The alternation of light and darkness during a day is called the photoperiod. In addition to inducing plant flowering, photoperiod also affects the elongation of plant flower stems, the formation of roots and leaves, the dormancy of buds, and the shedding of leaves.
However, many people are aware of the importance of light, but most of them not really know about darkness. Many of my friends also having questions about whether the plants need darkness to grow?
Plants are like human beings, they will need to rest during nighttime. Even though plants won’t need long sleep hours as we do, but periods of darkness are required for plants. Plants reduce the photosynthesis process when it is dark. This helps to reduce water evaporation and nutrient loss so that they can grow and survive even in a bad environment.
Can Plants Survive Without Darkness?
Darkness tends to be not so important for the survival of most plants. As we know, plants obtain energy for growth through photosynthesis. Chlorophyll on the leaves absorbs sunlight to produce nutrients, they will ensure the roots and leaves of plants can absorb nutrients, thereby promoting growth.
The growth of plants is inseparable from sunlight, carbon dioxide, and water, all of which are indispensable. Sunlight is also the most critical factor. If there is no light, the entire process of photosynthesis will be incomplete.
Therefore, light is more important for most plants compare to darkness. A short period of darkness is required as plants will need to rest as well.
How Many Hours of Darkness Do Plants Need?
Different types of plants will need different hours of darkness, it all depends on the plants. Generally, most plants need to be kept in a dark environment for about 8-12 hours a day. Otherwise, plants may not get to rest well and this will affect their growth.
For example, for orchid species, in the winter and spring seasons, it is necessary to maintain a completely dark environment for 12 hours a day at night, so that it is easy for orchids to grow their buds. Otherwise, it will affect the flowering.
Therefore, if you use grow light in your house, the light cannot be turned on all the time. You need to turn it off during nighttime so that it won’t affect the recess of the plants.
How Does Darkness Affect Plant Growth?
Let me explain why plants have a problem at night. Plants use sunlight as energy in a process called photosynthesis. They get energy by taking carbon dioxide. They then produce sugars and many other metabolites with the help of sunlight.
At night, there isn’t any sunlight so plants will have no energy in the dark. Plants need to store energy in the light to get through in the night. Many plants store energy as starch because starch can give a lot of calories to them.
So on the light day when plants receive sunlight, they produce starch. In the evening, when the sky turns dark, the plants start to degrade their starch and use it to support their growth and other needs.
The plant will use the starch that it produces and store during the day. It keeps on using the starch until at the end of the night, all the starch will be completely consumed by the plant.
How does the plant know how it can do this?
The plant knows how long the night will be. The plant can perform in this way is because it has a biological clock like human beings. Our body knows the time of day. For example, we wake up in the morning and we start to get sleepy in the late evening.
A plant also has a biological clock and this allows it to know how long the night is going to be until the next dawn. By knowing the time, the plant can decide how quickly to use its starch. Other than starch consumption, the plant uses its biological clock for many other things as well.
The biological clock can tell them what the time of the year is and decide when they’re going to flower. Besides, they also use the clock to tell them when autumn is coming and they will fall off the plant. They can do this just before the winter comes.
Plant Grow Taller in Darkness?
Some people are wonder why do some plants in the dark grow taller than those plants in the light. They are confused and think those plants need darkness.
Actually, this is not right. When a plant is getting not enough sunlight, the leaves are lesser and its stem may get elongated. They may look weak, fragile, and can easily break at any time.
Even the plants in the dark grow taller than the plants in the light, but this kind of growth is no healthy. It is equivalent to the growth of saplings and it can be very delicate. If you don’t move the plant to a sunny place in time, it will fall and break because it grows too tall and the stem is too thin to support.
Even though most of the plants require a certain level of sunlight to survive, their metabolic processes continue in the dark. An example of the process is known as the Calvin Cycle. This is a process that involves carbon that is captured and then converted into stored energy during the day.
Another process is called respiration. This is a process that will combine oxygen and stored food. It then turns into a nutrient for the plant. Due to photosynthesis, plants will generate oxygen during the day and consume oxygen at night.
Due to the internal circadian rhythm, although it is dark, plants can know if dawn comes. It will get itself ready for dawn at the cellular level, and then stimulate the chloroplasts by light.
No Plant Can Grow in Complete Darkness
You need to know that no plant can grow in complete darkness for a long time. Any plant will gradually die if not receive any light.
However, some plants can tolerate low light and managed to survive.
Here are some plants that just need low light:
- Boston Fern (Nephrolepis exaltata)
- Pothos (Epipremnum aureum)
- Snake Plant (Sansevieria rifasciata)
- Ivy (Hedera helix)
- Cast Iron Plant (Aspidistra elatior)
- Chinese Evergreen (Aglaonema spp.)
- Weeping Fig (Ficus Benjamina)
- Lady Palm (Rhapis excelsa)
- Money Plant (Epipremnum aureum)
If you want your plants to grow healthily, then you must understand the growth habits of the plant, as well as the sensitivity to the darkness. With this, you can provide more targeted light and dark treatments, so that the plants can grow their buds as you wish. You should not blindly increase the duration of light and neglect the dark treatment which may cause the plants not to bloom.