Do Plants Need Darkness? Let Us Shed Some Light on This
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Sunlight is Important
All forms of plant life except those that depend on others for their nutrition need sunlight during the day. Plants make their own food and are called autotrophs. They make use of a process called photosynthesis to manufacture energy. Sunlight is a major constituent along with other essential components from the air, soil, and water.
This energy is produced in unique cell organelles called chloroplasts, mostly concentrated in the green leaves. Now, just like sunlight, plants also need a period of darkness to regenerate another significant protein compound called Phytochrome effectively.
When we light up our green space at night, we hamper the plant’s ability to produce this compound effectively.
Why Is Phytochrome Necessary?
Phytochrome plays a vital role in crucial processes such as:
Leaf Abscission and Dormancy
All plants shed their leaves and enter a period of dormancy. When plants are denied darkness, phytochrome produced by it delays the production of abscisic acid responsible for both abscissions and dormancy. Light during the night time fools deciduous trees into retaining the chlorophyll in its leaves. This can adversely affect their growth in two ways.
- Instead of retaining leaves, the tree in the darkness had to turn its photosynthesized compounds into various sugars and brought down all that nutrients to the roots before shedding its leaves.
- When trees continue growing even in the Fall because they were exposed to light in the dark, they store little or no food in their roots and fare poorly in the winter.
Plants have an innate ability to measure the length of the night (darkness period). With this, they can schedule their blooming, seed germination, and leaf dropping in autumn.
An experiment was conducted way back in 1938 with a cocklebur plant. The plant blooms only when nights are longer than the day. The plant was exposed to 1 to 2 minutes of light at night with a 25-watt incandescent bulb that was lit over it. It was noticed that the plant’s flowering was poor.
Every short-day plant such as strawberries, primroses, and some varieties of poinsettias and chrysanthemums require undisturbed darkness to bloom in their respective season.
Germination of Seeds
Phytochrome also plays a role in seed germination. In 1996, Professors D.G.W. Edwards and Y. A. El-Kassaby experimented on the Tsunga mertensiana (Mountain Hemlock) plant that concluded that plants' overexposure to light reduced its seed’s germinating ability.
Therefore, daily periods of darkness play a vital role in the proper growth of plants. Planet follows a biological clock called the circadian rhythm. It is this that helps them anticipate dawn and prepare their chloroplast for light stimulation.
Light and darkness are both needed in proper measures to trigger different processes in plant growth, behavior, and metabolism. It also determines the leaves and distribution of chloroplast on them.
An intimate relationship between plants and light
A lot of food growers and horticulturists in warmer climes begin with seeding indoors. This is mainly because some plants can grow well in ambient light itself. Extra light not just hampers growth but can also be detrimental to their germination.
Effect of Infrared light waves on plants
Stem: Infrared light waves increase the speed of stem growth. It can also increase the growth of the internodes on them. However, it has been noticed that plants exposed too long to this red light in the spectrum develop awkwardly long and skinny stems.
Flowers: The A&M University in Texas, USA, published a study stating that infrared rays may be necessary for blooming. Some plants do not bloom under ordinary home lighting conditions because it does not contain enough infrared radiation.
Large quantities of light have the potential to irreversibly damage plants. Artificially created infrared light rays can burn plant cells or dehydrate them. Studies have shown that it can trigger abnormal growth in them and force them to bloom earlier by using up all its stored resources. Plants can become spindly too.
Avoid unnecessary light
During nights, your plants need darkness. If you have installed lighting in your patio that illuminates the green patch, make sure that you off them once you retire. If you have a neighbor who uses his patio or garden lights for outdoor plants, you may have to talk to them about letting your plants get some darkness.
The shade cloth
Watch this video to understand how you can use it to cover your nursery to shield your plants from unwanted lights. You can directly cover your plants with it as well.
How to set it up
Shade cloth is something that farmers ordinarily use to cover their plants in dry and arid areas where temperatures in the day can reach above 100°F.
However, you could also use a shade cloth framework to cover your plants at night. It can be conveniently drawn over a small green space if shutting off light pollution if artificial lighting cannot be avoided.
There are many grades; ideally, you must go for a shade cloth that blocks 70% of light. You will need:
Measure PVC pipes or circular hoops and create a sturdy framework. Measure the shade cloth and cover it with it. Use tie wraps to secure the shade cloth to the frame. You may use anchor points in your garden like tree trunks to secure the shade cloth by tying a knot and removing them during the day.
Darkness is essential for plants. Nighttime is not a useless time for them since a lot of growth processes take place at night. Plants do not sleep as animals do. Plants continue to respire and grow through the night.