Produced through photosynthesis, carbohydrates are a plant’s primary source of energy, and they play important functions in plant development. While cannabis plants synthesize carbs on their own, providing supplemental carbohydrates can save the plant energy, allowing it to divert that energy to other processes, including budding and flowering. In this blog post, we explain what carbohydrates are, the roles they play, and why growers may want to consider supplementing their plants with carbs.
What are carbohydrates?
Carbohydrates (CH2On) are organic compounds made of carbon, hydrogen and oxygen—hence the name, “carbo-” for carbon and “-hydrate,” for water. The n in the formula stands for the number of carbon atoms in the molecule.
Plant carbohydrates are either structural or non-structural. Structural carbohydrates form cell walls. Non-structural carbohydrates are stored for energy; this includes glucose, which is produced during photosynthesis.
Carbohydrates can be further classified into three subtypes:
- Monosaccharides: As the name implies, these are simple sugars with just one (mono) sugar unit (saccharide). Glucose, fructose and galactose are all monosaccharides. While glucose is the main product of photosynthesis, plants also produce a lot of fructose. As the sweetest carbohydrate, fructose attracts insects and animals, which help plants pollinate.
- Disaccharides: These carbohydrates contain two simple sugar molecules. Lactose, maltose and sucrose are examples of disaccharides.
- Polysaccharides: “Poly” means many, so it’s no surprise that these carbohydrates contain long chains of monosaccharides. Starch, glycogen, cellulose and chitin are all polysaccharides. Starch stores simpler carbohydrates, including glucose, in plants.
Carbohydrates can be linked with other compounds, such as proteins and lignins, to form plant cell walls. Starches and other carbohydrate-based compounds are abundant within cells. (Figure 1).
Figure 1. Plant carbohydrates present in cells and cell-wall structures. Note that ADF stands for acid detergent fiber, NDF for neutral detergent fiber and NDSF for neutral detergent-soluble fiber. Oligosaccharides refer to carbohydrates with two to ten sugar molecules. Image source: Hall, Mary Beth. 2002. “Working with Non-NDF Carbohydrates with Manure Evaluation and Environmental Considerations.” Accessed June 18, 2024. https://www.txanc.org/Proceedings/2002/Non-NDF-Carbohydrates.pdf
How carbohydrates provide energy
Carbohydrates fuel plant growth and development from the moment a seed is planted.
During germination, carbs, primarily in the form of starch, are stored in the seed and provide the energy the embryo needs to emerge from the seed and grow.
Once the plant develops into a seedling, it can begin producing its own carbohydrates through photosynthesis, converting the light it captures into glucose and other simple carbs. Chemically, this process is as follows: 6CO2 + 12H2O + light energy → C6H12O6 + 6O2.
During respiration, when plants “inhale” in oxygen and “exhale” carbon dioxide, carbohydrates are broken down to release energy. Glucose is converted into simpler compounds like pyruvate and further metabolized in the cellular mitochondria to produce adenosine triphosphate (ATP), the energy currency of all life. Chemically, this process is as follows: C6H12O6 + 6O2 → 6CO2 + 6H2O + energy (ATP).
Along with gene transcription, carbohydrates provide energy for the folding and transport of proteins, as well as cell adhesion, signaling and defense responses.
Role of carbohydrates in plant physiology
In addition to providing energy, plants also use carbs for other critical purposes, including:
- Stress tolerance: Carbohydrates help reduce stress in plants in several ways. Plants accumulate protective sugars and amino acids, and under drought stress accumulate soluble carbs like sugars and sugar alcohols (e.g., sucrose and mannitol) to adjust their osmotic potential. Also called osmotic adjustment, this is the plant’s ability to maintain water uptake and turgor pressure (i.e., sturdiness) when water is limited. Carbohydrates are also involved in plant responses to oxidative stress caused by environmental factors such as high light intensity or pollution. They do this by producing antioxidants like ascorbic acid (vitamin C) and glutathione, which help protect cells from damage.
- Structural support and integrity: Cellulose and hemicellulose are the primary carbohydrates that provide structural support and rigidity to plant cell walls, although hemicellulose is more flexible than cellulose and helps to bind cellulose microfibrils (fiber-like strands) together.
- Energy storage: In addition to starch, the primary energy-storing carbohydrate, plants store sucrose, a disaccharide composed of glucose and fructose.
- Communication and signaling: Plants use glycoproteins, which are protein molecules linked to carbohydrate chains, to regulate cell growth and respond to environmental stimuli. Carbs are also integral to certain phytohormones like abscisic acid (ABA), a crucial plant hormone involved in response to stress and growth regulation.
Benefits of carbohydrate supplementation
If plants can synthesize carbohydrates on their own, why should growers consider supplementing their cannabis plants with carbs?
First, it takes energy to make energy. If growers supply extra carbohydrates to plants, their crops need to devote less energy to manufacturing them, allowing them to direct that surplus energy to synthesizing amino acids and other secondary metabolites. More amino acids mean more proteins, which in turn mean more material for bigger, denser buds, while more secondary metabolites translate into heightened resin and terpene production.
Second, providing carbohydrates in the form of sugar can increase plant health and resilience. For instance, sugar can attract beneficial insects and help to sustain them. One study found that treating rice with a sugar solution reduced diseases by half.[1] Other studies on sugar-treated corn show increased stalk strength at harvest.[2] Extra carbs also help feed beneficial microbes in the root zone. Remember that beneficial bacteria and fungi carry out numerous vital functions, including breaking down dead organic debris and converting it to plant-available nutrients, fending off harmful microorganisms that can infect the roots and keeping the roots clean.
It’s also worth remembering that although carbohydrates are necessary throughout all the phases and stages of a plant’s life, and the amount of carbs they need fluctuates, carbohydrates are more influential during flowering, especially during the bud-fattening stage halfway through bloom. Supplementing carbohydrates at this time—right when plants need it most—keeps crops’ carb reserves topped off.
Plants can make enough carbohydrates to survive, but if you want to increase your odds of getting the biggest yields possible, ensure those reserves are always full.
Emerald Harvest Team
[1] Rees, Jenny. 2015. “Research on Sugar Application to Crops.” Accessed June 18, 2024. https://cropwatch.unl.edu/research-sugar-application-crops
[2] Rees, Jenny, Gary Zoubek, Keith Glewen, Tamra Jackson-Ziems, Casey Schleicher, and Todd Whitney. 2013. “On-Farm Research Results: Sugar Applications to Corn and Soybeans – UNL CropWatch, April 4, 2013.” Accessed June 18, 2024. https://cropwatch.unl.edu/farm-research-results-sugar-applications-corn-and-soybeans-unl-cropwatch-april-4-2013
