A recent article published in Ohioline summarizes how the growth of state-bounded recreational and medical marijuana markets may impact the hemp industry in states like Ohio. In that article, federal and state regulations are put in perspective, followed by a review of developments in consumer behavior and responses from leading producers in states with recreational status. Even though marijuana continues to be illegal at the federal level due to its high concentration of tetrahydrocannabinols (THC and related controlled substances), the sum of retail sales of cannabis-derived products is expected to reach $23 billion by 2025 (Somani 2019), which is nearly half the domestic market for all fresh vegetables combined (Mintel Group 2021). The article concludes with important marketing considerations that potential Ohio hemp growers should focus on to avoid expensive transaction problems.
This article presents the latest developments in techniques and practices that cannabis producers have invested in to meet the growing demand. In many ways, hemp and marijuana are forefront crops that are helping to develop drying and curing techniques, new alternatives of biocontrol, cultivar-specific fertilization programs, refined nursery practices, and breeding efforts that combine sensitive biotic and abiotic factors. This article complements the previous fact sheet by focusing on the latest aspects of cannabis production, rather than cannabis regulations and marketing.
The following sections are organized by the production stages of cannabis. The sections review the latest research findings in hemp and report growers’ conference discussions about marijuana production in states where cannabis is legal. Research findings and successful practices adopted by growers are jointly reported when available to better represent the industry’s knowledge frontier.
Appropriate cultivar selection has become easier for cannabis growers as breeders master photoperiodism and incorporate abiotic and biotic characteristics in their programs. Before anything else, interested growers should know that, in general, cannabis is a short-day plant. Its vegetative stage is maintained if the plants are exposed to full light spectrum for 14 hours or more daily. Short-day plants initiate flowering as daylight hours decrease due to a change of seasons or a reduction of supplemental lighting in greenhouses. This same phenomenon occurs with poinsettia and garden mums, two broadly known ornamental plants.
The advance in the cannabis industry is a result of leading breeders quantifying photoperiodism for several commercial cultivars and recommending those cultivars according to:
- the geo-position of the farm.
- the local climate’s probability of frost.
- the expected bioaccumulation of cannabinoids.
These three characteristics should guide growers as they may dictate the success or failure of the enterprise. Open field hemp growers in Ohio should consider cultivars that fit in the local conditions and reach flower maturity before total THC concentration goes beyond 0.3%. For obvious reasons, high tunnel and greenhouse operations face lower constraints. Frost may not be an issue and supplemental light can be employed.
Photoperiod, frost, and total THC concentration are of little concern for well-equipped greenhouse operations located in states where adult-use marijuana is not prohibited. Nevertheless, Ohio hemp growers should obtain clear information about these interrelated characteristics (i.e., cultivar-specific photoperiodic response, susceptibility to frost and other local climate conditions, and expected accumulation of total THC overtime) and examine cultivar options while considering the type of infrastructure available for production. Requesting this information and other sensitive data from prospective seed/transplant sellers is important to the overall success of any cannabis production effort.
Hemp programs overseen by state-level agencies also release periodic reports to advise growers against certain cultivars that have a propensity to concentrate total THC above the 0.3% allowed threshold. In Ohio, cultivars with a natural propensity to bioaccumulate THC are not prohibited as they are in other states, but growers are invited to consider alternatives that tend to meet regulation requirements.
Propagation and Nursery Techniques
Genetic purity and access to feminized seeds have also been a major concern for growers dedicated to the production of smokable flower and metabolite extracts. These two market segments represent approximately 70% of the cannabis market. Growers focus on genetic purity and feminized seeds because cannabis is a dioecious plant with male and female flowers occurring on separate plants. The female flower presents the desirable characteristics for commercialization and processing, while the male flower does not. In addition, cross pollination decreases female flower quality and reduces concentration of target metabolites such as cannabidiol (CBD) and terpenoids. To circumvent this challenge and avoid expensive operational costs associated with culling male plants in the greenhouse or open field, growers obtain feminized seeds or vegetatively propagated transplants that are certain to produce female flowers in the reproductive stage.
Seed suppliers have for some time attempted to communicate value with growers by stating that their seeds will generate female plants with 99% confidence. However, the lack of a reliable seed certification and the inability of suppliers to replace undesirable plants have led growers to prefer vegetatively propagated transplants instead. Most transplants are produced using stem cuttings excised from mother (female) stock plants, which makes them clones, naturally guaranteeing their genetic properties. Other transplants are produced using tissue culture techniques, leading to high quality young plants that are frequently sold at higher price points. It is worth highlighting that some state agencies do require registration and certification from cannabis seed and transplant suppliers, but these accreditations tend to focus on traits other than sex.
A recent partnership between two competitors in cannabis genetics serves to illustrate the industry progress. The partners reported that trait selection will be coordinated internally between the firms, while results from the breeding efforts will be offered to growers only through transplants. From the agribusiness and production management perspective, the partnership of the breeding firms is fabulous. It not only proposes a feasible route to solve a major operational challenge experienced by growers, but also leverages synergies between the breeders while also differentiating their service from others in the market.
The strategic partnering of suppliers is a natural outgrowth of adapting to growers’ needs and recent research results. The latest findings indicate that rooting success and root system formation improve when propagators use rooting hormones, select stem cuttings of a minimal diameter, and maintain the container substrate at warm temperatures:
- Dipping the tip of cutting stems in a 0.2% indole-3-butyric (IBA) acid gel solution leads to statistically superior rooting success and root formation when compared to the use of an organic rooting product or no application of hormone (Caplan 2018).
- Stem cuttings with 2.3–3.2 mm diameter yield higher rooting success and root system vigor when compared to smaller diameter cuttings.
- Maintaining the container substrate temperature at a constant 82ºF for four weeks after sticking stem cuttings into the substrate leads to faster root development and higher root vigor.
Rooted cuttings develop well in a wide range of substrates, except coir-based mixes with high amounts of perlite (> 45% volume by volume – v/v) (Cockson, Barajas, and Whipker 2019b). Peat-based substrates mixed with up to 30% perlite (v/v) tend to perform better in controlled systems than coir-based substrates. Results also show that cannabis transplants can be successfully rooted using a wide variety of commercial media (Smith et al. 2021).
These findings complement other nursery practices that are commonly adopted by commercial growers and propagators. Stem cuttings are approximately 5-inches long with three to four nodes and at least three fully expanded leaves. The cuttings are usually stuck in germination trays with at least one vegetative node under the substrate. Trays are kept in a greenhouse propagation chamber for approximately two weeks. Relative humidity inside the chamber is maintained at 95% for the first five days (0–4 days after planting (DAP) a stem cutting in the soil), reduced to 80% in the next four days (5–8 DAP), and to 60% for 9–12 DAP. After twelve days of acclimatization, germination trays are brought out of the chamber and placed in greenhouse benches where supplemental long-day lighting is provided (if necessary) to maintain the plants’ vegetative stage. For the entire nursery period, the chamber and greenhouse temperature are maintained at 75ºF. Stem cuttings are ready for transplant 28 DAP in most cases.
When the adopted production system is a greenhouse, rooted cuttings are transplanted into medium-sized containers (1.5-gallon buckets). Transplants may go to open fields at that stage as well. Greenhouse or open field cannabis plants are kept vegetative for approximately 40 days. Flower initiation begins after that period and flowers are mature 55 days after. These estimated times may vary significantly depending on the cultivar. Growers should stress these technical details with suppliers and breeders before selecting a cultivar.
When it comes to fertilization programs for greenhouse or open-field systems, growers rely on general sufficient ranges for horticultural crops or empirical evidence from experienced growers. Although research-based fertilization programs are not fully developed, a recent study has used tissue analysis to examine toxicity and deficiency thresholds for essential nutrients (Cockson et al. 2019a). The article provides a comprehensive overview on how to identify nutrient deficiency in cannabis, including visual aids to assist with diagnosis and corrective measures. For the deficiency and toxicity experiments, the authors departed from a reference-sufficient range published in Bryson et al. (2014). Results from Kalinowski et al. (2020) sought to refine the rather general sufficient range by examining nutrient accumulation in thirteen commercially available cultivars bred for their production of CBD extracts in controlled-environment systems. Results from the latter study showed that the accumulation of macro and micronutrients is somewhat different across cultivars, which highlights the need to develop a stage-by-stage, cultivar-specific, nutrient program.
Considering that fertigation is a common practice among greenhouse and open field growers, general guidelines often refer to nutrient content in parts-per-million (ppm) of water-soluble nutrients. But the “one-size-fits-all” recommendation is not free of potential problems. When not supported by the existing literature, growers should always return to the basics, conduct soil analysis (especially for pH), and use technical reports prepared for specific growing conditions and operation types.
Insect Pests and Disease Control
There is a relatively short list of crop protection products available for cannabis growers when compared to other cultivated plants. As marijuana and hemp have been perceived by many as developing crops, the research and development programs of chemical companies have not addressed growers’ needs as fast as one would expect for a $14 billion industry. The amount of time and rigor in the process for registering active ingredients and formulations at the U.S. Environmental Protection Agency (EPA) combined with the illegal status of marijuana at the federal level have resulted in poor technological support that growers can use to produce healthy crops. On the positive side, the EPA website maintains a list of pesticide products registered for use on hemp (EPA n.d.). While most states adopt the EPA list, state-level agencies are entitled to tighten EPA regulations and prohibit certain active ingredients. Growers should always consult their state’s regulatory agents to avoid complications. If the end goal is to produce medical marijuana, growers should also check whether the state-level program provides a list of approved pesticides. In Ohio, the list of approved pesticides available for growers engaged in the Medical Marijuana Control Program is maintained by the Ohio Department of Commerce (Ohio Department of Commerce n.d.).
The best support growers have found thus far to manage pests and diseases comes from preventative practices and the use of biopesticides. Pristine sanitation and rigorous scouting programs are key in production facilities to prevent occurrence of diseases with minimal to no protection technology available. Consultants and influential growers also recommend attention to the quality and hygiene of transplants, as stock cuttings may carry several types of pests and diseases. The procurement of transplants that have been propagated in vitro using tissue cultivation techniques mitigates the possibility of pests and diseases.
Sanitation and scouting programs become more relevant as the number of registered crop-protection products remains low and pathogens spread geographically. An example of unwelcomed spreads has been reported by Farinas and Peduto-Hand (2020) in a recent disease note. The researchers observed the presence of Golovinomyces spadiceus in Ohio for the first time in 2020. This discovery took place in a research greenhouse at The Ohio State University. The pathogenic fungus causes powdery mildew. Other pathogens are likely to spread nationally as cannabis-derived crops gain popularity. In addition to lighting control and protection against frost and severe storms, the limited number of crop-protection products that effectively manage diseases stands as a critical factor for the broad adoption of controlled environment agriculture (CEA) production systems.
Growers find better support when it comes to controlling pests. The biocontrol industry has done a fine job at testing and registering biopesticides for use in hemp crops. Out of 59 registered products at EPA, 58 are biopesticides that are highly effective at controlling certain thrips, whiteflies, aphids, armyworms, borers, caterpillars, and other pests. Independent entomologists and product developers have recommended the use of advanced techniques such as the use of trap crops or banker plants to assist in crop scouting programs to assess pest pressure and the survival of biological control agents. Information on crop scouting and biological control agent survival may be found on the websites of leading biopesticide companies.
Several post-harvest methods have been considered to improve productivity and reduce processing time in advanced operations. A recent study reviewed seven alternative drying methods commonly used in the food industry and discussed their advantages and disadvantages when it comes to the final concentration of desirable metabolites and energy consumption. Results suggest that depending on the target market, different methods may be more appropriate. Floral products must be dried at temperatures below 104ºF to avoid significant loss of terpenoids. If the goal is to produce CBD-based oils and extracts, the intermittent convective drying process is superior as it yielded the highest CBD concentrations in the experiment. The treatment with the highest CBD concentration was drying fresh flowers at 104ºF until 25% moisture content was reached, and then raising the temperature to 158ºF until 9% moisture content was reached. The total drying time was six hours (Challa 2020).
Advanced industry players dedicated to the production of floral products understand the negative effect of high temperatures on terpenoids concentration. While most terpenes vaporize at temperatures above 100ºF, important terpenoids responsible for unique aromas start vaporizing at 70ºF. For that reason and considering that buyers of floral products value unique flavors and aromas, processors are comfortable investing additional hours to dry freshly harvested flower buds. The common practice is to slow dry upside-down hanging buds in drying chambers at 62ºF with the drying room set at 55% relative humidity. This process may take somewhere between 5 to 7 days to reduce moisture content from 85% to 18%. Although it may seem like a long drying process, growers and processors located in states with recreational legal status report that terpenoids retention is high using these chamber parameters. Following the drying process, flower buds are removed from the chamber and placed in open containers in a conventional room with the temperature set at 70ºF for curing. The curing process takes 4–5 days and the final moisture content is between 15% and 13%.
In addition to paying close attention to regulations and market dynamics, existing and potential cannabis growers should scrutinize production aspects before investing effort and scarce resources. This article highlights the need to:
- adopt suitable cultivars to specific growing conditions.
- use refined nursery practices.
- prepare a fertilization and crop protection program ahead of time.
- select appropriate drying and curing processes.
These critical aspects of cannabis production should be continuously reviewed to enhance the chances of creating and maintaining successful enterprises.
Bryson, Gretchen M., Harry A. Mills, David N. Sasseville, J. Benton Jones, Jr., Allen V. Barker. 2014. Plant analysis handbook III: a guide to sampling, preparation, analysis, interpretation and use of results of agronomic and horticultural crop plant tissue. Athens, Georgia: Micro-Macro Publishing, Inc.
Caplan, Deron Michael. 2018, “Propagation and Root Zone Management for Controlled Environment Cannabis Production”. Ph.D. dissertation, School of Environmental Sciences, University of Guelph. https://www.researchgate.net/publication/327449941_Propagation_and_Root_Zone_Management_for_Controlled_Environment_Cannabis_Production.
Challa, Sai Kiran. 2020, “Drying Kinetics and the Effects of Drying Methods on Quality (CBD, Terpenes and Color) of Hemp (Cannabis sativa L.) Buds.” M.S. Thesis. Halifax, Nova Scotia, Dalhousie University. https://dalspace.library.dal.ca/bitstream/handle/10222/80480/Challa-Saikiran-MSc-Agri-March-2020.pdf?sequence=1&isAllowed=y.
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Kalinowski, Jennifer, Keith Edmisten, Jeanine Davis, Michelle McGinnis, Kristin Hicks, Paul Cockson, Patrick Veazie, and Brian E. Whipker. 2020. “Augmenting Nutrient Acquisition Ranges of Greenhouse Grown CBD (Cannabidiol) Hemp (Cannabis sativa) Cultivars.” Horticulturae Volume 6, Issue 4: 98. https://doi.org/10.3390/horticulturae6040098.
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