Table of Contents:
- How to Grow Cannabis 101: An Introduction to Cultivation
- Cannabis Greenhouse vs. Indoor Grow
- Minimizing Indoor Grow Costs
- How to Maximize Cannabis Yields
- Cannabis Greenhouse Construction Process
- Cannabis Cultivation Equipment
- Planning a Cannabis Cultivation Facility
- The Unique Challenges of Cannabis Cultivation
- VPD Dehumidification & Cannabis Cultivation
- Light and PAR
- Cannabis Irrigation
- Top 20 Cannabis Growing Questions – FAQ
- Glossary of Terms: Cannabis and Hemp Extraction
- Industry Resources
The Cannabis Lifecycle: The Perfect Balance of Air, Water, and Light
Cannabis has many names and valuable properties that have made it a crop grown around the world for millennia. From food to medicine, to recreation, and to fiber, cannabis (or “hemp” as it is also called) has followed human migration across the world. And now, its interaction with the human endocannabinoid system that produces valuable medicinal properties has raised its profile to become a high-value crop in a class of its own.
Today, one of the huge benefits of cannabis is its profitable potential along with a unique regulatory environment. Unlike other plants, cannabis can be pushed to increase its cannabinoid yield through human manipulation of air regulation, water, and light. This ability to increase yield relative to various environmental factors has allowed cannabis growers to push the boundaries of agricultural technology. Therefore, to cultivate cannabis successfully, you’ll need a keen understanding of the balance of light, air, and water, along with cannabis’ own unique characteristics, and also properly designed growing facilities.
When cultivating cannabis for the medical and recreational markets, our goal is to produce the most terpenes and cannabinoids that we possibly can. Both are found in abundance in the trichomes of female plants.
When female flowers receive pollen from male plants, they begin to produce cannabis seeds, which in turn reduces cannabinoid potency. This reduction in potency is why restricted access to male plants is a critical component of the cannabis cultivation framework; in many ways, we work against what cannabis naturally wants to do, which is to reproduce itself. It’s this state of ‘tension’ that creates valuable and potent cannabinoids.
Table of Contents:
This article covers the cannabis lifecycle and how to find the perfect balance of air, water, and light to ensure a successful crop:
The Cannabis Lifecycle
As an annual flowering plant, the cannabis plant’s life cycle is limited to one season and after harvest, the plant dies. This lifecycle can start in a couple of different ways, but typically the plant makes its way through a vegetative and flowering period before harvest. Commercial cultivators will propagate their plants typically using one of three techniques: seed, cuttings, or tissue culture.
1. Propagation from Seed
Starting a cannabis plant from seed is common, particularly for outdoor production. Well-stored cannabis seeds can be used years after their creation but come with a few notable constraints.
The first constraint is that seeds must be sorted between male and female to avoid potential pollination, and even then, crop walking is needed to identify potential male plants that may have made it through this initial screening.
The second hurdle is that propagating from seed can take additional time compared to a cutting, typically about two weeks longer. Cannabis seeds germinate rapidly, requiring only several days to produce a hypocotyl. During this germination period no light is required, but to avoid stretching of hypocotyl a low light level is recommended.
Typical temperatures for germination are 65F-75F with a relative humidity near 95%.
2. Propagation from Cuttings:
The most common way to propagate cannabis is through cuttings from a mother or vegetative plant. Mother plants are ideal specimens that are kept in a constant vegetative phase. Cuttings can be taken from the plant and rooted to form a clone of that plant. This process ensures a female plant with known traits.
A mother plant can produce 10 cuttings per square foot of canopy each week. Ideal cuttings are less than 6” long and have 2-3 leaves. It is common to grow cuttings for two weeks in a cloning machine, grow dome, or celled tray with a high humidity level and temperature of 75F-80F. A root zone that is too cold or low in oxygen will experience delays in root production which is the most critical part of this phase.
3. Propagation from Tissue Culture:
Another technique gaining popularity in the cannabis propagation sphere is tissue culture. Tissue culture is a form of cloning in which a piece of plant tissue is sterilized and placed into an agar petri dish. The specimen grows for at least a month in this jar and can then be transplanted into a more typical media for additional vegetative growth.
Care must be taken to not shock the delicate clone when it enters a new environment as it received minimal stress in its lab-like setting. Tissue culture avoids much of the disease transfer risk from mother plants to cuttings; at large scales, the labor involved is much less than growing mothers and taking cuttings from them.
|Propagating From||Seed||Cutting||Tissue Culture|
|KEY: 1 = best, 2 = medium, 3 = least|
The goal of the vegetative phase is to increase the size of the plant prior to flowering. What defines the vegetative phase is its photoperiod. Cannabis experiences photoperiodism in that as the number of daylight hours decreases, the plant transitions from a vegetative growth cycle to flowering (mimicking the yearly daylight cycle.) For the vegetative cycle, this photoperiod control takes shape in the form of an 18-hour light on and a 6-hour light off pattern. For flowering, the photoperiod is typically set at lights on for 12 hours and off for the other 12.
Cannabis can be grown in its vegetative phase nearly indefinitely as long as a proper photoperiod is kept. Mother plants have been known to last years, but this practice is not recommended due to depleting gains. For plants going to flower, their vegetative period typically spans 2-8 weeks after roots have been established. Vegetative plants should be spaced out in accordance with how long they will be in an 18-hour photoperiod.
Common techniques to increase yield include topping and pinching, which produce multiple main shoots and greater lateral growth. Temperatures during the vegetative stage should stay between 70F-85F, getting cooler at night, with RH levels of 60%-75%.
Transitioning to the flowering phase is a crucial step as it is here the cannabinoid-rich trichomes will be produced. A photoperiod of 12 hours of light and 12 hours of dark is induced to begin the flowering cycle.
Controlling this dark period is very important and all light leaks should be prevented, as interruptions to the dark period have been associated with hermaphroditism in female plants, causing the production of pollen sacs.
The flowering cycle typically takes 8-9 weeks before flowers have matured, reaching ideal cannabinoid and terpene levels. The concentration of oils is most prevalent in buds near the top of the canopy and reduces in potency closer to the base of the plant as well as in the leaves.
These lower potency sugar leaves and popcorn buds are ideal candidates for trim and extraction. To maximize the canopy, techniques like screen of green method and scrogging (SCROG) have been used to support the weight of the buds and create more colas using supports fashioned with netting, typically using multiple layers.
Another common technique during the flowering cycle is de-leafing or defoliation, which can be done once or twice prior to harvest. Removing leaves is meant to minimize transpiration and microclimates inside the canopy; microclimates should be avoided as they can lead to disease outbreaks.
An ideal temperature for flowering cannabis is 68F-80F with an RH of 50%-60%. The most important and precarious phase of the cannabis lifecycle is the final weeks of flowering. This is when transpiration is at its highest and microclimates can appear in the dense bud canopy, causing disease outbreaks.
A variety of cannabis gaining traction for its ability to defy photoperiod constraints is auto-flowering varieties. These auto-flowers mature separately from the photoperiod and are typically grown from seed outdoors. The two factors holding auto-flowering strains back when compared to traditional photoperiod strains are their cannabinoid and terpene profiles and a high level of variability of maturation time.
Upon harvest, cannabis plants are removed from the cultivation environment and transitioned to any number of steps depending on the desired final end-product.
In the case of an end-product like dried flowers, cannabis can be pretrimmed or the whole plant can be dried. The plant is dried over a period of 2 days to 2 weeks and loses approximately 80% of its mass. Cannabis that is dried slower is less harsh when smoked.
Typical temperatures for drying are 55F-65F with an RH of 55%-65%. The drying phase is usually followed by a curing phase to ensure homogenous moisture levels throughout the cannabis flower.
Growing cannabis is different from many other flowers, but at the end of the day, it still requires many of the same inputs any other photosynthesizing plant needs. Creating a balance of light, air, and water components is key to growing a successful crop. Growers can drive cannabis productivity by manipulating these factors to increase yield by improving each component in tandem with the others.
Cannabis Cultivation – A Balancing Act
“Cannabis loves light” is a familiar axiom in cannabis cultivation circles. Quite often, many will cite that adding 1% light equates to a 1% increase in yield. Research is beginning to show a potential linear correlation between light intensity and yield up to 1,800 umol/m2/s or nearly 80 DLI/m2 over a 12-hour period. This is an enormous amount of light, nearly 3x times the recommended level for tomatoes and 5x times that of lettuce. Cannabis’ ability to utilize such a high amount of light in the production of cannabinoids has brought a new perspective to driving the plant.
As cannabis photosynthesizes more light, it requires additional carbon dioxide and water. Due to the sugars made during photosynthesis, the plant grows faster and needs additional nutrients along with oxygen to undergo cellular respiration.
Providing too much light and not enough of these other elements may create more harm than good and this is why many facilities aim for 25-35DLI/m2 of light.
Supplementing light via grow lights can also prove quite expensive from a capital and operational cost perspective. In some cases, it may be more effective to build additional cultivation areas. When selecting a grow light, it is important to look at what type of light cannabis uses.
In the world of horticulture, light is often measured in terms of photosynthetically active radiation, or PAR. This range measures light in the ranges of 400-700 nanometers in wavelength, similar to how humans see light in the visible spectrum from 380-750 nanometers.
The PAR spectrum is used because plants primarily use light in this range during photosynthesis. However, even in the PAR spectrum, all light is not equal, as certain wavelengths induce photosynthesis and other reactions.
Blue light is at the lower end of the PAR spectrum and is associated with increased photosynthesis and inhibiting plant stretching. Blue light is often preferred during the early stages of plant growth. Green light is known for low photosynthesis output but does help humans and bugs in the environment perform more naturally. Red light has a high photosynthesis output and is essential for flowering.
Outside of the PAR spectrum is far red light which is not photosynthetic but can increase stretching, inhibit branching, shorten flowering period, and increase overall yield. On the other end of the spectrum is UV light which can increase stress amongst plants causing additional cannabinoid production in cannabis.
With increasing demand for photosynthesis, plants require additional water and nutrients. These nutrients can be provided in the grow media, through the irrigation water, or via foliar application. Nutrients are broken into categories of macro- and micronutrients based on the total quantity of the building block required.
In the root zone, the pH affects the solubility of certain nutrients which can impact the plant’s uptake of them.
Image credit to https://2fast4buds.com/news/what-is-pH-level-and-why-its-important-for-growing-cannabis
There is also the necessary management of the oxygen level in the root zone to ensure the plant can respire. Keeping the root zone environment in balance with regards to water, nutrient, and oxygen availability becomes more difficult with less room for error as light levels increase and the uptake rate increases.
What water that does not go to irrigation runoff is transpired from the plant or evaporated into the environment where it must be eventually removed.
Water can be removed from the environment through venting or dehumidification technologies. This is controlled by monitoring the relative humidity, RH, which is the percentage of water the air can hold at a given temperature before water begins condensing out of it. When the RH is too high, it can lead to disease outbreaks. As the RH decreases the plant will experience a greater water loss. In environmental control, RH works in tandem with temperature.
Air Balance and Plant Leaf Temperature
Controlling the temperature for plant growth can involve cooling or heating the environment, but ultimately the plant leaf temperature is the true indicator.
Generally, increasing the temperature improves plant growth until it becomes too hot, and then the plant overheats. This overheating occurs when the plant cannot keep itself cool, and it cools through the adiabatic process known as transpiration. Plants control their internal temperature though opening and closing their stomata and when they open it carbon dioxide, CO2, is up taken, and water vapor is released.
Increasing the concentration of CO2 increases the amount that the stomata take in when opening. This leads to the creation of more sugars and greater plant growth.
Ambient CO2 levels rest around 400ppm, but cannabis cultivators looking to deliver higher light levels should look to increase concentrations between 1,000-1,500ppm. To keep CO2 levels elevated, air exchanges must be limited, which can mean transpired water must be removed by means outside of venting.
The first step in driving cannabis to produce greater yields is to provide more light, but as photosynthesis increases, the rest of the inputs must follow suit in order to keep the plant healthy and strong. Without careful attention to water and environmental management, it all may be for naught and disease outbreaks could be right around the corner.
Achieving the Perfect Balance for Cannabis Cultivation
In summary, achieving the perfect balance of the three critical elements of light, air, and water may take years of perfecting your growing techniques. But once you have learned to master these three elements, you’re on your way to becoming a master cannabis cultivator.
To learn more, read the next article in this series: Greenhouse vs. Warehouse: Cannabis Cultivation: Indoor Grow or Greenhouse Sun Grown? How current Trends are Shaping the Industry.