Winter dormancy prepares landscapes for spring
We are in the midst of a cold and snowy winter in Western Pennsylvania. As we look out of the frosty windows of our warm homes, we see our once lush landscapes barren and dark.
Why do our deciduous trees and shrubs look so stark during the winter months? What we are witnessing is the dormancy period of these landscape plants. Here’s a little bit of science behind dormancy.
Dormancy is the slowing or pausing of active growth in trees and shrubs. This period is a time of rest. Dormancy slows and pauses the processes of active living, such as the absorption of nutrients, water uptake and cell division, that result in growth and plant reproduction.
Deciduous trees and shrubs enter dormancy to prevent the loss of water and nutrients and to avoid damage from cold temperatures. Dormancy begins in response to several factors, the primary factor being the amount of time trees and shrubs receive light during the day (photoperiod). As daylight lengthens and shortens with the changing of the seasons, the amount of light trees and shrubs receive for photosynthesis fluctuates. Deciduous trees and shrubs can sense this change in light through receptors in their leaves known as photoreceptors that sense two types of light: red light and far-red light.
Red light is the highest during the long hours of daylight in summer. When red light is most prevalent, trees and shrubs grow and reproduce. The hormone auxin drives the active growing processes of trees and shrubs, which peaks during the height of red light availability.
Far-red light increases as the amount of daylight decreases. In synchrony with the change in daylight length and the amount of red light and far-red light being received, plant hormones work to prepare the tree or shrub for winter.
The hormone abscisic acid signals the trees and shrubs to stop using energy for growth, thus decreasing the production of auxin. In response, trees and shrubs pull water and nutrients into their centers. Next season’s buds form a hard, protective covering as they become dehydrated. A third hormone, ethylene, increases and begins to break down the leaves.
As leaves drop from the trees and shrubs, ethylene creates a hard coating at the leaf site, preventing water and nutrient loss and resisting diseases. Lastly, leaves detach from the trees and shrubs on a swirling journey toward the earth. Over time, the leaves decompose and recycle into nutrients for use by the trees and shrubs. Our trees and shrubs, now in their dormant state, will remain at rest until the days lengthen again.
The winter countdown may have begun in your mind, as the first day of spring will welcome us on March 20; however, consider enjoying a quieter pace while the natural world around us takes a break and waits out winter for longer, light-filled days — a good lesson for all of us.
Penn State Extension has additional information about dormancy at extension.psu.edu/what-causes-a-tree-to-enter-and-exit-dormancy.
If you have questions about dormancy, contact the Penn State Extension Master Gardeners of Butler County’s Garden Hotline at 724-287-4761, ext. 7, or email the Master Gardeners at butlermg@psu.edu.
Cynthia Michelini and Mary Alice Koeneke are Penn State Master Gardeners of Butler County.
