Last updated on September 18, 2026 · Originally published May 12, 2022
Cannabinoid content in plants can vary greatly depending on abiotic factors such as light, temperature, humidity, water availability, and nutrients. [1] Nevertheless, it’s not only climatic conditions that influence cannabinoid biosynthesis but also cultivation practices – from soil building techniques to mineral amendments like zeolites – plant genotypes, and the plethora of microorganisms present in the soil.
Biostimulant substances, plant growth-promoting rhizobacteria (PGPR), and mycorrhizal fungi have been employed by growers in the attempt to maximize the yield of cannabis plants and stabilize their chemical composition – the working premise behind living soil cultivation. However, scientific research on the manipulation of soil microorganisms’ taxonomic composition and cannabis plant–microbiota interactions has focused mainly on well-known PGPR genera such as Pseudomonas and Bacillus, investigating their beneficial functions, pathogen tolerance, secondary metabolite biosynthesis, and stress response.
How Do Cultivar and Environment Shape the Microbiota?
The cannabis soil microbiota is shaped by the cultivar – but not by the cultivar alone. Different cannabis varieties host measurably different microbial communities, with the strongest cultivar signal found belowground, [2] and soil characteristics and cultivar together shape the cannabis microbiome. Yet the same study found that growth stage and plant compartment drove even clearer community shifts, and its authors note that across plant–microbiome research more broadly, the growing substrate is generally the primary factor dictating community composition. [2] High-throughput sequencing can identify microbial taxa associated with cannabis roots and show how those communities vary by cultivar, plant compartment, and growth stage. It cannot, by itself, establish that the plant deliberately recruited a microorganism or that the association benefits either partner. The importance of studying the natural microbial composition of microbe-rich organic soil is linked to the possibility of a neutral or even antagonistic effect if an unspecified microbiota is introduced into the native soil community.
From Core Microbiota to Bioinoculants
Identifying the core bacterial and fungal communities associated with particular cultivars could eventually help researchers design inoculants that improve plant health, below-ground nutrient cycling, or chemical consistency. Metagenomics can help identify microbial communities, while metabolomics can reveal associations between those communities and plant chemistry – but neither establishes causation by itself. Controlled inoculation experiments are needed for that, which is why the studies below matter.
When this article was first published in 2022, that closing thought was a proposal – the central idea of a 2021 review by Bulbul Ahmed and Mohamed Hijri. [1] An early PGPR study had already pointed the same way: inoculating hemp with a four-species rhizobacteria consortium improved growth and the accumulation of secondary metabolites in the ‘Finola’ cultivar. [3] But whether deliberately steering the soil microbiota could change cannabinoid output in medical cannabis remained an open question.
Did Manipulating the Microbiota Actually Work? The 2023 Follow-Up
The same research group went on to test the idea. In a greenhouse trial published in 2023, five medical cannabis cultivars were grown either uninoculated or under one of three inoculant treatments: a commercial consortium containing the mycorrhizal fungus Rhizophagus irregularis, Trichoderma harzianum, Bacillus subtilis, and a microalga; a microbial suspension obtained from forest soil; or the forest suspension supplemented with R. irregularis. [4]
The inoculants altered cannabinoid concentrations – but not uniformly. Significant differences in cannabidivarinic acid (CBDVA), cannabidivarin (CBDV), cannabigerol (CBG), CBD, and cannabigerolic acid (CBGA) were observed across cultivars under inoculation. Biomass was measured separately: three of the five cultivars produced more plant biomass under the treatment combining the forest microbial suspension with R. irregularis. [4] The effects, however, were strongly cultivar-specific: which cannabinoids shifted, and under which treatment, changed from variety to variety, and some compounds showed no treatment effect at all in some cultivars.
Three caveats keep this from being a grower-ready recipe. The trial ran in a coconut coir–perlite substrate in a controlled greenhouse, not in field soil, so it demonstrates the principle rather than a living-soil practice. The inoculants were applied once, at establishment. And the persistence question stayed open in an instructive way: none of the deliberately added organisms appeared in the sequencing dataset at harvest – but the sequencing method was not well suited to tracing R. irregularis, and microscopy did confirm mycorrhizal colonization in some treated roots. The experiment therefore leaves inoculant persistence unresolved rather than showing that the added microbes disappeared [4] – a close cousin of the concern the original review raised about introducing an unspecified microbiota into an established community. Terpenes, notably, were not measured at all: for the flavor and aroma side of the equation, the evidence base is thinner still. For the wider inoculant landscape, including the products and mycorrhizal findings growers ask about most, see our companion piece on beneficial microbes for cannabis cultivation.
A second 2023 experiment showed how strongly the outcome can depend on nutrition. In the cultivar CBD Kush, bacterial inoculation produced no significant cannabinoid changes under the recommended nutrient regime, and trichome densities generally trended downward with inoculation. Under reduced nutrition the picture flipped: inoculated plants tended to carry more trichomes, though only the increase on calyces under the Bacillus–Pseudomonas consortium was significant against the uninoculated low-nutrient control. Low nutrition by itself pushed THCA and CBDA upward relative to recommended feeding even without an inoculant – significantly so for THCA. The microbial effects layered on top were mixed: among Bacillus-treated plants, delta-9-THC was 51% higher under reduced nutrition than under recommended nutrition, while the consortium treatment was associated with lower concentrations of several cannabinoids. [5] The lesson is not that one bacterium reliably raises potency, but that microbial effects depend on the surrounding cultivation conditions.
Where Does the Science Stand Now?
A 2026 review of the cannabis microbiome literature reaches a conclusion very close to where this article started: microorganisms can modulate cannabinoid and terpene profiles, but the responses are cultivar-specific, many proposed mechanisms remain hypothetical at the molecular level, and long-term field-scale trials are still largely missing. [6] Genotype-tailored microbial formulations – matching the inoculant to the microbial community associated with that cultivar – are the direction the field is now pointing. [2,6] The evidence now shows that microbial treatments can alter cannabis growth and chemistry under controlled conditions. What remains unknown is whether those effects are reliable across facilities, soils, and repeated crop cycles – and which organism, cultivar, and nutrient regime must be matched to reproduce them.
Scientifically reviewed by Chana Frenkel, Ph.D.
References:
[1] Ahmed B, Hijri M. Potential impacts of soil microbiota manipulation on secondary metabolites production in cannabis. J Cannabis Res. 2021;3(1):25. doi:10.1186/s42238-021-00082-0
[2] Comeau D, Novinscak A, Joly DL, Filion M. Spatio-temporal and cultivar-dependent variations in the cannabis microbiome. Front Microbiol. 2020;11:491. doi:10.3389/fmicb.2020.00491
[3] Pagnani G, Pellegrini M, Galieni A, D’Egidio S, Matteucci F, Ricci A, et al. Plant growth-promoting rhizobacteria (PGPR) in Cannabis sativa ‘Finola’ cultivation: An alternative fertilization strategy to improve plant growth and quality characteristics. Ind Crops Prod. 2018;123:75–83. doi:10.1016/j.indcrop.2018.06.033
[4] Ahmed B, Beneš F, Hajšlová J, Fišarová L, Vosátka M, Hijri M. Enhanced production of select phytocannabinoids in medical Cannabis cultivars using microbial consortia. Front Plant Sci. 2023;14:1219836. doi:10.3389/fpls.2023.1219836
[5] Tanney CAS, Lyu D, Schwinghamer T, Geitmann A, Ruan ED, Smith DL. Sub-optimal nutrient regime coupled with Bacillus and Pseudomonas sp. inoculation influences trichome density and cannabinoid profiles in drug-type Cannabis sativa. Front Plant Sci. 2023;14:1131346. doi:10.3389/fpls.2023.1131346
[6] Wiszpolski PS, Stolarski MJ. The role of the rhizosphere, endophytes, and the influence of plant-growth-promoting bacteria: Take the cannabis microbiome as an example. Int J Mol Sci. 2026;27(11):4802. doi:10.3390/ijms27114802
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