Cannabis cultivation on the commercial scale is a booming 21st century industry with substantial economic impact and robust capital expenditures required for facility buildouts. A unique agricultural endeavor, cannabis is often grown indoors with tightly controlled environmental parameters that deliver more intense light, higher levels of carbon dioxide, and steady humidity and temperature. Measures that limit the introduction of outdoor air and hygiene practices, which eliminate potential vectors of contamination entering the grow (e.g., humans, tools, materials, plants, etc.), are typical for successful operations. Nonetheless, challenges are numerous for indoor cultivation, partially due to constant moisture from watering and feeding of the crop in a confined space. Air handling systems are crucial to filter outdoor air and circulate indoor air. Proper drainage of excess water and avoiding sources of stagnant water are also fundamental to keeping mold growth to a minimum. One of the most common failures of cannabis flower batches tested at the state regulatory level is the ‘total yeast and mold’ category, and therefore mitigation of mold point-sources is highly beneficial for minimizing batch failures due to mold above the action limit (a threshold set at 10,000 colony-forming units (CFU)/gram in many states).
Monitor Your Environment
A proactive approach of monitoring the facility for any ‘hot-spots’ of microbial growth can help avoid a downstream test ‘fail’ of processed flower batches. Air handling systems that deliver air to plant rooms and any device that utilizes water for cooling or humidifying should be screened for total yeast and mold levels periodically. Often, there are many sources of air cooling in a given room, and each should be tested individually to inform on any ‘hot-spots’ that should be more heavily targeted with cleaning protocols. The plants in closest proximity to a contaminated unit can theoretically be batched together to limit the prevalence of elevated microbial loads across an entire harvest. Plants in locations more distant from the contamination source may have substantially less impact.
The irrigation system for water and nutrient delivery to the crop will likely form biofilm over time, and these organisms can be partially aerosolized upon application to the plant base. Intensive between-harvest cleaning regimens for these systems is another strategy for keeping bacterial, yeast, and fungal loads minimized, especially in the flowering stage. Dehumidifiers can also harbor a plethora of microbes in the water collection tanks. Processes for cleaning all such water collection tanks should be in place and be monitored for efficacy.
Drainage systems that remove excess liquid from watering and feeding the plants will contain the runoff and all associated microbial ecology, and hence, it is vitally important that buildup of biofilm is limited by effective cleaning regimens. Pooling of runoff on trays, floors, drains, or other locations should be remedied as soon as possible to minimize microbial blooms.
Test Your Inputs, Know Your Sources
Cannabis in its final market form is commonly tested for microbial contamination, heavy metals, pesticides, and mycotoxins, as well as for residual solvents in extracted products. Interestingly, cannabis has a strong tendency to bioaccumulate compounds present in the water, and soil or other growing media, in its environment. Testing these inputs before their introduction to the crop is good practice to screen out any products containing off-label pesticides, heavy metal contamination, or extremely high concentrations of mycelium, mycotoxins, or soil bacteria that could contribute to downstream final product batch failures.
With the current state of supply chain uncertainty, manufacturers may have trouble maintaining the exact ingredients they used previously. It’s now especially important to test each new lot or at least test periodically. For example, if a peat moss vendor switches sources and the new harvest source has trace levels of cadmium, the cannabis flower may bioaccumulate this element over the months-long growth cycle, and then test over the limit during final 3rd-party laboratory analysis for market compliance. Furthermore, some materials sourced from overseas and used in post-harvest processing of cannabis can pose a risk of heavy metals introduction, and should be tested before use if they will be in physical contact with the finished product bound for market shelves.
Quarantine the Introduction of Clones
Introduction of foreign plants to the facility is always a risk. Plan for a physical quarantine-specific space for new plants entering the facility, completely isolated from all vegetative, flowering, and mother plant rooms. Upon entry or as soon as possible thereafter, test the immature plant tissue for the presence of powdery mildew, pests such as mites, infections including hop latent viroid, and other cannabis-specific plant pathogens that can decimate the crop. Juvenile plants can be released from quarantine after test results are shown to be negative.
Opportunities for mechanical transfer of pests from one plant to another should be closely scrutinized to avoid the spread of infection that may otherwise be confined to a single room. When using tools to prune or cut clones, it is imperative that the tool is clean before use on the next batch of plants. At the very least, clearly marked tools should be strictly dedicated to the mother plants and never allowed to be used elsewhere in the grow.
Mitigating Failure Risks – Identify Your Inputs and In-Process Critical Control Points
Across all inputs and processes, it’s important to identify and monitor the critical control points which could lead to downstream out-of-specification events such as testing batch failures or other problems with quality such as lowered potency.
Inputs including water, soil mix and other growth media, and nutrients are good targets for a monitoring regime since they have such a large potential to affect downstream qualities of the plant.
Nutrient reservoirs and feed lines can harbor microbial growth, therefore cleaning procedures and monitoring of regrowth to inform frequency of cleaning is good practice for keeping microbial loads in check.
Introducing new genetics or immature plant stock are potential vectors for transfer of disease to the grow. Appropriate quarantine processes should be adhered to without exception. Tools (pruning shears and other items used during the vegetative and flowering stages) should be segregated to specific stages of the grow, never comingled, and routinely sanitized after use.
