The longest night and the shortest day of the year are behind us. Gradually the days will get longer adding an extra minute of light each day. This rebirth of light has influenced our mythology and our lives since Neolithic times. Many cultures throughout history have honored a sun god or goddess as he or she restores sunlight to the world. Christ’s Mass is the time-honored Christian tradition of welcoming the Light back into the world. Chinese, Japanese and Koreans celebrate balance and harmony as positive energy increases with the longer days. Hanukkah is known as the Festival of Lights.
Light plays an important role in the life of plants. I mentioned the miracle of photosynthesis a couple of weeks ago. Light, its intensity, duration and quality, influences flower initiation, flower development, flower number and size, seed germination, bud-break, stem elongation, leaf-fall, branching and many other plant processes. Shade grown plants can have longer distances between joints (internodes), thinner paler leaves and fewer side shoots. Sunflowers follow the sun throughout the day, turning their heads toward it. These light responsive (phototropic) mechanisms in plants are adaptations to their environment.
Terms such as “direct,” “morning” or “afternoon sun,” or “sun,” “partial sun” and “shade” refer to light intensity. Temperature often limits what light intensity a plant can take. Plants may tolerate full sun in cool summer climates but require shade in hot dry climates such as ours.
Light duration is the amount of time a plant is exposed to sunlight. The “24-hour” light of Alaska’s summer allows huge vegetables to grow even under cool temperatures. Developmental stages of a plant are often influenced by daylength, such as poinsettias needing very short days to bloom.
Light quality is the color or wavelength that reaches the plant’s surface. Red and blue wavelengths have the most impact on plant growth. Blue is responsible for vegetative leaf growth. Red encourages flowering. Fluorescent cool white lamps work well for starting seeds indoors. Indoor flowering plants do better with broad-spectrum fluorescent bulbs.
However, plants aren’t the only things influenced by light – so are gardeners. My friends and I celebrate December 21 and the start of longer days. It seems counter-intuitive that with the start of winter, the days get longer, but after a week or two, I can definitely tell light lasts longer each day and I feel spring is that much closer. Happy New Year!