Name: Jeanie Minnesota (Zone 4a) Replace your lawn with a garden!
That's exactly where I was going with my questions. If this is Japanese knotweed, you cannot get it out of your yard fast enough...and dig down deep and sift the soil where it was, and keep a very close watch on it for about the next 10 years. The zig-zag stems and alternate leaves are what tipped me off. It is probably the most invasive plant on earth. I have been battling it for over 20 years in my yard. I did not know what it was at first and I also thought it was nice looking, but don't make the mistake I did and leave it there. Here are some pictures:
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Old gardeners never die. They are just pruned and repotted.