All hardy water lilies overwinter perfectly well, if their rhizomes do not freeze completely. Since water lilies come in different sizes – miniature, small, medium and large – their winter care primarily depends on their vigor and type/depth of your water feature. While miniature water lilies are best grown in shallow waters, their more vigorous counterparts prefer the deeper end of a pond.
In natural ponds large water lilies are generally planted 1-1.5 metres deep. The thickness of the ice layer on large ponds rarely exceeds 1 metre even in the most severe winters, when temperature keeps at around -30oC for a couple of weeks, so the water lilies are safe at the bottom of large water features.
When large water lilies are planted less than 1 metre deep, or if a particular water feature tends to freeze to the very bottom in winter, the safest way is to plant them in aquatic baskets. When the winter sets in, they [banner] should be moved either into the deeper end of the pond or a cool cellar (basement), whichever is more appropriate in your case. The basket with the water lily should be stored submerged in a container filled with water.
The same rules apply to the medium, small or miniature water lilies. If you do not have a basement, after being carefully rinsed and soaked in the Previcur fungicide, rhizomes could be stored in damp peat or moss in the fridge.
© Giedra Bartas, 2009