Bacteria are ubiquitous. These single-celled organisms are found everywhere, from our digestive tracts to the soils that sustain us, and they stitch together the biological fabric of all complex life on Earth. A single teaspoon of soil can hold up to one billion bacteria. This incredible density of microbial life is critical to nutrient cycles, plant decomposition, and the health of entire ecological systems.
Certain species of bacteria can even dramatically improve the health and performance of cultivated plants. Called plant growth-promoting rhizobacteria (PGPR for short), these beneficial soil microbes have been used for decades to boost yields and the overall quality of key crops like soybean, corn, wheat, and rice.
Microbial inoculants containing PGPR have been proven to improve plant nutrient uptake, root development, and stress tolerance across dozens of plant species. New studies suggest that PGPR can confer these benefits to cannabis plants as well.
Cannabis growers are increasingly utilizing PGPR as a plant biostimulant to improve crop yields, reduce their use of conventional fertilizer, and sustainably produce high-quality cannabis. To understand the benefits, let’s take a look at why rhizobacteria are important, and what the science says about the potential benefits of PGPR in cannabis production.
What are Rhizobacteria?
Before getting into how plant growth-promoting rhizobacteria benefit cannabis plants, it is important to know what exactly rhizobacteria are, and what makes these microscopic wonders have such an outsized impact on plant growth.
Despite appearances, plants are not individuals. They are entwined in deep, complex relationships with the soil or substrate in which they grow. Plants and soil microbes interface through the rhizosphere, the thin layer of soil that surrounds plant roots. The complexity of connection and activity in the rhizosphere blurs the boundaries between plant and non-plant. The rhizosphere has even been called an “information super highway”, given the incredible density of interactions and chemical signals exchanges between plant roots and soil microbes.
Bacteria that inhabit this world connecting worlds are classified as rhizobacteria. Most are useful, some can be parasitic, and about 2-5% are beneficial to plant growth—the so-called plant growth-promoting rhizobacteria.
These PGPR enhance plant access to nutrients, produce growth-stimulating hormones, and enforce symbiotic relationships that protect plants from parasitic microbes, pests, and abiotic stresses like drought, salinity, and extreme heat.
Plant Growth-Promoting Rhizobacteria in Agriculture
PGPR have been used as plant biostimulants for over a century, beginning with rhizobacterial inoculations of legume crops. There is now extensive research documenting yield increases associated with certain rhizobacterial strains, particularly the Bacillus, Mucilaginibacter, and Pseudomonas genera of bacteria.
Microbial inoculants with one or multiple PGPR improve yields by encouraging plant growth through various mechanisms, including:
- Facilitating biological nitrogen fixation
- Increasing the bioavailability of key nutrients, like phosphorus and potassium
- Producing growth stimulating plant hormones
PGPR microbial inoculants can also boost yields by improving disease control and plant stress tolerance. Many species, including the genera Bacillus, Paenibacillus, and Pseudomonas are effective biocontrol agents. They produce antibiotics, along with pathogen-killing metabolites, and encourage plants to do the same. Some rhizobacteria species successfully control powdery mildew in strawberry, pea, and cucumber crops, and may protect cannabis similarly.
Plant Growth-Promoting Rhizobacteria for Cannabis Production
Although the yield-boosting benefits of PGPR are well documented in many crops, prohibition limited research into their effect on cannabis, but that is now changing. Several recent studies observed that inoculating cannabis plants with PGPR can enhance plant growth, and may even influence cannabinoid production.
Some demonstrated benefits of inoculating cannabis crops with PGPR include:
Improving Cannabis Root Development: In a 2022 study, Cannabis sativa cuttings inoculated with Bacillus species produced a 13% increase in root length. Stronger root development enhances plant growth and stress resilience.
Increasing Flower Weight and Number: In the same study, a Bacillus species inoculation increased flower number, axillary bud outgrowth rate, and total flower weight by 5.13%. Another study of Cannabis sativa observed a 16% boost in yields when applying a microbial inoculant to plants in hydroponic and soil-less growing systems.
Improving Secondary Metabolite Accumulation: PGPR inoculation may have a positive effect on THC and CBD concentrations. THC, CBD, and other cannabinoids are secondary metabolites: compounds not essential for plant growth or reproduction, but may provide other benefits. PGPR alters secondary metabolite accumulation in many plants, and early evidence suggests they could positively affect cannabinoid production too.
PGPR and Sustainable Cannabis Production
Synthetic fertilizers are a major source of emissions and freshwater pollution and are routinely over-applied on most crops, including cannabis. Likewise, the overuse of chemical pesticides often decimates the very soil microbes that contribute to plant health and disease resistance, resulting in a vicious cycle that requires ever more pesticide use.
Demand for cannabis and hemp is expanding rapidly, and how it is grown will have profound implications for our planet. Replacing some synthetic inputs with microbial inoculants is one way to work with nature to support plant growth, crop quality, and disease resistance, all while reducing emissions and building healthy soils and rhizospheres.
And as abiotic stresses like drought and extreme heat become more common with every passing year, prioritizing the health of the rhizosphere will become even more critical. PGPR can help plants weather uncertain and demanding conditions—building some much-needed resilience into both individual crops and our larger agricultural systems.
Applying PGPR for Outdoor and Indoor Cannabis Cultivation
Incorporating plant biostimulants like PGPR reduces reliance on synthetic inputs for outdoor and indoor cannabis cultivation, offering one potential solution for cannabis growers looking to prioritize both sustainability and exceptional quality.
Microbial inoculants like Impello’s Continuµm™ can work in any environment, any growing medium, and any irrigation system. With an inoculating blend of naturally occurring Bacillus & Paenibacillus species, Continuµm™ is a finely tuned blend employing advanced fermentation techniques to ensure the rhizobacteria continue to thrive after application.
Continuµm™ can be applied at all stages of plant growth, as a root drench or foliar spray for cannabis plants in hydroponic, soilless, soil-based, and field cultivation systems. Regular applications of PGPR—as often as every watering—encourage rapid plant growth, root development, and stress resilience. Nutrient availability and water retention will improve, helping optimize yields and quality. It is OMRI certified for organic use and compatible with any fertilizer program.
Learn more about PGPR dosing, application guidelines, and the power of Continuµm™ here, and drop us a line at email@example.com if you have more questions about how PGPR can benefit your cannabis production!
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