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Authors: Dongmei Lyu a,* , Eric D. Ruan b, Rachel Backer a, François Gagn ́e-Bourque c,Donald L. Smith a,* a Department of Plant Science, McGill University, Sainte-Anne-de-Bellevue
Today, we’re diving into an exciting study that explores how microbial biostimulants and growing substrates can reshape cannabis growth and chemistry. Published in Industrial Crops & Products (2025), this research investigates how Beneficial Bacillus bacteria interact with two substrates—coco fibre and potting soil (Promix)—to boost cannabis performance.
Study Setup
The team grew Cannabis sativa in a controlled indoor environment, comparing two substrates: pure coco fibre and a potting soil mix (sphagnum peat moss and perlite). They introduced a microbial biostimulant—Microbial Mass, a consortium of five Bacillus strains, applied at specific intervals during the vegetative and flowering stages. The goal? To measure impacts on plant growth, biomass, and phytochemicals like cannabinoids and terpenes across the plant’s life cycle.
Key Findings
Here’s what they uncovered:
Growth and Biomass:
Coco fibre shone early, delivering significantly higher root production at the vegetative stage—think robust root systems setting the stage for growth. With Microbial Mass, roots got an extra boost.
Potting soil (Promix) took the lead later, driving greater overall biomass—leaves, stems, and flowers—at flowering and maturity. Plants here grew taller and produced 1.7 times more flower dry weight than in coco fibre. With biostimulant inoculation, leaf biomass in Promix jumped by 45% compared to coco fibre controls.
Plant Health (SPAD Values):
Promix plants boasted higher chlorophyll levels (measured as SPAD values) across all stages, signaling healthier, greener leaves. At mid-flowering, Microbial Mass gave Promix plants an extra chlorophyll kick—vital for photosynthesis and vigor. Coco fibre lagged, hinting at nutrient retention challenges.
Cannabinoids:
Biostimulant inoculation supercharged key cannabinoids—CBDA, THCA, and CBD showed significant boosts (p ≤ 0.05). Promix amplified CBD, Δ⁹-THC, and CBC even further, while maintaining a steady CBDA:THCA ratio (1.49:1) across treatments. Coco fibre, despite lower yields, nudged up cannabinoid concentrations—possibly a stress response to limited nutrients.
Terpenes:
Total terpene levels spiked by 5% in coco fibre with Microbial Mass—aromas and flavors got a lift! Promix didn’t see this boost, suggesting substrate properties steer terpene synthesis.
Substrate and Microbial Dynamics
Why the differences? Coco fibre’s aeration fuels early root growth but struggles to hold nutrients long-term, while Promix’s richer mix sustains plants through flowering. The Bacillus consortium in Microbial Mass enhances nutrient uptake and plant health—think of it as a microbial teammate unlocking phosphorus, potassium, and more. These effects vary by substrate, highlighting a tag-team effort between soil type and microbes.
Practical Implications
Want max yield and healthy plants? Potting soil with Microbial Mass could be your go-to, delivering bigger harvests and robust growth.
Chasing potent cannabinoids or terpenes? Coco fibre with biostimulants might edge out higher concentrations, though you’ll need extra fertigation to keep plants thriving. This study underscores a sustainable edge—microbes could cut reliance on chemical fertilizers, boosting both profitability and eco-friendliness.
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