A plant growing directly in water is something I've never done. However, since I keep some cattle troughs that catch roof runoff and keep them full to dunk hanging baskets, I've been wanting to try some. I salvaged some packing styrofoam and have used that to make a ring which is holding some juncus. That plant is doing well. Monday a week ago I was in a Lowe's and they had a cart pushed off like they were going to trash the contents. On that cart were sealed cups about the size of a medium large drinking cup that contained water plants. The bottom was clear and the top had a clear plastic bubble so I couldn't really tell whether they were alive or not. I picked up two cups labeled Nymphaea water lilies. I could see live roots in the mesh back at the bottom of one. When I got them home I rigged up a couple of flower pots so they are sitting at the top water level. Within two days of doing that, the one with the roots had leaves at the top of the water line. The other one has growth, but not to the top.

The instructions on the cup say the planting depth is 12-24". I presume that's the depth to plant down in the water? But do they mean from the bottom of the mesh bags or the crown? As they are situated currently the crown is only a couple of inches below the water surface. I have two meter boxes I propose to sink in the trough for containers. I think they will work and that I can anchor the plants in them if I knew how deep I can place those mesh bags containing the plant crowns. Hopefully if I sink the one that already has leaves on the surface, it can still grow and not be smothered.

I looked for a thread with planting advice, but couldn't find one. Is there one in this forum?

I'm doing this post in something of a rush, so it may be incomprehensible. Maybe not.

If they are alive and it sounds like they are, the pot should be submerged at least 12 inches below the water surface and no deeper than about 24 inches. They will reach the surface of the water. Make sure they get 4 to 6 hours of full sun and fertilize them with Pond Tabs about every 3 weeks. They will amaze you with their growth.

Thanks Dave, @TennesseeDave

They have already amazed me with their growth . I wasn't even sure I was buying viable plants and in two days I could see active growth! Depending on which trough I decide to locate them, they may get considerably more than than 4 hours of sun. The cattle troughs themselves are only about 2' deep. They are often called 'knee troughs' for a reason. The meter boxes are about 12". So sinking the one that has growth at the top of the waterline now won't be a problem if I set it at a deeper depth? I didn't expect such rapid growth so quickly.

I'm actually going to move another trough from the barn to the house (they alternate depending on my needs ) and I'll have a lot of leeway on where it's located re sun.

Donald I see no problems placing the plant in deeper water.