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Optimising plant yield with beneficial microbes

Okay, class, hands up; who wants to optimise their yield? Everyone? Well, that was easy. The good news is that this can be done safely, naturally, and fairly easily via the introduction of beneficial microbes.

What are beneficial microbes?

Put simply, microbes are tiny life forms, so small that they can only be viewed under a microscope. In this article, we’re interested specifically in soil-dwelling microbes. The relationship between microbes and plants is ancient and complex. The two have evolved over millennia (really!) to become almost entirely dependent upon each other.

Some microbes are good, and some microbes are bad. You can stack the odds in your favour by adding more of the good ones to play a solid defensive game. When added to the soil, these organisms can attack and fend off harmful microbes and pathogens, which could potentially spell disaster for your beautiful crops. So, it makes sense to add them to your arsenal whether you grow indoor or outdoor.

How do these microbes help to increase yield?

Microbes basically boost growth by flooding extra nutrients to the plant. These heroic organisms allow the plant greater access to vital nutrients within the soil, such as nitrogen, phosphorous and potassium. As a thank-you, the plant’s roots release substances called exudates – for example, amino acids and photosynthesis-derived sugars – back into the soil, offering additional welcome nutrition to the microbes. There are two main essential types of beneficial microbes growers can use for yield optimisation, these are:

Mycorrhizae – these are fungus in the rhizosphere (the area of soil around the plant roots where chemistry and microbiology are influenced by the growth and nutrient exchange of the roots). These can be intracellular or extracellular[i] and form relationships with the plant, resulting in balanced nutrient sequestration in saline environments, positively affecting the sodium to potassium ratio within the root tissue and increasing the root surface area [ii].

Rhizobacteria – are bacteria-plant associations, often referred to as PGPR – Plant Growth Promoting Rhizobacteria, and these can stimulate crop growth and increase overall vigour by improving stress tolerance[iii]. This is typically achieved by any one of the following means:

  • Production of phytohormones for growth signalling, or priming against pathogenic attack
  • Increasing nitrogen fixation and phosphate solubility, along with chelation of heavy metals
  • Increased competition for pathogenic microbes, thus decreasing the chances of a negative infection[iv]

While much research has been carried out to test the ability of PGPR to increase yields in crop plants such as rice, wheat, sugarcane, and soybean, the efficacy of PGPR on cannabis plants has only been published as recently as 2018. The study showed a combination inoculum of Azospirillum brasilense, Gluconacetobacter diazotrophicus, Burkholderia ambifaria, and Herbaspirillum seropedicae increased the growth, yield and vigour of Cannabis species (v). In addition, the study showed an effect on the plant’s secondary metabolites, equating to an increase in cannabinoids, an increase in root mass and root hair production leading to an overall improvement in the plant’s ability to grow.

How to add beneficial bacteria

The easiest way to add beneficial bacteria to your environment is by using commercially available biostimulants, which can take several different forms and contain different strains of PGPR. Among the options available are:

  • Seed Treatments, which are to be applied prior to planting
  • Soil Drenching, where the product is typically diluted before being added to the soil around the root area
  • Foliar Sprays, which protect against outer-showing pathogens such as grey mould
  • Feeds, which can be added to your nutrient tank (but with certain notable caveats, for example, in hydroponics, do not add at the same time as disinfectants such as hydrogen peroxide or chlorine – wait 12-24 hours)[vi]

While mycorrhizae are especially useful in enhancing plant growth in soil, hydroponic systems are more favourable to bacteria due to the high nutrient concentrations and increased watering rate [vii]. With beneficial bacteria being available in various forms, at varying quantities and most certainly affordable, if you haven’t already incorporated these advantageous associates into your regimen, it’s certainly worth a try.

As with any new introduction to your growing regimen, do your homework, and take special care to make sure dilution instructions are followed correctly where applicable to ensure  A+ grades.


[i]Johnstone et al, 1997



[iv]Lyu et al, 2019




Cultivation information, and media is given for those of our clients who live in countries where cannabis cultivation is decriminalised or legal, or to those that operate within a licensed model. We encourage all readers to be aware of their local laws and to ensure they do not break them.

This post is also available in: French

Duncan Mathers