So, what exactly happens to our trees, shrubs, perennials and grasses when they go dormant for the winter? Is it a kind of suspended animation and everything just stops? Or is there more going on beneath the surface?
Nature, by design, is efficient. So dormancy is a time period that helps the plant’s survival as it maintains a type of self-housekeeping and preservation. Periods of dormancy, sprouting, budding and growth are varied by plant type and species to ensure diversity and ecological balance of resources to help ensure survival and growth. In this two part series, we provide a general explanation of dormancy in Part I, then in Part II we’ll explore how dormancy affects specific plant elements.
Time for Plants to Chill
Vernalization is the physiological process in which certain plants and seeds need to go through a period of cold in order to germinate and/or blossom in the spring. The amount of cold time required for a particular plant or seed is referred to as chill hours. For example, fruit trees have high chill hour requirements, especially apple trees.
What actually triggers dormancy? As autumn begins, the amount of sunlight available begins to shorten and days become cooler. The drop in temperature slows down a plant’s metabolism and in conjunction with less sunlight, causes photosynthesis and respiration to slow, halting any growth.
In the summertime when sunlight is ample and days are warm, photosynthesis is at its peak, converting light energy into chemical energy, which is later used to fuel cellular activities. The chemical energy is stored in the form of sugars, which are created from water and carbon dioxide. Plants make more glucose than they actually need during the summer months, so they turn the excess into starch, which is stored until later, when it’s needed as they start to shut down their food production.
As food production ceases, plants move their stored starches from their leaves down to the roots for nourishment during the winter months. Dormancy is essential to a plant’s preservation in cold weather. If active growth continued during the winter, the water in a plant’s base, stems and leaves would freeze, significantly damaging its structures.
As the cold freezes the cells in a plant, it interrupts the pathways needed for nourishment and water to flow. Additionally, access to water becomes scarcer during winter due to ground freezing. Dormancy is also a time for plants to perform some self-maintenance; for instance, proteins are broken down and re-made, cell membranes are maintained, and leaves that may be damaged by disease or insect infestation die off and drop.
Up next, Part II of our Plant Dormancy series!