Buckwheat grains are very hardy. Every year I find a few plants that either didn't germinate when first planted, or fell off some later plant. I do recycle soil I use so sometimes I'll get buckwheat growing in a container with carrots or squash.
I always wait till the seeds are mature and pull up the plant. Buckwheat loves to replenish itself and for every seed I plant, I get lots of seeds per plant even if it's neglected or growing in poor quality soil or in a shady area.
