Overwintering water lilies isn’t all that difficult.
There is only one major rule you have to remember, don’t freeze them.
They might survive freezing, but the odds are that they wont.
Growing in Depressions in the Liner?
If your lilies are growing in plant holes formed by the liner, then you need do nothing as the ground heat at the bottom of the pond will likely stop the rhizome from freezing solid.
Trim off the foliage and your fall plant-related work is done.
Overwintering Hardy Water Lilies In Pots
If your lilies are growing in pots, then you have two choices after you’ve trimmed back the foliage.
- You can either drop the pot back into the deepest part of your pond to overwinter there (assuming the pond doesn’t freeze solid) or
- You can take the pot (lily and all) into a cool dark basement.
If you take it into the basement, a cold storage area works well but a heated basement does not.
Keep the lily rhizome damp all winter (leave it in its pot for ease of storage) as well as keeping it as cold as you can without freezing. A beer fridge also works well if you have no cold storage room.
I leave ours in their pots until spring (and divide them at that time) But I put the pot in a large waterproof “tray” and fill the tray with water.
The cool temperatures in the cold cellar stop the plant from growing and the water in the tray stops the soil from drying out.
In the spring when the ice is off the pond you can return your water lily to the pond.
And that’s all there is to overwintering hardy water lilies. (cool and damp but not frozen):-)