Q: Do you know what this plant/weed is? If it is a weed, it sure is attractive.

A: I initially thought your was Lady’s Thumb, Polygonum persicaria.

But when I checked with my friend Shannon Pable, she pointed out that your flowers are white, not pink. Her identification is nodding smartweed, Polygonum lapathifolium

Either plant is usually considered a weed because it spreads so readily from stem fragments and from seed. In fact, there are dozens of different polygonum species and they are almost all weed-like. I get equal inquiries each fall on how to cultivate and how to eradicate Mexican bamboo, Polygonum cuspidatum var compacta.

I’ll let you decide what to do about your plant…but I notice in your picture that it has already overwhelmed the juniper nearby.

See
Nodding Smartweed
Lady’s Thumb
Mexican Bamboo