The main issue would be the top soil fouling your pond water. Our soil sucks, rocks some clay, potting soil you should never use, it floats.
I used clay, the friend that sent me the tubers said that is how she planted hers, and searches on the net said the same. I put 1/4 cup of osmocote in the bottom of the pan, filled with the cheap wally world kitty litter, pure clay, stuck the tuber in and put in pond. I have not had lilies before so it was guess work for me.
Now I just wade out into the pond, clip off old leaves, old flowers, and stick in a plant tab off and on. The group of pink ones towards the center of the pond I got off of craigs list last year, right at fall, those overwintered then started growing this spring. All other ones were new tubers this year.
Most of them small starts.
The liles cover half the pond, I could push the pink ones deeper, but they would be hard to keep groomed........I would need my snorkel gear.
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