First and foremost, the failure of high CBD hemp in Arizona, USA, is a market consequence. Because of the low prices for CBD (Jibilian 2019) and limited infrastructure in Arizona, hemp does not appear to be a viable crop currently for Yuma County. The other reasons behind the failure of high CBD hemp as a crop in Arizona can be attributed to the plant’s own life history and a lack of familiarity with it on the part of the farmers. The first likely problem was that the seed farmers obtained were not bred for seed-based agricultural applications. Cannabis strains that produce high yields of CBD were first bred from high THC strains used in the indoor medical/recreational cannabis industry (Grassa et al. 2021). Small-scale greenhouse or indoor growing of THC strains primarily utilize clonal propagation or purchase of seed from established sources utilizing stable varieties. The newness of hemp and high demand for seed rushed the seed production process that could have resulted in seeds of varying quality. Previous research into the genomics of CBD producing hemp strains demonstrates that the high CBD-producing varieties are a paraphyletic group, with fiber and grain producing strains nested within the CBD clusters (Johnson and Wallace 2021). The most reasonable explanation for this is that high CBD strains have been bred repeatedly from other hemp strains and are not a group defined by a single high CBD-producing ancestral strain. This research also demonstrated that even within a single variety of CBD-producing hemp, there was large amounts of variation, with some strains having variation that scattered across the entire 173 plant phylogenetic tree (Masson 2020a).

Some of the problems that this variation can present to outdoor farming operations often involve the photoperiod of the cannabis plant. Cannabis is a short-day plant, meaning it will start to flower when the length of daylight falls below a certain amount (Hall et al. 2012). Cannabis varieties in the past had been bred to flower at various day lengths, to adapt the plant to different latitudes where growing takes place (Small 2017). Since CBD is produced in trichomes around the female flower, getting the plant to produce flowers is essential to commercial success. Having plants that flower too late or too early can greatly reduce the amount of usable inflorescence biomass for CBD extraction that the farmer is able to harvest. In Yuma County, this often meant that hemp plants would flower too early, resulting in a much smaller plant at maturity and a significant loss of inflorescence biomass available for harvest and extraction (Masson 2021).

Other problems with the plants involved the production of THC and terpenes. Plants that produce more than 0.3% Δ⁹-THC by dry weight are no longer considered hemp (first proposed by (Small and Cronquist 1976)) and must be remediated by mixing biomass with flowers and retested (Masson 2021). Informal estimates from communications with the farming community as well as data reported in this study revealed that about one-third of Arizona, USA’s CBD crop was destroyed each year because of THC overage. Since both CBD and THC are produced from the same precursor, olivetolic acid (Flores-Sanchez and Verpoorte 2008), their presence in hemp plants is strongly related to each other. Thus, a relaxation of the allowable THC content below 0.3%, the current legal limit, would be beneficial to the industry. Given that a 1% Δ⁹-THC content is widely recognized as the minimum amount to induce a noticeable intoxicating effect (Small 2018), there appears to be room to raise this limit. The original 0.3% limit proposed by Small and Cronquist (1976) was described by the authors as arbitrary and certainly has little direct support from physiological research. Also, the high CBD hemp had a strongly unpleasant odor, almost certainly from the terpenes that the plant synthesizes along with cannabinoids. These terpenes are highly valued in the medicinal/recreational cannabis industry, giving the inflorescences used for medical and recreational consumption their unique smells and flavors (Booth and Bohlmann 2019). The terpenes are usually removed in the process of extracting and purifying CBD, but their presence in the crop was a real deterrent for the farmers and their neighbors.

While there were many failures during the boom and bust of hemp in Arizona, USA, there are some glimmers of hope. The U of A outreach program was able to identify three successful growers in Yuma. One was a small-scale grower. A second farmer mostly profited on agro-tourism, hosting parties, and providing a novel “pick-your-own hemp” roadside stop. A third farm was managed intensively to harvest before the crop exceeded the legal THC limit. These cases demonstrate that there can be success growing hemp for CBD in Arizona, USA. However, the bust has already driven many potential farmers away from hemp as a crop. While growing for CBD may be an unrevivable industry, there is still room for lower CBD hemp to be successful when grown for fiber or other uses. Additionally, hemp may provide a value-added option to remove environmental contaminants as a new phytoremediation crop in Arizona, USA (Wu et al. 2021). Phytoremediation is the use of plants to clean up soil or water from toxic contaminants such as heavy metals or organic pollutants. The Arizona Department of Agriculture has recently taken several steps to support hemp agriculture, such as allowing farmers to be eligible for federal programs including the Noninsured Crop Disaster Assistance Program and Easement Program Farm loans, as well as allowing the export to other states of hemp nursery products including seedlings and rooted cuttings ( Arizona Department of Agriculture (AZDA) 2022).

At the time of writing, only ca. 60 acres of hemp grow exists in Arizona, USA. Most of the hemp products being sold in Arizona, USA’s market are not from hemp grown in the state. Future production in hemp can utilize varieties that have been selected for different parts of the plant that have commercial value, such as high-fiber or seed production. Currently, varieties are well established that can be grown for fiber or seed (used for seed oil or as a food or feed crop). Selecting strains that would be successful in the climate of Yuma County should start with varieties bred for similar climates in other regions of the world. Leafy greens, or microgreens, are leaves harvested from young plants and are currently prized by consumers for their nutritional qualities and flavor (Martínez-Sánchez et al. 2012). Recently, the use of hemp to grow microgreens has also been developed (Mi et al. 2020) and represents a large and untapped potential for hemp agriculture. Nontraditional products can also be made with hemp, such as hempcrete. Hempcrete is a form of concrete that is made with hemp shives, the part of the stem not used for fiber production. Hempcrete has been found to have better sound insulation properties and an ability to regulate relative humidity inside of buildings (Lupu et al. 2022), as well as being a potential carbon sink to help reduce the causes of climate change (Kumar et al. 2021).

Any discussion of sustainable agriculture in Arizona, USA, must also consider the current state of water resources. Arizona is an arid state, and water for agriculture is provided from surface waters such as the Colorado River in the case of Yuma County. Colorado River water is a disappearing resource, and recently, the federal government has asked the states of the Colorado basin to revise their allotted amounts of river water based on the decline of reservoirs in the system due to climate change (Vasilogambros 2022). Hemp for fiber has been suggested as an alternative to water intensive crops such as cotton, and some research claims that it uses half as much water as the latter (Rosa and Grammatikos 2019), though this was not the objective of the cited study. Research into water usage in hemp grown in southern Italy demonstrated that bisexual varieties cultivated for fiber used 250-mm (almost 10 inch) water, and dioecious varieties also bred for fiber used 450 mm (almost 18 inch) (Cosentino et al. 2013). Research on water use in hemp crops grown in Tasmania found it possible to grow the crop with between 359 mm (14 inch) and 535 mm (21 inch) of water, although significant yield differences were found between different water levels (Lisson and Mendham 1998). Other research conducted in Spain demonstrated the ability to grow hemp as a fiber crop with 960 mm (38 inch) up to 1200 mm (47 inch) of water, again showing significant differences in the yields for different irrigation levels (García-Tejero et al. 2014). Research in Arizona has noted that cotton crops grown in Maricopa County consume 1050 mm (41.2 inch) of water for a growing season (Erie et al. 1965). While this number is higher than most of the amounts used by hemp cited, it is not greater than all of them, suggesting that hemp may not be the water-saving crop some have claimed. Furthermore, none of the hemp studies cited above was conducted in desert environments similar to Arizona or with hemp varieties that are grown for high CBD production. Given the lack of suitable comparisons, any claims of water conservation from replacing cotton (or any other crop) with hemp are speculative at best until supported with research from arid environment agricultural systems.