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If you are a gardener, you may have noticed that tiny plants in your garden suddenly shoot up overnight and wondered if plants really do grow in the dark or if you simply imagined the sudden growth spurt. The truth is plants do grow more rapidly during the night when it is dark. Find out why.
Plants grow in both daylight and darkness, but for many, the most rapid time of growth is during the night. When the plant rests from the hard work of photosynthesizing the energy from the sun, the plant cells are then free to perform other tasks. At night, the plant cells convert the stored energy to growth hormones that, in turn, activate active plant growth. Plant stems elongate the fastest just before dawn.
Daylight and darkness aren’t the only things that affect a plant’s growth rate. Other environmental factors like temperature, moisture, and nutrients are also integral to plant growth. A plant that has all its needs met will flourish and tends to grow fastest at night when it is dark.
When do plants grow?
Plants grow during both the day and the night, but the most rapid growth is usually at night. During the day, the plant is busy performing photosynthesis and taking care of basic needs like controlling the plant’s temperature and hydration. At night, the plant’s cells are freed to attend to plant repair and cell expansion (growth).
Why do plants grow fastest at night?
During the day, the plant’s cells are busy harnessing the energy from the sun in a process called photosynthesis. Through photosynthesis, the plant uses the energy from the sun to manufacture glucose. Some glucose is used right away to regulate the plant’s temperature and hydration during the day. Excess glucose is stored for future use.
When the sun goes down and the plant’s cells are no longer working hard to make food, they use the stored energy (glucose) for plant repair and growth. This is when the plant cells divide and expand to create new plant growth.
While scientists aren’t sure of the exact process, it appears plants not only grow fastest at night, but they also are able to anticipate the arrival of dawn. Plants like sunflowers orient their flower heads toward the sun’s direction long before the sun appears on the horizon.
Do plants grow during the day?
Plants do grow during daylight hours, but the growth rate is slower than nighttime growth. During the day, the plant’s cells perform photosynthesis and use the energy to take care of basic needs like controlling the plant’s temperature and hydration.
Environmental conditions affect the growth rate during the day, too. If the plant struggles to maintain hydration or regulate temperature, it will have less energy available for plant growth.
Can you give indoor plants too much light?
Growing seedlings or houseplants under artificial lights help them get the necessary light to manufacture energy (glucose) for the plant. Without adequate light, plants cannot make the energy they need for healthy growth. However, too much light can interfere with plant growth. Plants need darkness in order to convert the stored energy into cell division and expansion to grow.
It is always best to check the light requirements for your specific plants and use them as a guide for using artificial lights. Too many hours of light may cause your plants to work longer and make glucose, but they may have less time to tend to necessary tasks at night, like repair and growth.
Will plants grow faster if you keep them in the dark?
Although plants grow fastest during the nighttime hours when they are in darkness, they cannot grow without light during the day. Plants need light to perform photosynthesis, the process of converting sunlight into energy for the plant.
When plants receive light during the day, the plant cells are busy all day making and storing glucose for growth and other plant functions. Without energy, your plants cannot grow.
When the sun goes down, the plant cells are freed to utilize the stored energy for cell repair and expansion, which results in what you observe as plant growth. Plants need both daylight and darkness to flourish. They cannot survive without light during the day.
What else do plants need to grow?
Plants need water, nutrients, and light to grow. But they also need air, the right temperature, and suitable humidity levels. Each affects the rate of growth of your plants. Consider these factors and how they affect your plants’ growth rate. You can also try different types of water we’ve written about, like:
How Water Affects Plant Growth
Water plays a vital role in plant health and growth. Water is necessary for transporting nutrients, maintaining turgor (the pressure inside the plant cells that keeps them rigid), and is needed for photosynthesis.
Water helps to cool the leaves of plants during transpiration, regulates the opening and closing of stomata (pores on the leaves that open and close to allow for the transfer of gasses), provides the pressure needed for roots to grow into the soil, and works as a solvent for carbohydrates and minerals in the plant.
Without adequate water, plants wilt and eventually die. The fastest plant growth occurs when the plant has a good supply of water to perform photosynthesis and transport nutrients to all plant parts.
How Nutrients Affect Plant Growth
Plants need adequate nutrients to thrive and grow; in fact, they need 17 essential nutrients for proper growth. They get oxygen, carbon, and hydrogen from the air or from water, but the others must be present in the soil.
Nutrients plants need to grow are classified as macronutrients and micronutrients. Macronutrients are needed in relatively large amounts, while micronutrients (sometimes called trace elements) are needed in much smaller amounts.
What macronutrients do plants need to grow?
Macronutrients are the nutrients plants need in relatively high amounts. They are the three nutrients listed on plant food or fertilizer. Nitrogen (N), phosphorus (P), and potassium (K) are macronutrients and make up the N-P-K formula of plant food and fertilizer. These nutrients work together to build healthy foliage, fruit, and flower development, and strong roots.
Plants perform best when they have a balanced supply of the macronutrients nitrogen, phosphorus, and potassium.
What micronutrients do plants need to grow?
Micronutrients are also needed for healthy plant growth, but they are required in smaller amounts. Micronutrients are also called trace elements. Many trace elements can be found in the soil naturally. Micronutrients include zinc, iron, manganese, copper, boron, molybdenum, chlorine, and cobalt.
In the event your soil lacks the trace elements needed for healthy plant growth, you can purchase micronutrients separately and amend the soil. Traditional commercial fertilizers do not contain trace elements, but formulas are available.
How Light Affects Plant Growth
Sunlight is necessary for the plant to perform photosynthesis and make energy (glucose) to regulate plant functions and produce plant growth. How much light the plant needs depends on the type of plant you are growing.
Plants are divided into three groups (long day, short day, and neutral day plants) according to the amount of daylight and darkness they need to promote blooming and fruiting. Long-day plants bloom and set fruit when the days are long and the nights are short, while short-day plants bloom when the days are short and the nights are long. Neutral-day plants do not depend on the length of the day to flower and set fruit.
Calling them long-day and short-day plants is actually a bit deceiving as it is actually the number of hours of darkness the plants receive that spurs blooming and fruiting, not the number of hours of sunlight. Some vegetables, like onions, will not form bulbs if they do not receive the right amount of darkness at night. To produce large, tasty bulbs, you need to grow long-day onions in northern climates and short-day onions in southern climates.
Many flowering plants bloom according to the hours of darkness they receive. Houseplants, like Christmas cacti and poinsettias, will not bloom unless they are exposed to 12 hours of complete darkness at night for several weeks. Likewise, many perennial flowers bloom at the same time every year because they need a specific amount of darkness at night.
How Temperature Affects Plant Growth
Temperature is also essential to plant growth. While temperature preferences differ from plant to plant, each grows fastest when the temperature is suitable for the plant. As a rule, plants do best when there is a 10 to 15-degree difference between day and night, but there are exceptions.
Plants exposed to high temperatures during the day need to expend more energy to keep the plant hydrated and cool the plant through transpiration. When this happens, the plant cells do not have as much energy left at the end of the day to promote rapid growth.
Plant growth, even at night, may be slowed due to high temperatures or drying winds during the day. When the temperature is suitable for the plant (and it gets adequate sun and water), it stores energy during the day and uses it for cell repair and expansion, causing rapid plant growth at night.
How Humidity Affects Plant Growth
Humidity levels affect the plant’s ability to maintain turgor and proper temperatures. If the air around the plant is too humid, it may struggle to release oxygen and moisture during transpiration. If the humidity level is too low, foliage may become too dry or even damaged. The plant may then need to expend more energy on cell repair and have less energy left over for cell division and expansion, resulting in slower growth.
How Air Affects Plant Growth
Under normal conditions, plants access carbon dioxide from the air to perform photosynthesis. Although it is unlikely the air surrounding your plants lacks enough carbon dioxide for the plant to grow well, it is still a vital need. Drying winds can stress plants and hinder growth, too.
Related Questions
Can you force fall-blooming perennials to bloom earlier?
Like mums and asters, many perennials bloom in the fall when the days are short and the nights are long. You can force them to bloom earlier in the summer by covering the plant with a box or other object before the sun goes down and leaving it covered until morning. While this may not be practical in a flowerbed, it is an easy way to force potted perennials to bloom at the desired time.
Many flowers purchased in greenhouses and florist shops have been forced into bloom by controlling the number of hours of darkness the plants receive. This is often true of holiday plants and early-blooming mums and asters in late summer.
Will putting my plant in complete darkness make it grow faster?
Plants grow faster at night when it is dark, but they need sunlight to perform photosynthesis and make energy for the plant. Putting a plant in complete darkness for more than 12 hours every night will not make your plants grow faster.
Without sunlight (or artificial light), your plants will soon die because they will be unable to make the glucose they need for growth. Forgetting to uncover a plant for a day or two won’t likely cause severe damage to the plant, but subjecting it to darkness for long periods in the hopes it will grow faster will.
Plant cells work hard all day, transforming the sun’s energy into the glucose the plant needs. Most of the energy is stored for future use. While they do grow during the day, of course, plants tend to show the most rapid growth at night when it is dark. Because the cells are freed from the task of performing photosynthesis, they can devote time to cell repair and expansion during the night.
Sources
- https://ucsdnews.ucsd.edu/archive/newsrel/science/2011_07evening-complex.asp
- https://extension.oregonstate.edu/gardening/techniques/environmental-factors-affecting-plant-growth
- https://edis.ifas.ufl.edu/pdf/4H/4H36000.pdf
- https://ocj.com/2021/07/understanding-primary-factors-driving-plant-growth/
