A few months ago, our Lincoln County Extension office set a goal to improve our social media presence. We assigned specific posting days for our content areas (Agriculture & Natural Resources and 4-H), with an emphasis on educational content rather than just promoting events. After last week’s cold snap, I shared a post on Facebook about plant dormancy and why tree leaves change color and drop in winter. This week, I’d like to expand on that topic and explain what dormancy means for deciduous plants (those that lose their leaves) through the cold season.
When plants stop growing for the winter, we call them dormant—but there are actually two types of dormancy. Some plants enter endodormancy, which is triggered by the plant’s internal clock, and others enter ecodormancy, which is caused by external environmental conditions.
Plants enter endodormancy when days grow shorter and temperatures begin to fall. During this stage, the plant cannot resume growth until it has accumulated a certain number of chilling hours—hours spent above freezing, typically between 40–50°F. Even if the weather warms up, a plant in endodormancy will not grow until its chilling requirement is met. This protects the plant from “false springs,” preventing new growth during warm winter spells that could be damaged by a later freeze. Once chilling hours are satisfied, the plant shifts from endodormancy to ecodormancy and will begin growing again when temperatures rise. In other words, this system prevents the plant from “waking up” too early.
Other plants rely solely on ecodormancy. They go dormant when temperatures drop, but they begin growing again anytime environmental conditions are favorable. Because of this, they may produce new growth during early warm spells—growth that is vulnerable to freeze damage during the next cold snap.
During dormancy, a few things happen to a plant. Photosynthesis, respiration, and metabolism – processes which produce the energy a plant needs- slow down, causing plant growth to stop. Cold temperatures stop water from circulating through the plant, preventing the movement of nutrients and energy. To survive, plants store carbohydrates and nutrients in their roots before dormancy, providing the energy needed to survive winter and re-grow in the spring.
You may also notice deciduous plants changing color and dropping their leaves. As the plant prepares for dormancy, it absorbs nutrients from it’s leaves that are no longer needed for photosynthesis and growth. Chlorophyll (what makes leaves green) is broken down and removed, revealing yellow, red, and orange pigments in those leaves. Once the plant has absorbed as much as possible from its leaves, they are discarded. Leaves have a lot of surface area, which in the warm season, allow for maximum photosynthesis and respiration. In the winter though, surface area is bad – it allows more loss of water and energy from the plant. When plants drop their leaves, they are protecting themselves from cold damage and water losses.
In spring, longer days and warmer temperatures signal plants to come out of dormancy. Water, nutrients, and stored carbohydrates begin moving freely again. Roots grow deeper in search of water, branches extend, and buds swell and develop into new shoots, leaves, and blooms. Over time, the plant produces its full canopy and enters another growing season.
The dormancy process is more complex than what I’ve shared here, but it is an interesting phenomenon that allows perennial plants to survive from one season to the next. It’s also why we recommend that most pruning of plants occurs between January and February. In two weeks, I’ll talk a bit about evergreen plants, their adaptions, and why they don’t go through dormancy. If you have questions in the meantime, let us know at uge3181@uga.edu or 706-359-3233.
