Industrial Hemp Production, Cultivation, and Management,
by: Susan P. Rupp, PhD (Lee Enterprises Consulting)
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 tetrahydrocannbinol (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 chemical that gives marijuana users their “high.” While marijuana cultivars typically contain more than 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 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 that have the characteristics most desirable for that market, and understand production challenges and environmental constraints for their specific region.
The purpose of this article is to give a basic overview of the different types of industrial hemp crops as well as agronomic considerations when growing those crops. Readers are encouraged to research regulations for industrial hemp production within their respective states as well as contact local 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 cannabidiols and is currently gaining attention for possible use in pharmaceutical markets. Some health conditions CBG is being researched for 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, distinctive from those 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, Cassady, and Ernst 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 an a more expensive, but reliable alternative in which stems are submerged for several days (Kaiser, Cassady, and Ernst 2015).
Hemp seeds are used in human food products, health supplements, personal hygiene products, lubricants, paints, solvents, hempseed oil (different from CBD oil), and other products. As a dietary supplement for humans, it contains a very 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, Cassady, and Ernst 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 at 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 will 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, Cassady, and Ernst 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, Cassady, and Ernst 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.
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 regardless of the day length. 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, Cassidy, and Ernst 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.
Hemp and Wildlife
The potential exists for industrial hemp production to have ecological benefits. Some hemp grown for seed, fiber, or dual-purpose (seed and fiber) are heavy pollen producers in the summer and serve as an off-season food source (no nectar is produced) for bees and other pollinators (Mitchell and Uchanski 2020). O’Brien and Arathi (2019) reported 20 different genera of bees on flowering hemp demonstrating that hemp in the agroecosystem supports pollinators. Pollinators contribute >$24 billion/yr to the U.S. economy, honey bees contribute ~$15 billion/yr, and native pollinators ~$9 billion/yr. Given pollination is required for >75% of food crops worldwide, hemp as a supplemental crop for pollinators could have economic benefits.
Despite the potential benefits to some pollinator species, hemp crops can be prone to a variety of insect pests that vary depending on where they are located within the U.S. In addition, regulatory barriers prevent the use of several insecticides and policies currently vary by state. Because pollinators are currently suffering major declines due to increased use of pesticides (which cause direct mortality to insects) and herbicides (which reduce available habitat), an integrated pest management (IPM) approach is ideal. Therefore, it is good practice for producers to contact their local Extension offices to seek information specific to their locales and to develop an IPM system to improve yields while reducing risks to beneficial ecosystem services. Additional production information and technical assistance can also be acquired through natural resource agencies such as the Natural Resources Conservation Service (NRCS), who administer Farm Bill programs.
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.
O’Brien, C. and H. S. Arathi. 2019. Bee diversity and abundance on flowers of industrial hemp (Cannabis sativa L.). Biomass and Bioenergy 122:331-335.
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.