Understanding the Key Drivers of Cannabis Growth Essential To Optimizing ProductionOver the millennia, farmers have come to understand much of the science behind plant biology—the roles water, nutrients and sunlight each play in successful crop yields. Yet for all this knowledge, they’ve remained subject to the whims of nature; too much or too little rainfall, for instance, could spell disaster.
More recently, we’ve discovered the advantages of bringing operations indoors, where we can control these variables. By teaming our plant biology know-how with technology, we now can replicate—often even improve upon—the results of traditional field cultivation. This has certainly been the case with cannabis, which has a long history with indoor growing as a result of its legal status.
As cannabis continues its pivot toward widespread legalization, growers are searching for ways to optimize the quality, quantity, and efficiency of their yields in a hot yet increasingly competitive market. The latest precision-growing technologies offer a path, but to realize the full potential of their operations, it is critical that growers have a solid understanding of the basic processes driving the growth of plants.
The image is courtesy of AEssenseGrows
The following primer describes the three primary processes that drive plant growth and development. Understanding them, then developing a Grow Plan that properly balances the tradeoffs, is key to ensuring fast turnaround of large, high-quality yields. The three key processes are:
- Photosynthesis—the process of taking light energy and converting it to sugar energy
- Aerobic Respiration—the process of breaking down stored energy into useful biological energy
- Transpiration—the process that moves water from the roots up through the leaves of the plant and into the atmosphere as water vapor
Photosynthesis uses energy from light to create sugars used for growth. About 60 percent is used for growth, and the remaining 40 percent goes into plant maintenance. Plants receive water and minerals from the soil (or, in the case of aeroponics, the minerals come from a fine mist sprayed to the roots), and carbon dioxide from the air to produce carbohydrates and oxygen.
There are two types of reactions to photosynthesis: Light reaction and dark reaction, and they work together in a cyclical fashion.
The Light reaction requires light from the sun or supplemental lighting, like HPS, CMH, or LED light sources. Leaf pigments such as chlorophyll absorb the light, and the energy is converted into chemical energy in the form of ATP and NADPH, high-energy molecules and facilitators for enzyme processes.
The Dark reaction, also known as the Calvin cycle, doesn’t require light. It converts low-energy compounds, like carbon dioxide, into high-energy sugars using the ATP and NADPH high-energy molecules. Leftover ADP and NADPH are funneled back into the light reaction, recharging like a battery for more use in the dark reaction.
The enzyme Rubisco extracts carbon dioxide from the air to eventually make sugars and other high-energy compounds. It requires lots of nitrogen, so it’s essential that growers include plenty of nitrogen in their nutrient solution for the photosynthesis process. Nitrogen deficiencies can slow down photosynthesis and cause yellowing of leaves.
Now that we’ve seen how sugars are produced through photosynthesis, let’s see how plants utilize them through aerobic respiration.
Aerobic respiration is the dominant reaction in the root zone for fueling new root growth. Roots can’t perform photosynthesis, so they need all of their energy to be generated and delivered from the leaves above. Oxygen is essential for the root zone; plants need the oxygen to burn sugars and turn them into energy. It’s similar to humans—we breathe in oxygen and use that to burn sugars to create biological energy.
The image is courtesy of AessenseGrows.
Once the plant converts sugars to energy through aerobic respiration, the energy is put to a variety of uses. For instance, it is used in plant maintenance to maintain chemical and electrochemical gradients across different membranes. The gradients assist in uptaking different nutrients. Energy is also used to translocate sugars around the plant, and for plant growth and forming new molecules and cells.
Different molecules require differing amounts of energy inputs for their creation. For instance, Lignin—the hard substance that makes up the wood tissue in plants—requires more than cellulose, the substance that forms cell walls.
Transpiration is the driving force of water movement into, through and out of the plant. Water comes in through the roots, moves up through vascular tissue, then is evaporated out of the leaves through tiny openings in the leaves called stomata.
Stoma, the manner in which the plant produces the oxygen.
Transpiration plays an essential role in evaporative cooling. Leaves act like swamp coolers; they cool a surface as they evaporate water. This is essential under hot lights indoors or the hot sun outdoors.
It’s also critical for gas exchange. As the stomata open to release water vapor, carbon dioxide is allowed to enter. And it maintains turgor pressure. Healthy plants are 80 to 90 percent water, and when they’re full, they stand upright, and the leaves are flat. Without enough water pressure, leaves become flaccid and wilted. Finally, transpiration is key to mineral uptake. Water is the universal solvent, enabling nutrients in soil or a nutrient solution to move throughout a plant to build the plants building blocks.
Striking the right balance within these three processes can help ensure optimal growth and profits. Failing to do so can stunt yields.
Consider this: Respiration increases with temperature and can have a big effect on productivity. As temperature and available light increase photosynthetic output, that output eventually plateaus. As an example, if we keep increasing heat, the plants can burn more sugars for maintenance than they’re creating, and with this increase in respiration, there could then be less net photosynthetic product than there is for storage and growth. In this case, the plants are not producing as much sugars for growth as they’re burning for maintenance, so growth and development is then limited. So, to get maximum results, growers must ensure that the results of photosynthesis exceed the results of respiration for net carbohydrate assimilation.
There are a lot of balls to juggle; managing only some variables, like light or nutrients, likely won’t bring optimal growth. Rather, growers need to take a holistic approach in managing the production system, combining technology with plant biology to ensure fast-growing, high-quality yields.
A Deeper Dive
For a deeper dive, join Seth Swanson and Karl Kulik of AEssenseGrow for HIGH QUALITY PLANT PRODUCTION: INTRODUCTION TO PLANT GROWTH AND DEVELOPMENT.
About the authors:
|Karl Kulik is a plant scientist at AEssenseGrows who received his bachelor’s in plant biology at UC Davis. He has grown cannabis since 2008 and managed the cuttings department in a California medical cannabis dispensary.|
Seth is the Plant Cultivation and Research Manager at AEssenseGrows. He received his B.S. in Horticulture Science from Montana State University and his M.S. in Horticulture and Agronomy from UC Davis. His role with AEssenseGrows is to help grow on-site and on-farm research as well as assist with customer support and product development.