Does the Color of Light Affect the Zinnia's Growth?

Zinnia Growth Processes

• As annual plants, zinnias bloom for only a season so new seed plantings are required each year. In terms of lighting needs, zinnias fall within the short-day category, meaning flower buds grow more quickly under long periods of daylight, whereas actual flower blooms grow faster under short periods of daylight. Short and long periods of daylight mean 10 or more or 10 or fewer hours of dark, or nighttime, occur within a day’s time. During the daylight hours, zinnia growth processes rely on photoreceptor materials located on leaf and stem structures. These materials absorb different light colors contained inside sunlight.

Light Exposures

• Zinnia plant growth relies on the same physiological processes found in other plants. Zinnias require a certain amount of light per day as well as a certain quality of light during the daylight hours. Zinnias grow best in areas that receive full sunlight. These conditions make it easier for zinnia photoreceptors to absorb the red- and blue-colored energy waves that stimulate the plant’s flower growth processes. In effect, the amount of sunlight zinnias receive can affect how fast their flowers grow.

Red Effects

• Like most plants, zinnias use a certain group of photoreceptors -- known as phytochrome -- to absorb red and far-red light-wave energy from the sun. Red light waves play a significant role within a zinnia’s flower growth process. Within the color spectrum, each color generates a certain energy wavelength. Wavelength amounts appear in nanometer measurements, which equal one-billionth of a meter. Phytochrome receptors respond specifically to wavelengths within the 600- to 750-nanometer range, which produces red and far-red light emissions. Certain types of grow lights attempt to simulate red and far-red light emissions. Light from incandescent bulbs also produces energy wavelengths within this range.

Blue and Green Effects

• Plant leaves absorb blue light-wave energy through two groups of photoreceptors known as cryptochromes and phototropins. Cryptochrome receptors capture energy from blue and green light waves as well as from UV-A energy wavelengths, while phototropins absorb green light. These photoreceptor groups respond to wavelengths within the 320- to 500-nanometer range, where blue, green and UV-A fields reside. Blue light waves encourage vegetative, or leafy, growth in plants. Because zinnias prefer full light exposure, these conditions encourage leaf growth, which is essential for the growth of buds and flowers.