Leaves rotting under the water
by Catherine MOrgan
(Lancashire,UK)
Doug says that the rotting is not because the leaves are at the improper depth - water lily leaves will actually adjust their stem length to the water depth.
Rotting leaves may be improper planting - if you covered over the crowns, you may find the existing leaves are rotting.
You don't say what kind of soil they are in (clay is best) or whether you dug this soil from the garden (herbicide residue?)
Here in Canada, planting too early into water that is too cold will do this as well. You don't say whether the water lilies are tropical or hardy forms so it's hard to say what the temperatures are needed in the UK and what they are at this time of year. If too cold, expect a setback (and moving from a warm greenhouse to cold outdoor water could do this as well)
If the crowns are above the soil surface, and none of the above conditions make sense to you, then you may have crown rot (take the plants back to the nursery where you bought them for an identification of this)
Good luck.
