Reply to a question place on another category of this forum:
The prescribed way to plant lilies is to put them in a mix with 60% normal garden soil with a bit of clay, 20 % sand and 20% potting soil, and cover the top with gravel.
However, I found that the potting soil, if it is too rich, tends to create algae blooms, and the sand tends to mess in the pond. Therefore, I mix gravel and normal garden soil with clay and stick a fertilising stick into the pot from time to time, covered with course gravel and they are very happy.
You always have to start with a small pot and as it grows bigger, increase the pot size. They tend to die if the pot is too big. They should also not be placed too deep. As the stems grow, you can lower it. Therefore hanging baskets works quite well. You just lower it as it grows.
I use normal pots, drill a few holes in the sides and lay it out with shade cloth. The baskets specifically for water plants are quite expensive.
When you plant them, cut off all the leaves to ensure that all the strength initially goes to the root system to establish them in the new environment.
Papyrus and palmiet can be planted in gravel with no soil, provided that there are enough fish/nitrates.
The "varkoor"/Arum lily is a bog plant and don't do very well inside the pond, and there are people who say that they are a bit poisonous to Koi, however, I don't believe that. They also don't transplant very well. I keep mine on the edges of my ponds.
The Water Iris do very well, they are hardy and easy to grow, and don't need any (messy)soil, and makes very nice yellow or blue flowers. (The blue flag is poisonous)
Dose all the plants with a triple dosage of potassium for an hour before you place them in the pond, to get rid of any possible parasites and bad bacteria.