Does Sugar Really Help Plants Grow? Here's the Truth


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Photosynthesis
CREDIT: mapichai/Shutterstock.com

A number of different plant tips suggest ways gardeners can help their plants thrive and stay healthy all season. One of the more recent gardening myths circulating is related to giving plants sugar in order to help them grow.

But does sugar really help plants grow? The short answer is no–plants naturally use the process of photosynthesis to produce their own sugar—or glucose—as they need it. By additional sugar being added, no matter how little the amount, plants could potentially be harmed rather than helped.

It is important to note that individual plants may require more sugar because they are not healthy enough to produce adequate quantities of it on their own. However, alternative ways exist to help gardeners ensure their plants have the essential components they need to photosynthesize normally and be healthy again.

Understanding Photosynthesis

By basic definition, photosynthesis is the process by which plants manufacture their own food— mainly a form of sugar known as glucose.

To produce food, plants require “energy from the sun, carbon dioxide from the air, and water from the soil.” (Source: Oregon State University) During the process of photosynthesis, the plant’s chloroplasts in its mesophyll cells (located between the layers of plant leaves) split carbon dioxide molecules into carbon and oxygen atoms and uses energy from the sun and water from the soil to form carbohydrates (starches and sugars).

By the end of this process, the plant is left with sugar and oxygen. The plant will either store the carbohydrates, use them for energy, or create oils and proteins to use when there is low light or if their roots need nutrients.

Essentials for Healthy Photosynthesis

In general, gardeners can easily avoid raising an unhealthy plant by making sure it has all the essential things it needs to photosynthesize from the start of planting: sunlight, water, and air.

Sunlight

Chlorophyll, which is the pigment that makes a plant’s leaves look green, is responsible for capturing light energy from the sun. The light energy triggers a chemical reaction in the plant’s chloroplasts that helps break down the carbon dioxide molecules into carbon and oxygen atoms.

In general, the more sunlight to which a plant has access, the more energy the plant can get from photosynthesis. However, the maximum amount of light a plant requires will differ for each species. Most garden crops, such as tomatoes, respond well to maximum sunlight, while other indoor plants may require less sunlight in order to photosynthesize. 

Water

Water is essential for all forms of life, so it is no surprise that it is a vital ingredient plants need for photosynthesis. Most plants take in water by pulling it through their root systems from the soil.

Depending on the environment, a plant’s natural access to water can differ. Gardeners should factor in the region in which they live to determine how much and how often plants need watering. As a rule of thumb, most plants require more watering during hot or dry periods.

*Note: Although water is a crucial ingredient needed for photosynthesis, it is also essential for the transportation of nutrients, regulating temperature, and keeping plant cells turgid, or stiff.

Air

Just like humans, plants require gases to live, and they need carbon dioxide more than anything. Carbon dioxide enters the plant through the tiny pores—called stomata—in its leaves, flowers, branches, stems, and roots. (Source: Smithsonian Science Education Center)

Plenty of carbon dioxide exists in the air, so it is difficult not to have enough of it for plant growth. However, carbon dioxide is consumed very quickly during the process of photosynthesis, while it gets replenished very slowly in the atmosphere.

This can be a problem for greenhouses that are tightly sealed and do not allow enough air from outside to enter. However, most commercial gardeners overcome this by installing a carbon dioxide generator in the greenhouse. Gardeners with home-based greenhouses can use dry ice as a source of carbon dioxide for their plants.

Temperature

Although the temperature is not necessarily a significant factor that influences the process of photosynthesis, it should still be kept in mind. Photosynthesis typically occurs at its highest rate in temperatures between 65 and 85 degrees Fahrenheit. Any lower or higher, and the rate decreases—but even then the process will not come to a complete stop.  As long as light is available, photosynthesis will happen.

The Root of the Sugar Myth

Sugar Cubes

The idea behind using sugar to help aid in plant growth comes from observing plants’ natural process of photosynthesis. Since plants use photosynthesis to create sugars and starches for food, then we can logically assume that if more sugar is added to a plant, then it is being provided with additional food, and thereby boosting growth as a result.

Does Sugar Aid in Plant Growth?

The idea of using sugar to foster plant growth is nothing more than an urban legend. No scientific evidence has been found proving that adding sugar to a plant aids in its growth. At best, sugar (or a sugar-water solution) may end up being inadequate enough to encourage growth in some plants, while at worst, the mixture can harm—and potentially kill—plants.

What Can Sugar Do for Plants?

A study carried out by University of Pennsylvania biologists found that plants “use the level of sugar in their leaves to trigger the transition from juvenile to adult forms.” (Source: Penn Today) Plants have the ability to regulate their sugar levels in order to transition from young to adult development.

In other words, sugar can, in fact, aid in plant growth, but only through the plant’s own self-production of sugars; not through sugar additives.

In addition, some research suggests that adding sugar solutions to plants can help attract beneficial insects to protect plants from harmful insects. (Source: University of Nebraska-Lincoln) However, since the research is not definitive, it’s best to allow plants to produce sugar for this purpose naturally.

What are the Dangers of Adding Sugar to a Plant?

Sugar for Plants

For one, plants are not built to thrive from the sugar we typically buy at the grocery store. Why? The type of sugar plants produced from photosynthesis is glucose, which is a monosaccharide. The sugar that we typically eat is mostly polysaccharides, which are much more complex types of sugars that plants are not able to break down as easily.

In addition, it is impossible for the roots of a plant to take in sugar directly. If anything, the roots will be inhibited from taking in the water the plant needs.

Alternatively, if a dissolved sugar-water solution is added to the plant, it is very likely that the roots will reject it, especially if the plant is already healthy and photosynthesizing at a reasonable rate. 

A final danger to adding sugar to plants is that in abundance, it can attract micro-organisms that could threaten the health of the plant. Too much sugar in a plant could also lead to reverse osmosis, which can actually make it lose water and eventually wilt.

(Source: Ask.Extension)

When is it Okay to Add Sugar to a Plant?

Sugar water is typically only acceptable to give to cut flowers that are starting to wilt or other plant species that grow outside of the soil. The cut roots will absorb the sugar and allow flowers to live a little bit longer—and in many instances, look a little healthier, too.

For those who plan to try this, only roughly one teaspoon of sugar for every quart of water is needed—although this ratio may differ depending on the flower type and species.

It is not good to eat much honey, nor is it glorious to seek one’s own glory.

Proverbs 25:27

Alternatives to Sugar Treatment

If plants are still having difficulty achieving a healthy rate of photosynthesis and producing sugars, even with the best gardening practices in place, here are some alternative ways to help them:

Plant Food

Plant food is one of the go-to alternatives to sugar water; although it is more commonly used with indoor or house plants. Any type of organic plant food (Amazon Link) can help give plants a little boost. Make sure that the plant food selected is safe to use with the specific type of plants, and that the directions that come with the plant food are followed very carefully.

Gardeners who are raising an outdoor garden, organic fertilizer (Amazon Link) such as this works best as a plant food alternative.

While it is perfectly acceptable and safe to buy organic fertilizer for your plants, here at Do Not Disturb Gardening, we love to promote no till gardening by adding compost and mulch to the top of your soil at all times. With this method, over time, you should never have to buy any type of fertilizer! Please browse our site to learn more about these methods!

Club Soda

This method works best for young seedlings that do not yet have enough leaves to photosynthesize on their own.

Club soda (a.k.a. Sparkling water) is mineral water that is infused with carbon dioxide bubbles. The idea is that by adding the carbon dioxide water to the seedling, it can absorb the gas faster for photosynthesis and grow more quickly as a result. In addition, club soda usually contains minerals such as calcium, magnesium, iron, potassium, and other trace minerals. This is highly beneficial for plants living in soil with nutrient deficiencies.

Gardeners do not need to purchase any specific type of club soda for this method to work; any cheap brand will do! However, keep in mind that the more carbonated the club soda is, the better it is for the plant.

Gardeners only need to water seedlings with the club soda once a week.

Plastic Wrap

Gardeners with younger plants that are experiencing carbon dioxide deficiencies could try a plastic wrap application. Simply drape a layer of plastic cling wrap over the top of the plants to help trap carbon dioxide gases near their leaves.

However, keep in mind the plastic is not meant to be held over the plants for too long—only until the photosynthesis process is able to take place (noticeably after bubbles have stopped forming).

Talking to the Plant

It may seem silly, but some truth is behind plants benefiting from their owners talking to them! The carbon dioxide that is breathed out from one’s lungs as one talks to the plants can help plants absorb more of it in a short period of time. In fact, just a five-minute conversation is enough to provide them with enough carbon dioxide equivalent to one liter of club soda.

(Source: MIGardener)

Reasons Plants Have Trouble Growing

Left alone, most plants are able to balance photosynthesis, respiration, and transpiration processes very well. However, if there is an unbalance, the plant may have trouble growing.

Respiration > Photosynthesis

For example, if the respiration process occurs much more quickly than photosynthesis, the plant will not be able to produce enough energy to grow; in these cases, growth could slow down or stop.

Photosynthesis > Respiration

In addition, if the respiration process is too slow and is unable to break down the oils, proteins, or sugars produced from photosynthesis, the photosynthesis process will either slow down or stop in order for it to catch up. After a long period of time, growth will begin to slow down as well.

Transpiration > Photosynthesis

If plants end up losing too much water, usually due to hot or dry weather conditions, their stomata will close when transpiration is at its peak to avoid losing more water. However, when the stomata close, carbon dioxide is not able to enter. In other words, if a plant’s stomata are closed for too long, it will not be able to collect enough carbon dioxide needed for photosynthesis.

(Source: Oregon State University)

Lack of Carbon Dioxide, Sunlight or Water

Another reason plants may have difficulty growing is because they lack the essentials for photosynthesis: carbon dioxide, sunlight and water. Without these critical properties, a plant will be unable to photosynthesize, and if it is missing one of these three things for too long, it will unfortunately die.

Lack of Other Key Nutrients

A plant may face growth inhibition if it lacks any of its 17 essential nutrients, especially carbon, hydrogen, oxygen, nitrogen, phosphorus and potassium.

Environmental Factors

If a plant is under stress due to insufficient quantities of light, water, or air, or extreme temperatures, it may develop a nutrient deficiency.

Light

As mentioned above, light is essential for plant growth, as it encourages the process of photosynthesis in plants to create their own food. Three dimensions of light should be considered when it comes to its effects on plant growth: intensity, duration, and quality.

  • Intensity – The intensity of light influences how a plant manufactures its food, in addition to its stem length, leaf color, and flowering. The light intensity can be changed based on how near the light source a plant is. Plants facing the south usually receive the highest light intensity, while northern-facing plants receive the lowest. Naturally, a plant facing north is less likely to grow as fast as a plant facing south.
  • Duration – The length of time a plant is exposed to light also influences its growth; if a plant only receives low-intensity light, the difference can be made by increasing the duration of time the plant is exposed to it. Longer hours of light allow the plant to create enough food to survive and grow; although, be careful not to expose plants to direct sunlight no more than 16 hours if it is indoors.
  • Quality – Quality refers to the color or wavelength of light. Blue and red wavelengths usually have the most significant impact on plant growth because they are the two wavelengths plants easily absorb. Blue light is responsible for leaf growth, while red light—in combination with blue light—encourages flowering. Gardeners who plan on using supplemental growing lights must make sure they contain blue and red light.

(Source: University of Arkansas)

To increase the amount of light a ground-based plant is exposed to, try surrounding it with reflective materials, a white background, or use supplemental fluorescent, cool lights. To decrease the amount of light, hang a cheesecloth or woven shade cloth above the plant.

Water

Overwatering and underwatering can account for many plant losses. Too much water and plant roots could suffocate, while too little water can end up dehydrating the plant and cause it to wilt. Different plants require different amounts of water, so it is important to research the specific plant variety to ensure the plant is receiving the proper amount of water it needs. The type of soil used for a plant can also influence the amount of water required.

If a gardener is still unsure whether a plant is receiving enough water, it is recommended to stick an index finger about two inches into the soil around it. If the soil feels damp, enough water is present. If it is dry, the plant is likely in need of more water.

If a finger is unable to penetrate through the soil entirely, the soil may not be porous enough.

For more helpful information on watering your garden, check out our article When Should You Water Your Vegetable Garden?

Air

It is essential that a plant’s roots have access to air. If the soil is not porous enough, the plant could suffocate after being watered.

Ventilation is especially important for indoor plants since they are exposed to air from air conditioning and heating units. Flowering plants are especially sensitive to drafts and heat. For that reason, make sure that these plants are not located near air vents that could inhibit their growth.

Temperature

As mentioned previously, most plants undergo the highest rate of photosynthesis between 65 and 85 degrees Fahrenheit. Outside of this range, the process may slow down, which could slow the growth of plants.

During extremely cold temperatures, it is crucial to make sure that plants have plenty of mulch or compost to help insulate them. During hot temperatures, plants should be watered more frequently, so they do not dry out.

(Source: Oregon State University & University of Arkansas)

Essentials for Healthy Plant Growth

Sunlight, water, carbon dioxide, and temperature are all factors that help a plant photosynthesize and regularly produce food for itself. However, other essentials are necessary for a plant to stay healthy and grow:

Nutrients

Scientifically speaking, plants require 17 elements for growth. These elements are often divided into three main groups:

  1. Macronutrients – Macronutrients are nutrients that plants can obtain from the air and water, and include carbon, hydrogen and oxygen. Macronutrients are vital elements that a plant needs to ensure the process of photosynthesis can occur.
  2. Soil-Derived Macronutrients – Soil-derived macronutrients include: nitrogen, phosphorus, potassium, sulfur, calcium and magnesium. Of these elements, nitrogen, phosphorus, and potassium are required in the largest amounts: nitrogen for healthy foliage, phosphorus for flower development, and potassium for root growth. (Source: University of Florida)
  3. Soil-Derived Micronutrients – Soil-derived micronutrients include: Boron, chlorine, copper, iron, manganese, molybdenum, nickel and zinc. Although plants require smaller amounts of these elements, even a slight deficiency can affect them as much as lacking a more critical element such as nitrogen.

Most soil-derived macro and micronutrients can be found in healthy, organic soil. Many gardeners often perform soil tests to determine which elements or nutrients are missing.  Then they know which supplements should be used to help the plants.*

For some helpful links for a few soil tests we have used from Amazon, check out our products page Best Soil Amendments – Soil Tests.

*Note: Some fertilizers can help provide the missing nutrients soil needs. When choosing a fertilizer, make sure that it contains nitrogen, phosphoric acid and potassium, as these three elements are critical for healthy plant growth. 

(Source: University of Idaho)

Organic Soil

Healthy soil is critical to a thriving plant because it naturally provides many of the things it needs to survive:

  • Anchorage – The root systems of plants typically extend downward or outward through the soil; the soil helps stabilize these roots.
  • Oxygen – The small spaces between soil particles provide oxygen to living cells on the plant that help them break down sugars and release energy the plant needs to grow.
  • Water – The same spaces in soil that contain oxygen can also hold water for the plant.
  • Insulation – Soil can help insulate plant rooms from large fluctuations in temperature; this is especially important during the hottest and coldest times of the year.
  • Nutrients – Soil is also a supplier of nutrients for the plant, and can hold the nutrients added through fertilizers. Most of the nutrients a plant needs can be found in organic soil.

The best thing gardeners can do for their plants is to plant them in organic, nutrient-rich, and well-draining soil. Healthy fertilizer and/or mulch and compost can also help foster healthy plants.

Here is a great foundational article we have written about having soil – How to Know if Your Soil is Healthy: 11 Simple Tests.

Space

Growing plants need plenty of room to spread out, especially if it is a variety with roots that extend more outward than downward. If an area is overcrowded with plants, the resources available could be limited. For example, one plant may end up blocking sunlight for a neighboring plant that is too close to it. 

It’s important to plan the layout of your vegetable garden to ensure adequate spacing. Check out this article we have written for more information – Planning the Layout of a Vegetable Garden: A Complete Guide.

Shelter

A plant requires shelter from harsh environmental conditions, such as high wind. It is also important to make sure the location of the plant is in an area that can receive sufficient sunlight; if it is an outdoor plant, make sure it is placed somewhere that gets a good amount of rain.

Healthy Plant Function

Besides photosynthesis, a healthy plant has two other essential functions that aid in growth and development: respiration and transpiration.

Respiration

Respiration is the process in which plants create energy from the food they produce. This process occurs when the sugars produced from photosynthesis combine with oxygen to produce cellular energy. This energy is used to promote growth and other routine cell functions in the plant.

Respiration can only take place when there are enough oxygen and glucose molecules to combine. To ensure there is plenty of oxygen, make sure that the plant is in well-draining soil. Soil that does not drain well is likely to keep too much water longer, which can suffocate plant roots.

(Source: University of California)

Transpiration

Transpiration is the process in which plants pull water from its roots and direct it throughout the plant. During this process, a leaf’s “guard cells shrink, its stomata open, and water is lost.” (Source: Oregon State University). After being delivered to the top of the plant, the water is released into the air as water vapor.

Transpiration happens most often during hot, dry or windy weather to keep the plant hydrated. The process is also necessary for a number of other reasons:

  • Transports minerals from the soil to the plant.
  • Cools the plant during evaporation.
  • Moves sugars and plant chemicals.
  • It maintains turgor pressure.

Conclusion

Plants are adept living organisms that know how to take care of themselves. Through the natural process of photosynthesis, plants are capable of producing their own food as they need it, without our help.

Although adding sugar to a plant will not help it grow, gardeners can certainly use other tips to help plants thrive. As long as plants are provided with the key necessities for survival, such as sunlight, water and air—in addition to an environment with healthy, organic soil packed with nutrients, they will continue to grow and flourish the way God intended.

Check out Our Favorite Products page to find everything you might need to help make your garden a success!




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Corey Leichty

Hi, I’m Corey and I love using gardening as a way to provide food for my family, learn life lessons alongside my wife, Andrea, and teach life lessons to my two sons. Do you have gardening questions? Not finding what you are looking for? Please feel free to Ask a Question (Click Here!) and I will get back with you as soon as I can!

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