Plant them so they're laying the long way or horizontally and no more than a few inches deep. I think they don't like being too deep and won't come up if they are! Mine didn't even have rhizomes when I got it as a tiny cutting and I just repotted the whole plant, but later it developed large rhizomes , which dont' seem to come up if they're the ones , which have hit the sides of the pot and grown to the bottom. Once they're removed however and planted shallower , they then grow fine. If you see some enlarged areas with a point showing on the rhizomes, those would be the eyes for future stems and shoots and should be planted so they're pointed upward and just with a few inches of soil as previously mentioned. They look a bit like canna rhizomes if you're familiar with the "eyes" on those.