In horticultural terms, plant sleep is called dormancy. Understanding dormancy is key to a water gardener's proper winter care of pond plants. A plant goes dormant because of changes in climate. These changes may take the form of a fluctuation in air or water temperature, a change in sunlight and daylength, or a variation in the amount of moisture the plant receives. Native climate is an important clue to a plant's dormancy requirement.
Heavy sleepers are usually native to colder regions.
In their natural habitat, the plants became accustomed to seasonally colder temperatures, lower light, and shorter days. These climatic changes signal the plants that it is time to stop growing completely for several weeks. During this period of dormancy, the plants put out no foliage whatsoever and appear to be quite dead. The less severe conditions to which the plants have adapted do not stress the plants to the same degree suffered by plants from a colder region. Plants from a temperate realm have the ability to go dormant, but may not need to do so in order to survive and grow through succeeding years.