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When choosing a pot for your waterlily, it's always a good idea to use something wider than it is tall to minimize the possibility of tipping over. Our favorite containers are Rubbermaid dishpans and totes, in sizes from three to ten gallons. In addition to being shallow, they have the added advantage of having lips or handles for easy handling and last for years.
Any sort of container will do though, including nursery pots, clay pots, oil changing pans, cat litter boxes and so on. Any with holes should be lined with several layers of newspaper (if you want the roots to escape eventually) or sheet plastic (if you don't want the roots to escape).
Soil can be most any that doesn't contain light material such as perlite which will float away. Most potting soils have light material so choose top soil if buying it in bags. We use and recommend "yard dirt", whatever you can dig up in your garden. In our case this is one step above beach sand, dug from the dune location of our next pond.
We wet the soil before placing it in the pot to aid in compacting it, important to prevent the plant from floating out before it becomes established. When the pot is full and compacted, we dig a hole (in the center for tropicals and to one side for hardies), loop existing roots into the hole and cover them with soil. Care must be given to placing the growth center exactly at soil level since burying it can cause damage to it and leaving it too high out of the soil will not let the new roots establish properly.
A note from John and Mary Mirgon: "Be sure to cut hardy waterlilies back to a healthy root stock. About three inches is the rule of thumb."
If using topsoil, a layer of sand should be added now to prevent the heavy soil from escaping into and fouling the water. Then add a layer of gravel or thin rocks to anchor the plant firmly in place. We use stones left over from the flagging we do around most ponds. These can be removed once the plant is established.
At potting we feed two PondTabbs to the average sized young plant and follow that with one Tabb per gallon of soil every four weeks if the water temperature is 70-80F, every two weeks if the water is above 80F. Large plants (10 gallon pots or larger) are fed weekly.
Propagating Viviparous Tropicals | Growing Waterlilies From Seed