As the operations manager at Los Sueños Farms, the largest outdoor cannabis farm in the country, I was tasked with the challenge of finding a yeast and mold remediation treatment method that would ensure safe and healthy cannabis for all of our customers while complying with stringent regulations.
While outdoor cannabis is not inherently moldy, outdoor farms are vulnerable to changing weather conditions. Wind transports spores, which can cause mold. Each spore is a colony forming unit if plated at a lab, even if not germinated in the final product. In other words, perfectly good cannabis can easily fail microbial testing with the presence of benign spores.
If all of those landed on cannabis it would be enough to cause over 450 pounds of cannabis to fail testing, even if those spores remained ungerminated.
It should also be known that almost every food item purchased in a store goes through some type of remediation method to be considered safe for sale. Cannabis is finally becoming a legitimized industry and we will see regulations that make cannabis production look more like food production each year.
Regulations in Colorado (as well as Nevada and Canada) require cannabis to have a total yeast and mold count (TYMC) of ≤ 10,000 colony forming units per gram. We needed a TYMC treatment method that was safe, reliable, efficient and suitable for a large-scale operation. Our main problem was the presence of fungal spores, not living, growing mold.
Below is a short list of the pros and cons of each treatment method I compiled after two years of research:
Autoclave: This is the same technology used to sterilize tattoo needles and medical equipment. Autoclave uses heat and pressure to kill living things. While extremely effective, readily available and fiscally reasonable, this method is time-consuming and cannot treat large batches. It also utilizes moisture, which increases mold risk. The final product may experience decarboxylation and a change in color, taste and smell.
Dry Heat: Placing cannabis in dry heat is a very inexpensive method that is effective at reducing mold and yeast. However, it totally ruins product unless you plan to extract it.
Gamma Ray Radiation: By applying gamma ray radiation, microbial growth is reduced in plants without affecting potency. This is a very effective, fast and scalable method that doesn’t cause terpene loss or decarboxylation. However, it uses ionizing radiation that can create new chemical compounds not present before, some of which can be cancer-causing. The Department of Homeland Security will never allow U.S. cannabis farmers to use this method, as it relies on a radioactive isotope to create the gamma rays.
Gas Treatment: (Ozone, Propylene Oxide, Ethylene Oxide, Sulfur Dioxide) Treatment with gas is inexpensive, readily available and treats the entire product. Gas treatment is time consuming and must be handled carefully, as all of these gases are toxic to humans. Ozone is challenging to scale while PPO, EO and SO2 are very scalable. Gases require special facilities to apply and it’s important to note that gases such as PPO and EO are carcinogenic. These methods introduce chemicals to cannabis and can affect the end product by reducing terpenes, aroma and flavor.
Hydrogen Peroxide: Spraying cannabis plants with a hydrogen peroxide mixture can reduce yeast and mold. However, moisture is increased, which can cause otherwise benign spores to germinate. This method only treats the surface level of the plant and is not an effective remediation treatment. It also causes extreme oxidation, burning the cannabis and removing terpenes.
Microwave: This method is readily available for small-scale use and is non-chemical based and non-ionizing. However, it causes uneven heating, burning product, which is damaging to terpenes and greatly reduces quality. This method can also result in a loss of moisture. Microwave treatment is difficult to scale and is not optimal for large cultivators.
Radio Frequency: This method is organic, non-toxic, non-ionizing and non-chemical based. It is also scalable and effective; treatment time is very fast and it treats the entire product at once. There is no decarboxylation or potency loss with radio frequency treatment. Minimal moisture loss and terpene loss may result. This method has been proven by a decade of use in the food industry and will probably become the standard in large-scale treatment facilities.
Steam Treatment: Water vapor treatment is effective in other industries, scalable, organic and readily available. This method wets cannabis, introducing further mold risk, and only treats the product surface. It also uses heat, which can cause decarboxylation, and takes a long time to implement. This is not an effective method to reduce TYMC in cannabis, even though it works very well for other agricultural products
Extraction: Using supercritical gas such as butane, heptane, carbon dioxide or hexane in the cannabis extraction process is the only method of remediation approved by the Colorado Marijuana Enforcement Division and is guaranteed to kill almost everything. It’s also readily available and easy to access. However, this time-consuming method will change your final product into a concentrate instead of flower and usually constitutes a high profit loss.
UV Light: This is an inexpensive and readily available method that is limited in efficacy. UV light is only effective on certain organisms and does not work well for killing mold spores. It also only kills what the light is touching, unless ozone is captured from photolysis of oxygen near the UV lamp. It is time consuming and very difficult to scale.
After exhaustively testing and researching all treatment methods, we settled on radio frequency treatment as the best option. APEX, a radio frequency treatment machine created by Ziel, allowed us to treat 100 pounds of cannabis in an hour – a critical factor when harvesting 36,000 plants during the October harvest.
Regardless of whether your grow is indoor or in a greenhouse, mold is a factor that all cultivators must consider.
After weeks of careful tending, pruning and watering to encourage a strong harvest, all cultivators are looking to sell their crop for the highest market value. A high mold presence, measured through a total yeast and mold count (TYMC), can cause a change of plans by decreasing crop value. But it doesn’t have to.
There are simple steps that any cultivator can take that will greatly eliminate the risk of mold in a grow. Below are some basic best practices to incorporate into your operation to reduce contaminants and mold growth:
- Isolate dirty tasks. If you are cleaning pots, filling pots or scrubbing trimming scissors, keep these and other dirty tasks away from grow and process areas. Dirty tasks can contaminate the grow area and encourage mold growth. Set up a “dirty room” that does not share heating, ventilation and air conditioning with clean areas.
- Compartmentalize the grow space. Mold can launch spores at speeds up to 55 miles per hour up to eight feet away without any air current. For this reason, if mold growth begins, it can become a huge problem very quickly. Isolate or remove a problem as soon as it is discovered- better to toss a plant than to risk your crop.
- No drinks or food allowed. Any drinks or food, with the exception of water, are completely off limits in a grow space. If one of your employees drops a soda on the ground, the sugars in the soda provide food for mold and yeast to grow. You’d be surprised how much damage a capful of soda or the crust of a sandwich can do.
- Empty all trash daily. Limiting contaminants in turn limits the potential for issues. This is an easy way to keep your grow clean and sterile.
- Axe the brooms. While a broom may seem like the perfect way to clean the floor, it is one of the fastest ways to stir up dirt, dust, spores and contaminants, and spread them everywhere. Replace your brooms with hepa filter backpack vacuums, but be sure that they are always emptied outside at the end of the work day.
- No standing water or high humidity. Mold needs water to grow, therefore standing water or high humidity levels gives mold the sustenance to sporulate. Pests also proliferate with water. Remove standing water and keep the humidity level as low as possible without detriment to your plants.
- Require coveralls for all employees. Your employee may love his favorite jean jacket, but the odds are that it hasn’t been cleaned in months and is covered with mold spores. Clean clothing for your staff is a must. Provide coveralls that are washed at least once a week if not daily.
- Keep things clean. A clean and organized grow area will have a huge impact on mold growth. Clean pots with oxidate, mop floors with oxidate every week, keep the areas in front of air returns clean and clutter-free, and clean floor drains regularly. The entire grow and everything in it should be scrubbed top to bottom after each harvest.
- Keep it cool. Keep curing areas cool and storage areas cold where possible. The ideal temperature for a curing area is roughly 60 degrees and under 32 degrees for a storage area. Just like food, the lower the temperature, the better it keeps. High temperature increases all molecular and biological activity, which causes things to deteriorate faster than at cooler temperatures. However, curing temperature is a function of water activity more than anything.
- Be Careful With Beneficials. Beneficial insects certainly have their place in the grow environment. However, if you have a problem with mold on only a small percentage of plants, any insect can act as a carrier for spores and exacerbate the problem. By the same token, pests spread mold more effectively than beneficials because they produce rapidly, where beneficials die if there aren’t pests for them to eat. It is best to use beneficials early in the cycle and only when necessary.
Hazard analysis and critical control points (HACCP) is a robust management system that identifies and addresses any risk to safety throughout production. Originally designed for food safety through the entire supply chain, the risk assessment scheme can ensure extra steps are taken to prevent contamination.
The FDA as well as the Food Safety and Inspection Service currently require HACCP plans in a variety of food markets, including high-risk foods like poultry that are particularly susceptible to pathogenic contamination. As California and other states develop and implement regulations with rigorous safety requirements, cannabis cultivators, extractors and infused product manufacturers can look to HACCP for guidance on bolstering their quality controls. Wikipedia actually has a very helpful summary of the terms referenced and discussed here.
The HACCP system consists of six steps, the first of which being a hazard analysis. For Dr. Markus Roggen, vice president of extraction at Outco, a medical cannabis producer in Southern California, one of their hazard analyses takes place at the drying and curing stage. “When we get our flower from harvest, we have to think about the drying and curing process, where mold and bacteria can spoil our harvest,” says Dr. Roggen. “That is the hazard we have to deal with.” So for Dr. Roggen and his team, the hazard they identified is the potential for mold and bacteria growth during the drying and curing process.
The next step in the HACCP system is to identify a critical control point. “Correct drying of the flower will prevent any contamination from mold or bacteria, which is a control point identified,” says Dr. Roggen. “We also have to prevent contamination from the staff; it has to be the correct environment for the process.” That might include things like wearing gloves, protective clothing and hand washing. Once a control point is identified, the third step in the process is to develop a critical limit for those control points.
A critical limit for any given control point could be a maximum or minimum threshold before contamination is possible, reducing the hazard’s risk. “When we establish the critical limit, we know that water activity below 0.65 will prevent any mold growth so that is our critical limit, we have to reach that number,” says Dr. Roggen. The fourth step is monitoring critical control points. For food manufacturers and processors, they are required to identify how they monitor those control points in a written HACCP plan. For Dr. Roggen’s team, this means using a water activity meter. “If we establish the critical control point monitoring, water activity is taken throughout the drying process, as well as before and after the cure,” says Dr. Roggen. “As long as we get to that number quickly and stay below that number, we can control that point and prevent mold and bacteria growth.”
When monitoring is established and if the critical limit is ever exceeded, there needs to be a corrective action, which is the fifth step in a HACCP plan. In Dr. Roggen’s case, that would mean they need a corrective action ready for when water activity goes above 0.65. “If we don’t have the right water activity, we just continue drying, so this example is pretty simple,” says Dr. Roggen. “Normal harvest is 7 days drying, if it is not dry enough, we take longer to prevent mold or bacteria growth.”
The sixth step is establishing procedures to ensure the whole system works. In food safety, this often means requiring process validation. “We have to double check that our procedure and protocols work,” says Dr. Roggen. “Checking for water activity is only a passive way of testing it, so we send our material to an outside testing lab to check for mold or bacteria so that if our protocols don’t work, we can catch those problems in the data and correct them.” They introduced weekly meetings where the extraction and cultivation teams get together to discuss the processes. Dr. Roggen says those meetings have been one of the most effective tools in the entire system.
The final step in the process is to keep records. This can be as simple as keeping a written HACCP plan on hand, but should include keeping data logs and documenting procedures throughout production. For Dr. Roggen’s team, they log drying times, product weight and lab tests for every batch. Using all of those steps, Dr. Roggen and his team might continue to update their HACCP plans when they encounter a newly identified hazard. While this example is simplistic, the conceptual framework of a HACCP plan can help detect and solve much more complex problems. For another example, Dr. Roggen takes us into his extraction process.
Dr. Roggen’s team, on the extraction side of the business, uses a HACCP plan not just for preventing contamination, but for protecting worker safety as well. “We are always thinking about making the best product, but I have to look out for my team,” says Dr. Roggen. “The health risk to staff in extraction processes is absolutely a hazard.” They use carbon dioxide to extract oil, which carries a good deal of risks as well. “So when we look at our critical control points we need to regularly maintain and clean the extractor and we schedule for that,” says Dr. Roggen.
“My team needs respirators, protective clothing, eyewear and gloves to prevent contamination of material, but also to protect the worker from solvents, machine oil and CO2 in the room.” That health risk means they try and stay under legal limits set by the government, which is a critical limit of 3,000 ppm of carbon dioxide in the environment. “We monitor the CO2 levels with our instruments and that is particularly important whenever the extractor is opened.” Other than when it is being opened, Dr. Roggen, notes, the extractor stays locked, which is an important worker safety protocol.
The obvious corrective action for them is to have workers leave the room whenever carbon dioxide levels exceed that critical limit. “We just wait until the levels are back to normal and then continue operation,” says Dr. Roggen. “We updated our ventilation system, but if it still happens they leave the room.” They utilize a sort of double check here- the buddy system. “I took these rules from the chemistry lab; we always have two operators working on the machine on the same time, never anyone working alone.” That buddy check also requires they check each other for protective gear. “Just like in rock climbing or mountain biking, it is important to make sure your partner is safe.” He says they don’t keep records for employees wearing protective gear, but they do have an incident report system. “If any sort of incident takes place, we look at what happened, how could we have prevented it and what we could change,” says Dr. Roggen.
He says they have been utilizing some of these principles for a while; it just wasn’t until recently that they started thinking in terms of the HACCP conceptual framework. While some of those steps in the process seem obvious, and it is very likely that many cannabis processors already utilize them in their standard operating procedures and quality controls, utilizing the HACCP scheme can help provide structure and additional safeguards in production.
In the first part of this series, we introduced Dr. Hope Jones, who took her experience in tissue culture from NASA and brought it to the cannabis industry and C4 Laboratories. We discussed some of the essential concepts behind tissue culture and defined a few basic terms like micropropagation, totipotency, explants and cloning. Now let’s get into some of the issues with cloning from mother plants and the advantages that come with using tissue culture for propagating and cultivating cannabis.
Time & Resources
Taking cuttings from mother plants is arguably the most popular method of propagating cannabis plants. It is a process that requires significant real estate, resources and labor. “Moms can take up a great deal of space that is not contributing directly to production,” says Dr. Jones. “I know from experience that scaling up production and/or adding new strains to the production line requires significant time and resources to raise and maintain new healthy and productive mother plants.” Each mother plant produces a limited number of clones per harvest period and over the course of her life cycle.
By using tissue culture, a cultivator can generate an almost infinite number of clones from one plant cutting. With so many growers calculating their costs-per-square-foot, micropropagation is an effective tool to save space, labor and time, thus increasing profit margins. “Just to put it in perspective: Holly Scoggins’ book Plants From Test Tubes, cites a Day Lily cultivator who uses micropropagation to produce 1,000 plants in 30 square feet of shelf space each week,” says Dr. Jones. “Using conventional methods, one would need a half-acre to produce the same amount of plants.” Cultivators can produce a much greater number of plants-per-square-foot by using micropropagation effectively.
Early Health & Vigor
Most tissue culture methods use sterilized vessels that contain sugar-rich media to support growth of plantlets before they can photosynthesize on their own. “The media is prepped, poured into vessels, and placed in an autoclave (or pressure cooker) where it is subjected to high temps and pressure to achieve proper sterility.”
The sterile environment and rich growth media supplies plantlets with an abundance of everything they need. “When plantlets emerge from culture, they are pathogen-free, with a stockpile of food and nutrient reserves that support rapid growth and vigor, superior to conventional cuttings,” says Dr. Jones.
Stress & Disease
As any grower knows, mother plants can sometimes experience stress and disease. This might come in the form under or over-watering, heat stress, spider mites, whiteflies, mold and viruses. “Any stress or infection that a mother plant is subjected too can impact progeny health and productivity in a couple of ways,” says Dr. Jones.
For example, diseases like powdery mildew and tobacco mosaic virus are often systemic, meaning that pathogens have spread to almost every tissue in the plant. Once infected, it is impossible to completely eliminate pathogens from tissues. Therefore any cuttings made from a diseased mother plant, even if they look perfectly healthy, will also be infected and can eventually present disease symptoms like reduced productivity and/or plant death, according to Dr. Jones.
How does tissue culture get around this problem? Remember that explants (small tissue samples used as starting material) can be extracted from any part of the plant. Meristematic cells in shoot tips and leaves are the source of new plant growth. Dr. Jones explains that these cells, and the first set of primordial leaves are not connected directly to the vascular tissue, the plant’s transport system by which pathogens spread. Therefore, meristematic cells tend to be disease-free, whatever the condition of the mother. It takes a sharp blade, a dissecting microscope, and a lot of experience to learn, but as Dr. Jones explains, “harvesting explants from meristems is a routine micropropagation technique used by ‘Big Horticulture.’ One example is the strawberry. Viruses and pathogens are so prevalent that the strawberry industry must use meristematic culture to ensure pathogen free progeny.”
Now let’s talk about epigenetics. We know that plants don’t have the option of physically moving away from stress or predation. Instead, they have evolved sophisticated ways of changing their own biology to adapt to and/or protect themselves. “Consider what happens to a mom exposed to a pathogen. The infected plant will start expressing (turning on) genes and making proteins that contribute to pathogen resistance,” says Dr. Jones. “These changes to gene expression are partly regulated by epigenetic modifications, chemical changes to DNA that increase or decrease the likelihood a cell will express a particular gene, but that do not actually modify the gene itself. Like annotations to a piece of music, epigenetic modifications don’t change the notes but rather how loud or soft, quickly or slowly the notes are played.”
This is where it gets interesting. “Epigenetic modifications can be systemic and long lived. Plants infected by a pathogen or stressed by drought will present widespread epigenetic modifications to their DNA,” says Dr. Jones. “For an annual plant like cannabis, those modifications are relatively permanent. Thus a cutting from a mom having drought or pathogen adapted epigenetic programming will inherit that modified DNA and behave as if it were experiencing that stress, whether present or not.”
In the wild, this adaptability is critical for plant survival and reproduction, but to a grower, this is a less-than-ideal scenario. “The epigenetic modifications allowed the mother to tolerate the stress, which is great from the perspective of survival and fitness, but it comes at a cost. Some of the finite energy and resources that usually support plant growth and reproduction are instead channeled to stress response,” says Dr. Jones. This trade off results in reduction in overall plant yield and quality. “Those epigenetic changes result in a new phenotype for that mother,” says Dr. Jones. “All cuttings from her will reflect the new phenotype. This is one major mechanism underlying what many in the cannabis industry (incorrectly) call ‘genetic drift,’ or the loss of vigor over successive clonal generations.”
This is again where tissue culture can be such a game changer. The process of dedifferentiation, as explained in part 1 of this series, can rejuvenate a “tired” mother plant by inducing a kind of reboot– clearing accumulated epigenetic modifications that negatively impact progeny vigor and productivity. In the third part of this series, we will discuss the five stages of micropropagation, detailing the process of how you can grow plantlets in tissue culture. Stay tuned for more!
As the drought in California persists and quickly becomes the new hydrological norm, many within the state have embraced efforts to find ways and means to live within the drought forced water “budget.” Because of the importance of water conservation, the cannabis industry should embrace its socio-ecological responsibility and seize the opportunity to help shift the perception of cannabis cultivation into that of a sustainable, high-value agricultural crop that can be grown in an environmentally safe manner, while using water efficiently.
The intersection of Prop 64, MCRSA and the drought provides the cannabis industry with a unique opportunity to positively impact water conservation. Because legal cannabis cultivators are just now designing blueprints for grow sites, these cultivators are in a position to build infrastructure and systems specifically designed to achieve permanent, sustainable water conservation.
By embracing and championing water conservation, the cannabis industry will achieve two goals: being a collaborative player in the larger community working towards sustainable water use and enhancing the overall perception of the cannabis industry in the conscious of the general public. For an industry seeking legitimacy, there is no better way to put cannabis in the mainstream conscious than by embracing environmentally responsible philosophies. Here are a few measures the cannabis industry should embrace:
The current drought has generated a state-wide conversation about tracking and recording water usage. Some commentators believe California is suffering from a water data problem. Recently passed AB 1755 is a step by California to address that shortcoming by creating a technology platform to aggregate and share water data. Cannabis cultivators should get onboard with measuring water usage. One method is to install sensitive flow meters in each drip station to precisely measure water used during each grow cycle. First, this provides the cultivator with a precise data set. Precise data sets are extremely important, especially when trying to achieve the two-part-goal of conserving water and maximizing crop yield. Second, having precise data sets allows the cultivator to determine, from harvest-to-harvest, increasingly precise ratios of input (water) to output (flower). Most likely, this input:yield ratio is subject to diminishing returns at the margin; that is, adding additional water will not proportionately increase crop yield. For instance, 50 units of water could produce 50 units of crop, but 75 units of water might only produce 55 units of crop. By measuring the input (water), the cultivator is able to identify the precise threshold where diminishing returns set in and can therefore reduce the “diminishing returns” water usage, saving money and conserving water.
Building on water-usage data collection, cultivators can then collaborate with each other and with water agencies. By sharing data sets, cultivators can quickly develop ideal input:yield ratios, can better understand how water usage fluctuates within each discreet grow cycle and can develop methods such as deficit irrigation and real-time soil moisture measurements. This collective industry knowledge will help each individual cultivator to reduce water-usage. In collaborating with local water boards, the boards will better understand how much water is being used and conserved by the industry. Additionally, if the boards have a more precise understanding of the expected usage per season or per specific period in a grow cycle required by cultivators in their jurisdictions, those boards can better plan for the peaks and troughs in water demand. Besides data sharing, agencies and cultivators can collaborate in developing “fill stations” (offering free, non-potable recycled water for irrigation), or help fund development of direct potable water technologies and other recycled water technologies. Collaboration amongst growers and with water boards will lead to greater water conservation.
An ancillary benefit to water conservation behaviors is the reduction of energy consumption. It takes an immense amount of energy to pump and transport water to end-users, such as cultivators. Reducing water usage in turn reduces energy consumption, because less water used means less water transported and disposed of. This is one method for indoor cultivators to offset energy consumption. In addition to reducing energy usage by conserving water, cultivators can follow Irvine Ranch Water District’s example of implementing an energy storage system to reduce costs and ease energy demand during peak hours. Indoor cultivators should adopt the same basic structure and mechanics: install Tesla battery packs to store energy for use during peak hours (when electricity is more expensive) and recharge the batteries at night when demand is low (and electricity is cheaper).
This is an exciting time in California’s history, with the pending election of Prop 64, the passage of MCRSA, and the opportunities present in the water-energy nexus. The $6 billion cannabis industry has an incredible opportunity to have a far-reaching impact on water-conservation. By being an active collaborator conserving water, the cannabis industry can position itself as a trendsetter and private sector leader in sustainable and eco-conscious methods, technologies, and processes.
When newspapers and television run a cannabis story, it is frequently accompanied by photos or video of vast, cavernous warehouses filled with veritable oceans of plants. Photos used to illustrate stories in the New York Times and Denver Post serve to illustrate this point.
This type of facility design is sometimes referred to in the cannabis industry as a “perpetual harvest” model. This is because plants are harvested piecemeal – one row at a time, for example – with new plants ready to flower replacing the recently harvested ones. In this model, flowering plants of various ages occupy the same space and the room is never completely harvested and empty, hence the “perpetual” moniker. This is in contrast to more compartmentalized facility designs, in which flowering plants are segregated in smaller groups in various rooms, which are then harvested completely before the room is cleaned and new plants ready to flower replace the previous ones.
The perpetual harvest setup appears impressive and lends itself well to portraying the volume of production being achieved in large facilities. This is likely why I have seen such models, or similar ones, copied in other states. Prospective entrants to the industry have also approached my firm with such designs in mind for their cultivation facilities. However, we generally advise against the perpetual harvest facility model, as this type of design imposes serious difficulties upon operators. Problems arise primarily in the areas of pest and contamination mitigation, ability to properly observe pesticide use and worker safety guidelines, and inefficiencies in lighting and HVAC usage. The problems noted are linked to the perpetual harvest design and can be mitigated with increased compartmentalization. Before getting to my recommendations, however, lets run down the issues created by the perpetual harvest model.
Lighting and HVAC Inefficiencies
In many photos I see of perpetual harvest facilities, the ceilings are extremely high, as are the light fixtures in most cases. This is likely the result of one of the main perceived advantages of such spaces, which is that they require minimal construction prior to getting up and running. There are no walls to be put up or ceilings lowered, and the lack of compartmentalization makes running wires and ducting much easier.
However, whatever capital was saved in initial construction will likely be burned up by increased ongoing operational costs. High ceilings such as those in the above photos mean more cubic footage that climate control systems must cool or heat. Additionally, due to the great height of the light fixtures, plants are not getting the most bang for their buck, so to speak, compared to designs that allow lights to be lowered appropriately to provide optimal intensity and spectrum. Double-Ended High Pressure Sodium (DE HPS) lamps are probably the most common type of lighting in use for flowering by commercial cannabis cultivators today, and they are ideally situated about four feet above the canopy when running at full capacity.
For businesses aiming for a no-frills production model with minimal attention to the light management needs of individual cannabis cultivars (or strains, as they are commonly referred to), then this consideration may be moot. However, those operations attempting to produce the highest-quality flower and plant material know the value of proper light management, as well as the fact that some cultivars respond differently than others to intense light. Indeed, I have observed cultivars that produce more when light intensity was decreased, while others thrived under intense light that would have seriously damaged others. This makes the one-size-fits-all approach to light management I’ve seen in most perpetual harvest designs generally detrimental to the quality of the final product, in addition to using the same amount of energy, or more, to achieve that lower quality result.
Difficulties in Pest and Contamination Mitigation
Such a design makes it easy for a small pest incursion to become a full-blown infestation. Because plants about to be harvested are sharing space with plants just beginning their flowering process, this means that both current and future harvests will be affected, or even lost entirely if the pest problem is severe. Having plant groups of different ages share the same space is generally unadvisable. This is because older plants, particularly those close to harvest, are weaker and more susceptible to pests by virtue of the fact that their life cycles are nearing an end. On the other hand, a more compartmentalized facility design provides physical barriers that can contain mites and mildew spores to some extent, limiting the damage done by individual pest incursions.
One of the essential tasks in an indoor cultivation operation is sterilizing just-harvested spaces to ensure that the subsequent run gets off to a clean start. This task could conceivably be performed in a perpetual harvest model; say, for example, trays, trellis frames, and other equipment are scrubbed after a row has been cut down and removed for drying or processing. However, due to the fact that there are always other plants in the room, it seems impossible for any plant group to get an assuredly clean start, as other plants may be harboring bugs, mold spores, or viruses, despite not showing signs or symptoms. The presence of plants also eliminates the possibility of using cleaning agents such as bleach, which gives off harmful fumes, but is sometimes necessary to completely sterilize an area that might have previously experienced some amount of powdery mildew or botrytis.
In Part II of this series, I will discuss some problems with pesticide use and worker safety regulations as well as provide recommendations for compartmentalization in cultivation facilities. Stay tuned for Part II of A Case for Compartmentalization: Problems with “Perpetual Harvest” Models in Cultivation, coming out next week.