Hi, joshaeus.
Water lilies apparently don't need much "soil" to grow in at all. I've planted bulbs in standard 4" clay pots, first lining the bottom of the pot with pea gravel (just a little smaller than the drainage hole in the center) and then a couple of fistfuls of standard potting soil. I push the bulb into the soil just enough to cover it, and then fill the remaining couple of inches with a combination of more pea gravel as well as some pingpong ball sized river rock, to tamp the soil down and prevent it from washing out when submerging the pot. My ponds are 28" deep but I've placed some of the pots on top of 8" concrete half-blocks to make it easier for the lily pads to get to the surface.
This worked really well. When my fish were still small.
What has happened since has turned my ideas on their heads. If you don't have fish, you needn't read any further, but because of my fish, I learned a thing or two more about water lilies.
When my fish got big, they got strong. When I'd feed them, they'd go into a frenzy and charge around the pond, knocking pots over even if they were filled with heavy river rock. They would also plop themselves down right inside the pots and suck out the lily stems as they emerged from their bulbs. I would find the bulbs floating around on the surface with chewed up little lily pad stalks trailing behind them. I'd replant them and the fish would do it (knock them over) all over again. Eventually I got tired of picking up after these fish and left several pots lying on their sides on the bottom.
Then I noticed some pads surfacing in the pond where I hadn't put any pots. I pulled lightly on the pad stems and got strong resistance from the roots somewhere below. Turns out the bulbs had gotten weighted down by the rocks in the planters and then taken to rooting in the large river rocks (hardball-sized) covering the bottom of my concrete pond. Other than the usual half inch of sludge and sand that normally gets into your pond over time, these lily pad bulbs were growing healthy stalks with no pot or soil whatsoever.
Fact is, most water lily species are tougher than hell. I live in central Florida, so I don't have to worry about winter die-off, but I just got back from a trip to the Adirondacks in upstate New York where slow-moving streams were producing wild water lilies at depths from maybe a foot and a half to almost six feet deep.
I guess what I'm saying is that water lilies shouldn't be hard to grow anywhere but in the most extreme climates. They don't require much to thrive and are comfortable at depths from maybe a foot up to the top of your head. Lots of people with acreage ponds consider them to be a weed and a nuisance. Myself, I'm content with the shade and protection from birds that the pads provide along with the occasional flower!
Plus, I've decided to place my pots inside the cores of the concrete blocks so the fish can't knock them over - although they'll still try to pull the sprouts out.
In the photo at upper left are the large lily pads growing from the bottom rocks (28" deep) with no pot at all. The small pads at lower right are a different species growing from the pot lying on its side, bottom right. There are also three cored bricks lying akimbo from fish mayhem. The 12" orange/white koi is the "capo" and all the other koi and comets follow it around.
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