Industrial Hemp Production (Part I): Cultivation and Management
The production of industrial hemp, grown for fiber, seed, and cannabidiol (CBD), has surged in recent years. More recently, the Agriculture Improvement Act of 2018 (2018 Farm Bill) authorized the production of hemp and removed hemp and hemp seeds from the Drug Enforcement Administration’s (DEA) schedule of Controlled Substances. However, producers continue to face challenges in production and marketing of products because of constantly morphing state and federal regulations, typically revolving around total tetrahydrocannabinol (THC) levels within the plant, that affect both how crops are grown as well as the ability to harvest, sell, and process those products. THC is the main psychoactive compound that gives marijuana users their “high.” While marijuana cultivars typically contain 3% to 15% THC by weight, hemp cultivars are bred to contain only trace amounts (less than or equal to 0.3%).
In addition to consumptive uses, alternative markets are also being explored. Hemp has been researched as a potential tool for phytoremediation and for potential biomass and energy production as both a biogas and solid fuel. Hemp fiber is being used for everything from plastic composites to car insulation. There have also been numerous studies on fiber quality, harvest times, flowering dates, and other basic production information. Therefore, it is important for growers to focus on what they want to cultivate most (fiber, grain, or flower), find the cultivars having the characteristics most desirable for that market, and understand production challenges and environmental constraints for their specific regions.
The purpose of this article, Part I, is to give a basic overview of the different types of industrial hemp crops as well as agronomic considerations when growing those crops. Part II of the series will focus on integrated pest management and potential impacts on wildlife resources. Several additional articles will follow within this series and will be used to explore various issues along the entire supply chain, including production and marketing. Readers are encouraged to research regulations for industrial hemp production within their respective states as well as contact federal, state, and local agencies for additional information specific to their region.
Many of the newest hemp cultivars have been bred specifically for the CBD market and purposefully have higher CBD to THC ratios. CBD, one of numerous known cannabinoids, is reported to have many health benefits. Tinctures, lotions, edibles, and numerous other products – including the first and only clinically formulated and FDA-approved drug on the market for epilepsy (Epidiolex) – are created from CBD extracted from hemp flowers. Because CBD is extracted from glandular trichomes in unpollinated female hemp flowers, production involves asexual propagation (cuttings, transplants, clones) of female plants or the use of “feminized” seed. Male plants and their pollen are undesirable in a CBD hemp crop.
Cannabigerol (CBG), a less-known cannabinoid, is considered a precursor to other cannabinoids and is currently gaining attention for possible use in pharmaceutical markets. Some health conditions for which CBG is being researched include inflammatory bowel disease, glaucoma, bladder problems, Huntington’s disease, colon cancer, and staph infections. Very little is known about the side effects of CBG oil or other forms of CBG, their long-term health effects, or interactions with other drugs. Therefore, more research is needed before widespread use can be expected.
Hemp fiber, in contrast to cultivars grown for CBD, is used to create fabric, rope, insulation, bioplastics, and similar products (Pal and Lucia 2019, Mitchell and Uchanski 2020). Cultivars grown for this purpose are comprised of “bast” fibers (used for textiles, papers, insulation, and construction materials) and “hurd” fibers (commonly used for animal bedding, pulping, and concrete products) (Salentijn et al. 2015, Michell and Uchanski 2020). Once harvested, hemp must undergo a process known as “retting”, which begins breaking the chemical bonds that hold these two types of fibers together (Kaiser et al. 2015). This can be accomplished by leaving cut stalks in the field several weeks until rot sets in and fibers separate, but not so long as to result in deterioration of fiber quality. The process, of course, will be largely affected by local environmental conditions. Water retting is a more expensive, but reliable alternative in which stems are submerged for several days (Kaiser et al. 2015).
Hemp seeds are used in human food products, health supplements, personal hygiene products, lubricants, paints, solvents, hempseed oil (as distinct from CBD oil), and other products. As a dietary supplement for humans it contains a highly desirable ratio of omega-3 and omega-6 fatty acids compared to many other potential sources and is relatively high in both oil and protein contents (Williams and Mundell 2018). Hemp grain can be used to produce a wide array of consumer products including raw hemp hearts, toasted hemp seed, hemp seed oil, hemp flour, and even hemp coffee (ibid.). Oftentimes, dual-purpose industrial hemp crops are grown in which grain is harvested first followed by the stems for fiber production.
Hemp seeds are combined/harvested when 70% of the seed is ripe (Kaiser et al. 2015). Harvesting grain past the optimal time generally results in lower quality seed, losses due to shattering, and possible bird damage. Seed should be dried to below 12% moisture for storage and from 8 to 10% for long-term storage.
In the world of industrial hemp production, the old axiom, “an ounce of prevention is worth a pound of cure”, certainly applies! Wind, hail, drought, pests, and other stressors can increase total THC levels in plants. If THC levels exceed the 0.3% threshold, producers are at risk of violating local, state, and federal laws and may be subject to fines and destruction of crops. Furthermore, there are currently no pesticides (insecticides, nematicides), herbicides, or fungicides labeled for use in industrial hemp crops in the U.S. This is true for both indoor and outdoor (field-scale) production systems (Williams and Mundell 2018). Therefore, good crop management and planning are essential to reduce those risks and improve the likelihood of a successful crop.
Different varieties of industrial hemp respond very differently depending on latitude and basic agronomic inputs (Williams and Mundell 2018). In order to improve both yields and quality, industrial hemp should be planted on well-drained soils with high fertility, rich in organic matter. Soil pH should be at or slightly below neutral. A standard grain drill using either conventional tillage or no-till can be used if planting from seed and some moisture is needed to germinate or weeds will take over. An ideal seeding depth is ¼-inch, and plants germinate best in a firm bed (Kaiser et al. 2015). Recommended fertilizer applications range from 50 – 150 lbs/acre of nitrogen depending on a variety of factors; additional research is required before scientifically-based fertilizer recommendations for hemp production can be made.
Spacing of plants, local environmental conditions, and crop type should be strongly considered prior to cultivation in order to reduce the risk of crop pests and disease. For CBD and/or seed oil production where branching and flowering is desirable, allowing for adequate air flow around the plant can reduce transmission of pests while reducing excessive moisture accumulation on leaves that might increase the chances for blights or spread of other fungi. Use of drip irrigation and appropriate plant spacing also reduces competition for water, sunlight and nutrients with neighboring plants. In contrast, hemp for fiber is planted in dense stands to promote taller height and discourage branching and flowering, thus maximizing fiber yields (Kaiser et al. 2015). Because of the challenges of registering hemp as an agricultural crop, the Environmental Protection Agency does not readily recognize pesticides (herbicides, insecticides, fungicides, nematicides, etc.) for hemp in the U.S, so growers must follow good cultural practices to reduce the impact of pests, especially weeds (see the next installment in this series: Part II – Integrated Pest Management).
Knowing flowering times is critical for the production of hemp for CBD. When being grown as transplants, flowering can be initiated with even the slightest amount of root restriction. Most hemp cultivars will flower when exposed to day lengths of fewer than approximately 14 hours. Though farmers may be tempted to plant hemp early in the spring after the risk of frost has passed (i.e., April or May), especially in more southerly regions, hemp may begin to flower before the plants have had a chance to undergo any vegetative growth. Similarly, if growers plant too late in the season (late July), plants may flower prematurely (Kaiser et al. 2015, University of Georgia 2020). Therefore, planting date trials may be needed to determine the optimal planting time for hemp in a particular region. Auto-flowering cultivars exist that will initiate flowering a certain number of days after seeding, but they require nuances in production and they can be prone to stresses early in growth. Regular testing for THC during flowering is also recommended so producers can be sure to harvest their crop if THC levels begin to approach the legal threshold during flower maturation. Working with local agencies is critical to ensure regulations are followed.
Stay tuned for the next article in the series coming soon: ““Integrated Pest Management and Implications for Wildlife,” by Dr. Susan Rupp.
About the author: Dr. Susan Rupp is V.P. of the Land & Natural Resource Section at Lee Enterprises Consulting, the world’s premier bioeconomy consulting group, with more than 150 consultants and experts worldwide. The opinions expressed herein are those of the author and do not necessarily express the views of LEC.
Kaiser, C., C. Cassady, and M. Ernst. 2015. Industrial hemp production. University of Kentucky Cooperative Extension Service, University of Kentucky College of Agriculture, Food, and Environment.
Mitchell, B. A., and M. E. Uchanski. 2020. Industrial hemp: reemergence of an alternative crop in the U.S. Fact Sheet 0.311. Colorado State University Extension. Fort Collins, Colorado.
Pal, L. and L. Lucia. 2019. Renaissance of industrial hemp: a miracle crop for a multitude of products. BioResources 14(2):2460-2464.
Salentijn, E.M.J., Q. Zhang, S. Amaducci, M. Yang, and L. M. Trindade. 2015. New developments in fiber hemp (Cannabis sativa L.) breeding. Ind. Crops Prod. 68:32-14.
Williams, D. W. and R. Mundell. 2018. An introduction to industrial hemp and hemp agronomy. University of Kentucky College of Agriculture, Food and Environment, Cooperative Extension Service.
Hemp Production for CBD – Revised
University of Nebraska-Lincoln Extension information typically is based on the interpretation of research information from Nebraska or elsewhere in the Midwest. However, such information is not available for hemp production due to previous restrictions on research in the U.S. This publication relies heavily on research findings from Europe and Canada and learning from growers’ experiences. See more stories in this series at https://cropwatch.unl.edu/tags/hemp.
Demand for CBD, a non-psychoactive compound derived from hemp, has soared for un-validated treatment of many conditions and illnesses. However, an approximate 75% plummet in prices for the CBD feedstock during 2019 indicates that the supply exceeded demand.
CBD-containing products marketed in the US range from cosmetics to chocolate bars to bottled water to pet treats, all with no regulation. The Food and Drug Administration warned marketers of CBD products against the use of non-validated health claims to sell their products. In June 2019 the FDA approved the first CBD-based drug, called Epidiolex, to treat seizures caused by extreme types of epilepsy. The efficacy of CBD for treatment of chronic pain, neuro-inflammation, anxiety, addiction, and anti-psychotic effects has not been well-validated by clinical research.
Hemp grown for CBD is a high-value crop grown more as a horticultural than as an agronomic crop. It has a high labor demand, putting US production at a disadvantage with production in China and other countries with relatively inexpensive labor.
Hemp CBD varieties have not been well-validated for Nebraska but possibilities may include ‘Abocus’, ‘Autopilot’, ‘Boax’, Cherry Wine, Cherry Blossom, Cobbler, and Sweetgrass for high pharmaceutical-grade CBD yield but having less than 0.3% THC.. High CBD varieties are generally grown only as female plants, as the combination of male and female plants leads to seed production and decreased CBD yield. Breeders continue to improve the processes for creating stable feminized seed. Farmers need to be wary of the source of their feminized seed stock and to check test results for validation of feminized seed.
Farmers need to know state regulations for testing hemp for CBD and THC. The Nebraska Department of Agriculture (NDA) regulations for industrial hemp production have been approved by USDA. Plant sampling by NDA staff to test for THC needs to be within 15 days before the date of harvest with the grower present during sampling. If the THC level is >0.3% by dry weight, the crop will not meet the legal definition of industrial hemp and need to be destroyed. Again, THC is expected to increase with stressful growing conditions.
CBD varieties have short plants with much branching, growing as squat bushes. The suggested spacing at this time is 2-4 feet x 6 feet. Planting practices may change for higher plant densities when seed supply is sufficient to greatly reduce the cost of seed. Given the high cost of seed, seedlings should be produced in a greenhouse for transplanting. If planting more than five acres, machine transplanting is recommended which may allow transplanting 2 acres per day. Plants can also be produced from cuttings with similar vigor and productivity compared to plants from seedlings. Propagation from cuttings may improve plant uniformity and is a means to all-female plants. The potting mix for greenhouse production of seedlings is important but needs to be well-drained with good available water holding capacity and nutrient supply. The mix probably should include sandy loam soil, perlite, and some organic material.
The CBD levels can be much reduced by cross-pollination with wild or non-CBD hemp. The CBD plants must be well-separated by distance or time of pollination from hemp weeds or another hemp crop. Also, a few rows of corn or forage sorghum can planted around the plots to reduce pollen flow.
The highest concentration of CBD is in the bracts of female flowers but CBD oil may be extracted from the whole plant. Harvest may be by topping plants for the harvest of mostly leaves and flowers, by picking the leaves and flowers from the plant, or by taking most of the plant cut at 8-12” above the ground. The whole plant harvest may be by shredding such as with a silage chopper or by keeping the plant intact.
Drying the plant material is a major operation as the water content is high when harvested. To reduce the quantity to be dried and handled for CBD production, the woody stems may be removed for land application, composting or dried separately for fiber production. Artificial drying at up to 100 o F should be continuous flow but the temperature of the plant material should not exceed 75 o F. Suspending plants or branches upside down by wires indoors out of the sun and with good air movement for air drying at up to 75 o F is a common practice if the harvest is not too large.
The ground-up plant material is soaked in grain alcohol or ethanol to extract the CBD oil. After soaking, the mix is pressed to extract the liquid. The alcohol is then evaporated off leaving the CBD oil.
Drying for smoke able buds is an option. Smoking of CBD is reported to be more effective than oral consumption. The buds are preferred but some upper leaves may be included. Well-dried material can be kept and sold in sealable plastic bags or glass jars.
Market information is too weak for prediction or advice but information is improving such as with a USDA ERS Feb 2020 report.
For information on budgeting for hemp grain, fiber and CBD production, see worksheets from Pennsylvania State University and from the University of Kentucky.