I planted them with the roots over a sponge and within a monthe their center stocks turned brown. They had indirect sunlight and fish waste in the water column for fertilizer.
This is the best way that I have tried for planting peace lilies. This one is potted up in a riparium planter filled most of the way with hydroton, and then with a thinner layer of clay gravel on top.
Once they get going peace lilies generally grow real well in a riparium. They are one of the easiest plants for ripariums.