Here is what Mastersons says in their online item. I may want to
divide my colored ones that have not jumped the pot..

dividing hardy water lilies

Hardy water lilies should be divided every two to three years,
depending on the size of the container they are growing in. Early
spring is the best time, but hardy lilies can be divided any time
during the growing season.

Check your lilies. If the pots are bulging out at the sides, or the
lily tubers are hanging out over the top of the pot, it is time to
divide. You may also notice smaller and fewer leaves and flowers,
this can also be a sign that it is time to divide and repot.

The best container is a five to seven gallon pot that is wide and
shallow.

Here are five easy steps to get your lilies growing and blooming
again:

â– Carefully remove the plant from its existing pot (you may have to
cut
the old pot away). Gently wash the soil away with a garden hose to
expose the tuber, roots and growing tips.
â– Examine the tuber, you will see the newer growth on one end that
includes leaves, flower buds and roots. Often there will be more than
one end with good growth and roots. Select the best looking piece(s)
and cut to 3-5� long with a sharp knife, keeping the end with good
roots and top growth. Trim off excess roots (leave the white,
emerging roots), all older and damaged leaves and all flower buds.
The ‘new’ plant must put most of its energy into developing
a new root
system, not making leaves and flowers right away.
â– Partially fill your container with an aquatic soil or heavy garden
soil, not traditional potting soil that includes peat and vermiculite
or perlite. If there are large holes in your pot, line it with burlap
or weed fabric first to keep the soil from washing out through the
holes. Push the tuber down into the soil at a 45 degree angle, with
the cut end down and near the side of the pot. This will provide the
most room for your new plant to grow. Place three aquatic fertilizer
tablets, into the soil about half way down, equally spaced around the
pot. Add more soil as necessary, press it around the tuber and roots
but do not cover the growing tips. Finally, add a layer of pea gravel
on top, this will help to keep your fish from digging at the roots and
will hold the soil in place.
â– Slowly submerge the pot into your pond. It is best to start it in
shallow water (6-12�) until the first few new leaves appear, it can
then be lowered to depths up to three feet. You will likely notice a
little cloudiness in the water from the soil but this will settle out
quickly.
â– Fertilize your lilies every four weeks during the growing season w
ith
3-4 tablets. Push the tablets 1-2� down into the soil, away from t
he
tuber. Remove spent flower buds and old leaves throughout the season
as necessary.