Last year I planted my tubers in a raised bed filled with compost and despite carefully sifting through, some small (barely a lump in a bit of root) got missed. They seem to survive winter very well (that bed must have got frozen solid at some point), so like you, I found several new plantlets coming up. Easy enough to lift up though. As they seem to have few pests and diseases (other than slugs), I just replenished the compost and added some manure and have used the bed again for oca - we'll see how this year's tubers fare as to whether a permanent bed is an option.
