Fallopia japonica or Japanese Knotweed. Can become a nuisance as it reseeds readily.
I knew someone on this site would be able to tell me. Thanks, ruthiesbees, for the ID! I did some reading about it, and maybe, on second thought, I won't plant any. It's listed as one of the 100 most invasive species by the World Conservation Union. My bees sure do love it, though.
Someone with a lot more bee knowledge than myself once said "invasive species = bee plant".
yup. seems to be the case.