JRB wrote:

Hello all,

As it is winter here (UK) and the leaves have all died off, I thought it
was time I pruned my water lilly but when I lifted it from the pond it was
a mass of roots, etc. It has literally consumed the pot it was in. The
rootball must be 50 time bigger than when I bought it a couple of years
ago.

That's normal.

Please can anyone help with tips on the best way to prune, propagate, etc
as I haven't done anything like this before. I can see some new plants
among the roots that I imagine can be propagated.

Go wild! Cut it at any point between crowns (the growing tips). You can
keep or discard any large portions without crowns - discarding them will
slow down growth at the beginning of next growing season, but mean you
won't need to do this again too soon.

Find someone else who wants a lily or five :-) Then put as many as you want
back in the pond _bare root_, and wired to a rock or other good weight.
Some people find their lilies don't thrive that way, but it sounds like
yours is essentially bare-root already and doing fine, so it'll really
simplify things next time you need to divide them. I like to keep them
bare-root to get maximum extraction of nutrients from the pond.

Lilies are extremely tolerate of being divided and yours is super healthy,
so you should have no fears about being extreme.
--
derek