An organized workforce and proactive preparation can help indoor cannabis businesses successfully bring down their crop.
After months of managing plant health, driving yields and potency, and perfecting the finish, harvest is always a highly anticipated event. Harvest also is a critical time when small mistakes can generate big problems, and major miscalculations can swiftly spoil entire crops. This point in the production cycle tends to have higher-than-normal labor requirements, so growers should plan accordingly to ensure the harvest process is efficient and error-free.
Outdoor cultivation is a marathon marked by erratic weather, pest outbreaks and disease hurdles, but the long season also allows ample time to develop the harvest process and organize the necessary workforce.
In contrast, indoor cultivation cycles crops much faster, and many facilities run on bi-weekly or weekly harvest schedules depending on scale and room orientation. Quality control is critical to success in any harvest situation, but harvesting indoor plants, especially with tight turnarounds, means standard operating procedures (SOPs) must be especially well-designed and efficient.
A grow room of mixed cultivars may present the opportunity to harvest over a period of time; however, most growers are trying to minimize the amount of time bench space is left unoccupied, which translates to pulling down a whole room at once. For a few hundred plants, this may not seem like a big project. But once your operation’s plant count hits the thousands, extra hands and a well-orchestrated plan are vital.
The following tips will aid indoor growers in executing a flawless harvest.
At Galenas, we remove 30% to 40% of low-trichome (fan) leaves no more than four to five days before harvest to streamline the harvest process while still allowing plants to build yield in the final week. We strip them all the way down one to two days prior to harvest to eliminate the need for defoliation post-harvest. It is important to reduce watering as you remove leaves, since plants will have less surface area for transpiration. Defoliating makes removing whole plants easier, allows for tighter spacing on racks, and improves airflow, thereby lessening the chance of contamination from mold and bacterial contaminants during the drying process.
Another way to get a jump-start on harvest is to cut out trellises in advance. If the outer edge of the trellis is left intact, you can often remove the inner grids one to two days prior to harvest for speedier removal on harvest day while still supporting plants. Another strategy is to have a team stagger-start their shift a few hours earlier the day of harvest to remove the trellis ahead of the team that will be cutting down plants.
Regardless of your preferred strategy, be sure to prepare tools and surfaces to maintain productivity and cleanliness. After keeping rooms meticulously clean throughout the growth cycle, the last thing anyone wants is to fail testing from a contaminated surface during harvest. Make sure your team has washed benches, floors, and walls because, despite best efforts, flowers may brush over them. Also, sanitize harvest bins, racks, hooks, and scales to avoid cross-contamination. Have the appropriate tools on hand—for example, scissors for trellises and loppers for cutting thick plant stems—and keep the tools sharpened and clean.
Employees should already be wearing clean clothes or scrubs, masks, hairnets, beard covers, and arm covers while working in the flower rooms, but making sure that everyone is safely covered is essential during harvest. Many microbial failures come from human contact, particularly during harvest and post-harvest activities. Reusable gloves, masks and arm covers can be loaded with contaminants, which makes disposable items a better option. Frequent glove changes are important, especially while entering and exiting flower rooms for breaks or changing tasks.
Research shows that up to three weeks before harvest, withholding irrigation while decreasing humidity levels may increase resin content in plants, and drier conditions hinder mold growth. Although more studies are needed, certain medicinal and aromatic plant (MAP) species have shown positive correlations between drought stress and enhanced secondary metabolite production. In addition, a 2019 study published in HortScience found that major cannabinoid production increased with a period of drought stress in the finishing phase of certain cannabis cultivars.1 (For more tips on increasing secondary metabolites in cannabis cultivars, visit bit.ly/cbt-increasing-metabolites.)
Limited irrigation in the final weeks of flowering can potentially optimize chemical content while also relieving dehumidification load, as plants that drink less emit less water vapor into the room. An added benefit of limited watering with most mediums is easier removal of lighter pots. However, whenever drought-stressing plants, remember the inherent risk of crop loss, diminished yield, or stressing plants to the point where pathogens or pests spread more readily.
A 2020 study published in Acta Physiologiae Plantarum states: “Drought is receiving rising attention in the literature because of the effect of climate change and all its ecological consequences, but it is equally crucial in the optimization of secondary metabolite production/cultivation techniques of medicinal and aromatic plant (MAP) species. Both in nature and in experimental designs, drought stress highly differs in its timing, length of time and severity; furthermore, test species/genotypes are never the same.”2
The same study continues: “Probably a degree of drought stress exists in which a desired essential oil accumulation or even an altered essential oil composition is achievable. Trials on endless variations of factors in a complex net of interactions (species/genotype/water deficit treatments/other stress and environmental effects) will always have a limited applicability without deep understanding [of] how the different water supply affects volatile production. Therefore, more research is required to reveal the molecular and biochemical mechanisms that allow for fine-tuning in cultivation.”
Regardless, reducing irrigation in the final stretch before harvest can not only mean lesser humidity loads and more efficient dehumidification, but also kickstart the drying process in plants. With tight turnarounds, a shorter time in the dry room can be critical when another room comes down and a new crop needs to move in.
Keep in mind that harvest is a very risky time for contamination. In a March 2022 review published in Molecules, authors reviewed post-harvest handling methods to determine best practices for timing, technology and preservation.3 The article states: “Cannabis can ... be contaminated during the harvest and post-harvest processing, exposing the medicinal plant to dangerous mycotoxins .... Most microbial contamination occurs during the harvesting. Storing the product with poor drying conditions under high humid[ity] encourage[s] the formation of microbial spores and harmful microbial toxins such as aflatoxin, as well as powdery mildew and botrytis, which is a cause of deterioration of medicinal Cannabis.”
The same review continues: “Drying and storage under uncontrolled conditions like moist and humid conditions can lead to fungal infections. Some mycotoxins like aflatoxins and ochratoxins require oxygen to grow. Therefore, eliminating or reducing the oxygen can retard the fungal growth during storage. As well as poor drying and storing under humid conditions, this can promote microbial growth and toxins like aflatoxin and mycotoxin-producing strains of Aspergillus, as well as powdery mildew, Botrytis, Cladosporium cladosporioides, Alternaria alternat[a], Verticillium, Salmonella, Enterobacter, Streptococcus & Klebsiella.”
Dry room environmental parameters should be dialed in well in advance of plants moving in, and airflow, temperature and humidity setpoints must be optimal. Individual rooms may differ, but we at Galenas find 55 to 60 degrees F and 55% to 60% humidity work well for reducing contamination risk. Some cultivators prefer to dehumidify more during the first few days before allowing humidity to rise after initial plant moisture is removed.
Cultivators should check moisture levels daily at various points in the dry room with moisture meters to analyze progress. If the room cannot be homogenized, plant rotation may be necessary. Personnel should adhere to strict standards regarding personal protective equipment (PPE) in the dry room, and minimal entry should be observed to reduce contamination points and maintain climate control. Inspect plants regularly for signs of problems, including mold growth, and have an action plan ready to address any issues.
With a trained workforce and proper preparation, every harvest can be a victory. Developing solid SOPs and adhering to them strictly will afford growers the opportunity for repeatable success and a strong finish.
Christine DeJesus is the director of cultivation at Galenas in Akron, Ohio.
1 Caplan, Deron & Dixon, Mike & Zheng, Youbin. (2019). Increasing Inflorescence Dry Weight and Cannabinoid Content in Medical Cannabis Using Controlled Drought Stress. HortScience. 54. 964-969. 10.21273/HORTSCI13510-18.
2 Szabó, K., Zubay, P. & Németh-Zámboriné, É. What shapes our knowledge of the relationship between water deficiency stress and plant volatiles?. Acta Physiol Plant 42, 130 (2020). https://doi.org/10.1007/s11738-020-03120-1
3 Al Ubeed HMS, Wills RBH, Chandrapala J. Post-Harvest Operations to Generate High-Quality Medicinal Cannabis Products: A Systemic Review. Molecules. 2022 Mar 6;27(5):1719. doi: 10.3390/molecules27051719. PMID: 35268820; PMCID: PMC8911901.
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