Do Plants Need a Day Night Cycle?

reviewed by Christina Lopez

Studies in botany are almost as vast as that in human anatomy. Being an integral part of our life, plants provide us with nutrients, food, biofuels, environmental protection, and help a country maintain economic productivity. With innumerable blessings comes great responsibility. The responsibility of protecting and nourishing plants as they nourish us.

Day Night Cycle

Day Night Cycle
Day Night Cycle

Researchers have catered to almost all aspects of a plant's well-being, including a plant's circadian rhythm, that is, the day-night cycle. Plants require a set day-night cycle, as do humans. However, the amount of light and darkness required varies from one species to another.

The branch which deals with this outlook is called Photoperiodism. It is the physiological reaction of plants to different lengths of light and dark periods. Plants use this clock to be able to monitor day length and thus can prepare for seasonal changes. We classify plants as long-day plants, short-day plants, and day-neutral plants based on the amount of light or darkness they require.

As the name indicates, a long-day plant needs more than 12 hours of sunlight or less than 12 hours of uninterrupted darkness to generate the production's reaction. These plants produce flowers in the mid-spring and summers when the days are longer, and they can get maximum sunlight. Long-day plants include lettuce, petunias, and spinach.

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On the other hand, a short-day plant is the one that needs less than 12 hours of sunlight or more than 12 hours of uninterrupted darkness to produce a flower. These plants include chrysanthemums, poinsettias, marijuana, rice, and Christmas cactus. Contrary to popular belief, if we expose these plants to excessive light, they will decay.

It was a widespread belief that the amount of sunlight a plant receives determines its ability to bloom or produce a flower. However, recent studies have proved that the length of darkness is more crucial than sunlight, which confirms that every plant needs a day-night cycle exclusive to it.

A neutral-day plant

A neutral-day plant is not affected by specific photoperiods, and they initiate flowering only when they reach a specific age or maturity. These include cucumbers, rose, tomatoes, etc. This classification reveals the significance of day-night circadian rhythms in a plant.

Now the question arises if the plants that require maximum sunlight take a rest at night? The botanists and the plant's physiology says no! During the day, plants take up sunlight during photosynthesis and transform it into chemical energy; that is, they convert water and carbon dioxide into glucose. When the sun goes down and darkness prevails, plants utilize this chemical energy for other metabolic processes, including growth. In short, plants also have a robust chemical life, which helps them adapt to their environment in addition to the day-night cycle.

It was also commonly known that increasing the hours of light a plant receives also increased its yield. Some gardeners use grow lights to provide their plants with 24 hours of uninterrupted light. However, botanists recommend not to do so. Leaving plants in a continuous source of light for 24 hours will decay its cells, and the process of respiration will be hampered, ultimately leading to the death of the plant. Even the long-day plants need less than 12 hours of darkness. If a long day plant is exposed to 12 hours of light with no sign of growth, the first thing to do is increase the light for up to 18 hours. If the growth is still not up to par, then a stronger grow light is needed, which has increased intensity. The ideal intensity of light for vegetative plants that bear fruits or flowers is around 20 to 40 moles of light per day. Adding nutrient-rich fertilizers to the soil is also useful in such a case.

Another critical factor that needs to be addressed is if the grow lights remain turned on accidentally for a longer duration than needed! However, if the plants are in their vegetative (growth) phase, the decay process will not start. However, plants must be out of light for some time for them to perform respiration. Photosynthesis can take place only in sunlight, whereas respiration can also start at any time. Still, it is accelerated during darkness as it is nature's way of telling the plant to rest, eat, sleep, and be prepared for the next day to make food. So the concept that more light equals more yield is not endorsed by experts, and it is better to stick to the approved plant growth requirements.


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About Christina Lopez

Christina Lopez grew up in the scenic city of Mountain View, California. For eighteen ascetic years, she refrained from eating meat until she discovered the exquisite delicacy of chicken thighs. Christina is a city finalist competitive pingpong player, an ocean diver, and an ex-pat in England and Japan. Currently, she is a computer science doctoral student. Christina writes late at night; most of her daytime is spent enchanting her magical herb garden.

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