in the photo's above remind me a lot of that Ludwigia so I'll wait and see.
~ I'm an old gal who still loves playing in the dirt!
~ Playing in the dirt is my therapy ... and I'm in therapy a lot!