NOTE: We just heard about a professional, science-based company making root zone inoculants that appear to be far superior to all other root zone products. This company is Impello Biosciences–check them out. We’ve asked them for third-party verification that their products work well. If they do provide scientific proof that their root zone inoculants work, they’ll be the first company to do so. In our testing of other brands, we’ve seen no results that justify using their products. Hopefully, Impello Bioscience products will be properly-designed, wholly effective bioinoculant products growers seek! Growers we trust tell us they trust Impello.

The marijuana root zone is the physical foundation of cannabis plant health, metabolism, and productivity.

In natural outdoor growing, marijuana roots are part of a co-evolved ecosystem that protects them and enhances their function, fueled by plant growth-promoting microbes (PGPM) and plant growth-promoting rhizobacteria (PGPR). These living organisms can be used by marijuana growers as “bioinoculants.”

PGPM produce substances that promote plant growth by increasing availability and uptake of nutrients in soil via phosphate solubilization, siderophore and indole-3-acetic acid production, nitrogen fixation, and suppression of plant pathogens.

PGPR increase plant growth rate and nutrients absorption—especially when plants are under stress from drought, heat, overfeeding or underfeeding, and pathogenic attack. They bind with roots using arbuscular mycorrhizal fungi (AMF) to increase root surface area, leading to increased, more-rapid nutrient acquisition.

Specific types of bioinoculants are useful from germination to harvest, and especially for getting seedling, clones, and transplants off to a great start.

Unless you’re growing outdoors in native or living soil with a soil ecosystem that evolved to include specific PGPM and PGPR species beneficial to marijuana roots, you must add quality, science-based bioinoculants if you want the healthiest root zone.

Unfortunately, growers see a confusing array of different brands of root zone products, with each brand claiming to have PGPMs and/or PGPR that work for marijuana roots. But as with so many other product niches in the marijuana cultivation supplies industry, there are big problems with most of these brands and their products, including:

  • They’re not manufactured properly.
  • They don’t contain the right species or any species at all
  • They aren’t “live in the bottle.”
  • They’re very expensive, and don’t give you sufficient return on investment.
  • They can cause huge messy problems in pure hydroponics systems such as water culture and in hydroponic reservoirs.
  • Organisms have a hard time “colonizing” your cannabis roots when you’re using inert root zone media such as rockwool, and in water culture systems.
  • The product uses carrier materials such as clay or cane sugar, which are not good for roots or root zones.

A successful microbial inoculant has to colonize external and internal parts of root tissues to establish a symbiotic interaction with roots. It must also successfully, persistently compete against other microorganisms, especially root pathogens.

Moreover, even if bioinoculants plant initially colonize the cannabis root zone, their continued effectiveness and longevity aren’t always guaranteed. In many cases, bioinoculants when first applied are vigorous and effective, but soon die off due to environmental factors and/or pathogens.

What’s more, some beneficial microbes should only be used early in your plant’s life, while others are best used only during bloom phase, but most companies that sell these products don’t make those distinctions.

Scientific testing to measure cannabis root zone health and bioinoculant efficacy is an emerging research field, not yet as precise and reliable as it should be, but science does show specific breeds of Pseudomonas, Bacillus, Azospirillum brasilense, Gluconacetobacter diazotrophicus, Burkholderia ambifaria, and Herbaspirillum seropedicae species have root zone effectiveness leading to increased rooting, transplant success, growth rate, nutrients absorption, harvest weight, potency, and desirable cannabinoid profiles.

Bioinoculants can also be used as a cannabis foliar spray to attack Botrytis cinerea (gray mold/bud rot) and Trichothecium roseum pathogens commonly found on cannabis plants, especially outdoors. These pathogens damage leaves, flowers, stems and branches.

Indoor cannabis plants are also harmed by Golovinomyces, which causes powdery mildew (PM). PM is a severe fungal disease that ravages leaves and buds, and is often seen in indoor cannabis production.

Some marijuana growers use foliar fungicides, sulfur, bicarbonates, horticultural oils and other substances to fight powdery mildew and botrytis, but these sprays always cause at least minor harm to plants and are not safe (or pleasant to taste) on mature buds. Spraying anything on plants after buds are developed INCREASES the risk of bud rot.

Adding pure humic acid to root zone feeding with Bacillus subtilis and Pseudomonas aeruginosa has been shown to potentiate bioinoculant effects leading to increased nutrients absorption and production of beneficial root zone compounds.

Some growers believe adding molasses or other sugars to the root zone feeds bioinoculant organisms. This could be true, but also can quickly lead to a toxic root zone that provides ideal habitat for pathogenic microbes and/or pests.

We personally tested 17 different powdered or liquid bioinoculants brands marketed to cannabis growers, but never saw positive difference in root mass, root health, or plant health between plants without the bioinoculant versus those given bioinoculants.

When we ask manufacturers of those products for third-party scientific proof their products contain the right microbial species for cannabis, are bioactive on the shelf and after opening, and produce the claimed benefits, they refuse to provide any or sufficient information. And some were openly hostile to being asked to provide proof.

You may have heard that “compost tea” benefits your cannabis root zone due to bioinoculants on-board. We’ve tested several different starter kits and organic tea-making methods, but saw no benefits, and later found studies showing compost tea has no positive influence on cannabis root zone bacterial diversity, root health, or plant performance.

Be aware that some bioinoculant products create harmful blooms in hydroponic reservoirs and systems, and water containing chloramine and/or chlorine (found in almost all municipal tap water) kills beneficial root zone microbes.

Further, in most pure hydroponics systems and sterile root media such as rockwool, beneficial microbes aren’t able to anchor properly.

Using living soil and homemade compost full of beneficial microbes is very smart; growers using those popular hype-marketed root inoculant brands are wasting their money.

We’ve done many side by side tests comparing root development of plants treated with root zone inoculants versus those that were not. There was no evidence those products helped at all. Worse yet, some damaged the root zone and roots because of inferior carrier materials such as clay or sugar, and other product flaws.

But as noted above, we might have discovered the one legit company making root zone bioinoculants that boost your plants’ health, growth rate, and harvest rewards. Keep checking our magazine to see an update on that.