@thehardygardener I planted it in very fine sand that was lying in a pile by the fence. It may be river sand. I rinsed it pretty thoroughly before setting the plant on it. To keep the plant from floating away, a layer of lava rocks was placed on it. Finally, a top dressing of aquarium substrate was added to hide the lava rocks. The container is sitting in my pond, at least two- thirds submerged.