Does outdoor or indoor cannabis produce more terps and potent THC varieties?
A new study that compares outdoor and indoor cultivations expands on a fact familiar to experienced cannabis consumers. Plants grown outdoors express unique terpene profiles. And researchers found more rare THC varieties and terps in outdoor, sungrown cannabis compared to commercial, indoor production.
Scientists from two cannabis farms collaborated with researchers from the University of Columbia in New York. They grew two cultivars, Red Velvet (RV) and Cheetah Piss (CP), using three indoor and three outdoor clones. Quantification of each sample uncovered phenotypic diversity between the natural and commercial cannabis varieties.
They found rare intrinsic cannabinoids in outdoor grows. Plants cultivated inside instead expressed more oxidized metabolites, which are considered extrinsic to cannabis. (1)
Outdoor terpene profiles
Have you enjoyed sun-grown buds, wondering if their rich earthy tones come from the soil itself? The recent study published in Molecules concludes with a different question. It does, however, confirm that outdoor produces higher quantities of sesquiterpenes, including earthy and herbaceous isomers of caryophyllene. Indoor cultivars rather express more fragrant monoterpenes.
Raised beds supported the outdoor cannabis planted in a proprietary soil blend and fed compost. Both cultivars grown under the sun expressed more sesquiterpenes — including caryophyllene, α‐humulene, α‐bergamotene, α‐guaiene, and germacrene-beta. And Selina-diene and germacrene dominated outdoor samples of Red Velvet. Interestingly, indoor samples of both cultivars lacked the monoterpene beta-myrcene.
While a green light spectrum induces fewer changes in cannabis compared to sunlight or blue LED, (2) the researchers suggest this outcome did not encourage their results. Unlike monoterpenes, such as limonene or myrcene, different glands produce cannabinoids than sesquiterpenes. This writing author instead surmises that more acute sesquiterpene expression indicates that outdoor cannabis prefers Sessile Trichomes as environmental defense shields.
The paper, however, further implies that producers select indoor cultivars with narrow profiles. Their hypothesis suggests that market demand, combined with commercial production practices, slowly watered down the plant’s global terpene expression.
Indoor cannabinoids are oxidated
Plants grown inside under artificial light produce more extrinsic cannabinoids, which means the molecule has reacted with its environment. Activated D9-THC is extrinsic because cannabis plants naturally express acidic cannabinoids. This author suggests that oxidated cannabinoids in indoor cultivations grown in synthetic media are a result of depleted microbial content in the soil.
Cannabis’s natural microbiome uses oxygen compounds uptaken from the plant’s root system to synthesize nitrate compounds. Nitric oxide species, for example, can be metabolized by bacteria that dispose of their waste as nitrates. (3) A depleted microbiome content cannot properly use up reactive oxygen species that inevitably build up inside the plant, converting cannabinoids and terpenes. The process, however, remains a hypothesis.
The study concluded with a different hypothesis. Terpenes also control the oxidative environment within trichomes. The environmental change impacts terpene content, which ultimately affects the plant’s ability to maintain homeostasis. And so cannabinoid oxidation occurs in a less stressful environment due to the lower phenotypic need for terpenes.
Potent form of THC in outdoor cannabis
Clones from both cultivars produced differing levels of THCa and CBCa grown outdoors. CBGa prospers more abundantly in outdoor plants. Whereas THCa levels are greater inside and CBD varies between commercial and natural cultivation practices. Under sunlight, though, cannabis expresses greater quantities of the rare cannabinoid, CBC-C1.
Outdoor cultivation expresses rare and more potent forms of THC. Researchers identified higher expressions of butyl-THC (THCb) and hexyl-THC (THCh). These THC analogs are similar to D9, but they with a shorter and longer side-chain, respectively.
Hexyl-CBG should metabolize into THCh, but the mother of hexyl cannabinoids has yet to be found in cannabis. Tiny amounts of natural THCh remain difficult to quantify due to a similar compound known as O-methyl-Δ9-THC. (4) Minor cannabinoids avoid oxidation in sun-grown plants. But for now, we do not know why outdoor cannabis expresses more rare intrinsic cannabinoids than indoor plants.
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Morello V, Brousseau VD, Wu N, Wu BS, MacPherson S, Lefsrud M. Light Quality Impacts Vertical Growth Rate, Phytochemical Yield and Cannabinoid Production Efficiency in Cannabis sativa. Plants (Basel). 2022;11(21):2982. Published 2022 Nov 4. doi:10.3390/plants11212982
Micci A, Zhang Q, Chang X, et al. Histochemical Evidence for Nitrogen-Transfer Endosymbiosis in Non-Photosynthetic Cells of Leaves and Inflorescence Bracts of Angiosperms. Biology (Basel). 2022;11(6):876. Published 2022 Jun 7. doi:10.3390/biology11060876
Linciano P, Citti C, Russo F, et al. Identification of a new cannabidiol n-hexyl homolog in a medicinal cannabis variety with an antinociceptive activity in mice: cannabidihexol. Sci Rep. 2020;10(1):22019. Published 2020 Dec 16. doi:10.1038/s41598-020-79042-2