December 21, 2023, marks the winter solstice, the day of the year with the least amount of sunlight. Conversely, this day marks the summer solstice in the Southern Hemisphere; their longest day of the year. The winter solstice in the Northern Hemisphere occurs because, as the Earth spins on its axis around our sun, the North Pole is tilted away from the sun at approximately 23.4?. On the days following the solstice, the Earth will gradually tilt in the opposite direction until the summer solstice occurs six months later.

The solstice has been recognized and celebrated for millennia. According to History.com, neolithic monuments such as Stonehenge and Newgrange are evidence of human acknowledgement of the solstice as far back as 10,200 BC. The ancient Romans celebrated Saturnalia during the solstice, honoring Saturn, the god of agriculture. Many other ancient cultures recognized the solstice as the turning point of the dark days of winter, including the Incas, Scandinavians, and Persian Zoroastrians.  

What happens to our deciduous trees and plants during these darkening days? They go into dormancy, a state that may look like death to the casual observer, but is far from it. Plants have developed dormancy as a way to conserve energy, water, and nutrients, and to avoid damage caused by cold weather. As the Earth tilts further away from the sun, and the days grow shorter, the tree's photochromes sense that they are receiving less light. This triggers the production of abscisic acid, a hormone produced in the root of the tree. Abscisic acid is responsible for the amazing process a tree goes through to prepare for dormancy, and is evidenced by the changing colors of the leaves. Rather than wasting the vital nutrients used for photosynthesis stored in the leaves, abscisic acid ensures that they are reabsorbed back into the structure of the tree.

The reabsorption process triggers two additional hormones, auxin and ethylene, to get to work. Auxin is the hormone responsible for the growth of the plant. As water and nutrients are absorbed back into the plant auxin levels decrease, which activates ethylene. After the reabsorption process, ethylene produces a hard crust between the tree and the leaf. This creates a type of scab to avoid water and nutrient loss, and to prevent pathogens from entering the tree. The existing buds on the plant form a hard shell, encasing the tender growth beneath, and the leaves detach from the tree. The tree will remain dormant until the daylight grows longer, activating auxin to restore the growth process.

The process of winter dormancy and “rebirth” in the spring is life-affirming and hopeful. Even during our darkest days; at our coldest and wettest, we can look forward to a future of longer days, warmer weather, and the budding of new life.