Water lilies, plants of the genus Nymphaea, are common sights in ponds and tranquil bodies of water, known for their large, floating pads and striking blossoms. The immediate answer to whether these pads die in winter is yes; the visible parts of the plant do die back completely. This dieback is a natural, annual process, but it does not mean the entire organism perishes. The plant has evolved a successful strategy to survive the cold months below the water surface, ensuring its return when the weather warms.
The Seasonal Cycle of Water Lilies
The decline of the lily pads is initiated by two main environmental cues: shortening daylight hours and cooling water temperatures during the autumn. Water lilies are highly sensitive to these changes, which signal the end of the active growing season. Once the temperature of the water drops consistently, the plant ceases the production of new leaves and flowers.
The existing, large pads, which were responsible for photosynthesis throughout the summer, begin a process called senescence. They yellow, lose their structural integrity, and eventually decay. This decomposing plant matter sinks to the bottom of the pond, where it will break down over time.
By late fall, all that remains of the water lily at the surface is the submerged stem structure leading down to the soil. This visible disappearance is often mistaken for the plant’s death, but it is actually a crucial step in preparing for the cold. The entire process of dieback is a deliberate biological action to shed vulnerable, energy-consuming foliage before freezing conditions arrive.
How the Rhizomes Survive Winter Dormancy
The non-visible part of the plant, the root structure, is where the water lily’s survival mechanism resides. Hardy water lilies develop a thick, fleshy underground stem structure known as a rhizome or, in some cases, a tuber. This structure serves as the plant’s food storage unit, packed with starches and sugars synthesized during the summer months.
The rhizome enters a state of dormancy, a period characterized by a significant slowdown in metabolic activity. This reduced-energy state allows the plant to sustain itself using its stored reserves throughout the winter without requiring light or nutrients from the water column. The rhizome essentially goes into a deep sleep, conserving its energy until spring.
For survival in freezing climates, the placement of the rhizome is crucial. In natural ponds or deep garden features, the rhizome remains submerged at the bottom, safely below the depth at which the water freezes. Since water is densest at 4 degrees Celsius, this warmer layer settles at the pond floor, insulating the rhizome from the ice layer forming at the surface. This protective, non-freezing environment allows the dormant rhizome to wait out the harshest temperatures.
Distinguishing Hardy and Tropical Varieties
While the dieback process is common to most water lilies, their ultimate fate in winter depends entirely on the specific variety. Hardy water lilies (Nymphaea hybrids suitable for temperate zones) are perennial and rely on the dormancy mechanism of their submerged rhizomes to survive the winter. These varieties will naturally reappear year after year, provided they are kept below the ice line in deep water.
Tropical water lilies, by contrast, are native to warmer climates and lack the genetic hardiness to withstand extended periods of cold. They will continue to grow and bloom until the water temperature drops below about 60 degrees Fahrenheit, often much later into the fall than hardy varieties. However, in regions experiencing freezing winters, the tropical varieties must be treated as annuals or manually lifted and stored.
If a tropical lily is not brought indoors or protected in a warm environment, the rhizome will likely freeze and die. Gardeners who wish to save these tender perennials often harvest the small tubers that form, storing them in a cool, dark, and slightly moist environment until spring. This distinction explains why some water lilies return reliably each year and others require intervention or replacement.