I ordered some pickerel rush once from Lilypons, and they said to
plant it in heavy soil, and then put 2 inches of gravel on top, to keep the dirt from getting in the water. I guess just don't use dirt with peat or compost in it, or any of those little white styrofoam-looking things.
They sell plain old plastic pots with no holes in the bottom, but a book I have from the library says its just as good to
plant in a plastic bucket and cheaper. That book said the dirt isn't all that vital, just something to hold the
plant down, because the
plants get most of their nutrients from the water and from fertilizer you give it.
I ain't no expert, but hope this helps!