Buckwheat has been grown in places where other plants won't grow for centuries. Peasant folk who live in the mountains will toss handfuls of buckwheat groats up onto rocky hillsides, because the grain will fall into bits of soil which have accumulated in crevices and buckwheat plants will sprout up.
Because I transport garden soil from one place to another, I get buckwheat "volunteers" in all kinds of interesting places, from seed which dropped off the plant onto the ground. When the dirt got moved, so did the seeds.
I was pulling weeds in the side yard recently, and discovered two different buckwheat plants growing where the driveway has cracked apart and soil has settled in. One was right in the driveway and one was along the edge, where some weeds had also found a home.
I love to find these plants, which even when small can have 20 seeds on them. One seed multiplied to twenty is a good return, especially since they aren't plants I ever did anything to establish!