# Bottled microbes and additives: a fair tier list for cannabis growers

> Some bottled microbes really do help keep root rot away, but by protecting roots, not by feeding the plant. Trichoderma, Gliocladium (Clonostachys), Bacillus and Streptomyces products have research behind them against Pythium and Fusarium root rots, and some are registered for use on cannabis. Mycorrhizae help mostly in low-phosphorus soil and many commercial products fail to colonise roots. 'Nutrient-boosting' microbe blends and compost teas have the weakest evidence in a fully fed room.

- Canonical: https://genetixbay.com/knowledge/diseases/bottled-microbes-tier-list.html
- Category: Diseases · Level: Intermediate
- Evidence: Supported · Status: Draft: awaiting expert review (some figures are being checked)
- Stage: Any stage · Systems: Any system
- Updated: 2026-11-02 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)"

## Questions and answers

**Do beneficial microbes work for cannabis?** Some do, within reason. Trichoderma, Gliocladium (Clonostachys), Bacillus and Streptomyces products have research showing they reduce [Pythium](https://genetixbay.com/knowledge/glossary/pythium.md) and [Fusarium root rots](https://genetixbay.com/knowledge/glossary/fusarium-wilt.md) in greenhouse crops, and some are registered for use on cannabis in Canada. They work by protecting roots, not by feeding the plant. [Mycorrhizae](https://genetixbay.com/knowledge/glossary/mycorrhizae.md) and 'nutrient-boosting' blends have weaker evidence in fully fed rooms.

**Which beneficial microbe is best for [root rot](https://genetixbay.com/knowledge/glossary/root-rot.md)?** The best-supported root-rot protectants are Trichoderma harzianum, Gliocladium (Clonostachys) catenulatum, Bacillus subtilis or amyloliquefaciens, and Streptomyces griseoviridis. In greenhouse [rockwool](https://genetixbay.com/knowledge/glossary/rockwool.md) trials, products based on these reduced Pythium and Fusarium root rot severity. Apply them preventively, at planting or from the start, and follow the label and local rules for cannabis.

**How do beneficial microbes protect roots?** [Biocontrol](https://genetixbay.com/knowledge/glossary/biological-control.md) microbes protect roots in four main ways: they crowd pathogens out of the root surface (competitive exclusion), make antibiotic compounds (Bacillus lipopeptides, for example), attack the pathogen directly (Trichoderma coils around and digests other fungi), and prime the plant's own defences (induced systemic resistance). None of that is feeding the plant.

**Do mycorrhizae help in [coco](https://genetixbay.com/knowledge/glossary/coco-coir.md) or hydro?** Usually not much. Mycorrhizal fungi mainly help plants get phosphorus where it's scarce, so in a fully fed coco or hydro system there's little for them to add. In a cannabis seedling trial the highest dose raised root length 34% and phosphorus content 24%, but a global evaluation found most commercial inoculants failed to colonise roots at all.

**Can I use microbes and [hydrogen peroxide](https://genetixbay.com/knowledge/glossary/hydrogen-peroxide.md) together?** Not at the same time. Hydrogen peroxide and chlorine kill beneficial microbes as well as pathogens. GenetixBay's position is that a [beneficial-microbe reservoir](https://genetixbay.com/knowledge/glossary/beneficial-microbe-reservoir.md) is preferred, since bacteria arrive anyway, but a [sterile reservoir](https://genetixbay.com/knowledge/glossary/sterile-reservoir.md) is valid if you commit to it fully. Pick one approach and stick to it.

**Short answer, in plain words.** Some bottled microbes really do help, mostly by **guarding the roots against rot**, not by feeding the plant. The best-supported are a few fungi and bacteria (Trichoderma, Gliocladium, Bacillus, Streptomyces) that crowd out or attack the bugs behind Pythium and Fusarium root rot [1][2][3][4]. Mycorrhizae help mainly in poor soil and often don't take at all [10]. "Feed your plant" microbe blends have the weakest evidence in a well-fed room [8]. In the founder's words: use them "within reason. Some really do help keep root rot and whatnot away, but not in the way many think or are told, and the good ones may surprise you." (founder's field experience) [11]

> **Greenleaf says:** The good bottles are bodyguards, not chefs. They protect the roots; your nutrient solution does the feeding.

## How do the good ones actually work?

By protecting roots, four ways. *Established (plant pathology).*

1. **Crowding out** (competitive exclusion): they colonise the root surface first, leaving less room and food for pathogens [1][2].
2. **Chemical weapons** (antibiosis): Bacillus species make antifungal lipopeptides and other compounds [2].
3. **Attacking the pathogen** (mycoparasitism): Trichoderma coils around other fungi and digests them [1].
4. **Priming the plant's own defences** (induced systemic resistance) [1][2].

That's why the good ones "surprise" people: a fungus in a bottle protecting roots from other fungi, or a soil bacterium (Streptomyces) that makes antibiotics, isn't what most labels sell.

**What the label says vs what the evidence supports**
- **The label** (Bigger yields, more nutrients)
  - Con: 'Feeds your plant' or 'boosts nutrient uptake'
  - Con: Weakest evidence in a fully fed room
  - Con: Results vary by product and strain
- **The evidence** (Root protection)
  - Pro: Reduced Pythium and Fusarium root rot in greenhouse trials
  - Pro: Some products registered for cannabis in Canada
  - Pro: Works best as [prevention](https://genetixbay.com/knowledge/glossary/cultural-control.md)
  - Bodyguards, not chefs.

## The tier list

Ranked by the strength of evidence for what growers actually need: healthy roots. *Supported; tiers are a GenetixBay summary of the sources.*

| Tier | What | Evidence | Best use |
|---|---|---|---|
| **A** | *Trichoderma harzianum* | Suppresses Pythium and Fusarium by competition, mycoparasitism and induced resistance [1]; products listed for cannabis in Alberta [6] | Preventive root protection in soil, coco, rockwool |
| **A** | *Gliocladium (Clonostachys) catenulatum* | Reduced Pythium and Fusarium root rot severity in greenhouse rockwool [3]; listed for cannabis in Alberta [6] | Seedlings, clones, rockwool and coco |
| **A** | *Bacillus subtilis / amyloliquefaciens* | Antibiotic lipopeptides and induced resistance against many plant pathogens [2] | [Root zone](https://genetixbay.com/knowledge/glossary/root-zone.md) and reservoir protection |
| **A–** | *Streptomyces griseoviridis* | Reduced Pythium and Fusarium root rot severity in greenhouse rockwool [3] | Root zone protection |
| **B** | Beneficial-microbe reservoir blends | House-preferred approach for [recirculating hydro](https://genetixbay.com/knowledge/glossary/recirculating-system.md); evidence is product-specific (founder's field experience) [11] | RDWC and [DWC](https://genetixbay.com/knowledge/glossary/dwc.md), instead of a half-hearted sterile reservoir |
| **C** | Mycorrhizae (arbuscular) | Raised root length 34% and P content 24% in a cannabis seedling trial [9]; most of 28 commercial products failed to colonise roots [10] | Low-P soil and living soil; little point in fully fed hydro or coco |
| **D** | "Nutrient-booster" microbes (N-fixers, P-solubilisers) | Promising in research, but cannabis data are limited and benefits shrink when the plant is fully fed [8] | Low-input soil experiments |
| **D** | [Compost tea](https://genetixbay.com/knowledge/glossary/compost-tea.md) | Inconsistent disease control, no cannabis trials, food-safety risks with [molasses](https://genetixbay.com/knowledge/glossary/molasses.md) brews (see [does compost tea work?](https://genetixbay.com/knowledge/answers/does-compost-tea-work.md)) | Skip it |

For cannabis specifically, Punja's lab has tested biological control agents against Fusarium damping-off and Pythium root and crown rot on cannabis plants [5], after documenting how these pathogens attack hydroponic cannabis [7].

**The tier list in one glance.** A: Trichoderma, Gliocladium, Bacillus (Root-rot protection); B: Beneficial reservoir blends (House-preferred in hydro); C: Mycorrhizae (Low-P soil only); D: 'Nutrient boosters', compost tea (Weakest evidence). Source: Tier table above [1][2][3][6][8][9][10]; house preference [11].

## Rules for using them well

- **Prevention, not cure.** Start at planting or from the first fill; they don't rescue an established infection [1][3].
- **Don't mix with sterilants.** Hydrogen peroxide and chlorine kill the good with the bad. House position: a beneficial-microbe reservoir is preferred, but a sterile reservoir is valid if you commit fully (founder's field experience) [11].
- **Fix the basics first.** Root rot loves warm, low-oxygen water: keep reservoirs cool and well aerated (see [sanitation and prevention](https://genetixbay.com/knowledge/diseases/sanitation-and-prevention.md)).
- **Use registered products** where your jurisdiction requires it for cannabis [6].
- **Don't feed the reservoir sugar** (see [molasses and sugars](https://genetixbay.com/knowledge/nutrients/molasses-and-sugars.md)).

## Common mistakes

- Buying microbes to "feed" a plant that's already fully fed.
- Adding microbes and hydrogen peroxide to the same reservoir.
- Expecting a bottle to cure established root rot.
- Paying extra for mycorrhizae in coco or hydro.

## Sources

1. Harman GE. 2006. Overview of mechanisms and uses of Trichoderma spp. Phytopathology 96(2):190-194. https://doi.org/10.1094/PHYTO-96-0190
2. Fira D, Dimkić I, Berić T, Lozo J, Stanković S. 2018. Biological control of plant pathogens by Bacillus species. Journal of Biotechnology 285:44-55. https://doi.org/10.1016/j.jbiotec.2018.07.044
3. Rose S, Yip CY, Punja ZK. 2004. Biological control of Fusarium and Pythium root rots on greenhouse cucumbers grown in rockwool. Acta Horticulturae 635:73-78. https://doi.org/10.17660/ActaHortic.2004.635.9
4. Punja ZK, Yip R. 2003. Biological control of damping-off and root rot caused by Pythium aphanidermatum on greenhouse cucumbers. Canadian Journal of Plant Pathology 25(4):411-417. https://doi.org/10.1080/07060660309507098
5. Scott C, Punja ZK. 2023. Biological control of Fusarium oxysporum causing damping-off and Pythium myriotylum causing root and crown rot on cannabis (Cannabis sativa L.) plants. Canadian Journal of Plant Pathology 45:238-252. https://doi.org/10.1080/07060661.2023.2172082
6. Government of Alberta. Registered cannabis pesticides (biofungicides including Gliocladium catenulatum J1446 and Trichoderma harzianum products listed for Pythium and Fusarium). https://www.alberta.ca/registered-cannabis-pesticides
7. Punja ZK, Rodriguez G. 2018. Fusarium and Pythium species infecting roots of hydroponically grown marijuana (Cannabis sativa L.) plants. Canadian Journal of Plant Pathology 40(4):498-513. https://doi.org/10.1080/07060661.2018.1535466
8. Lyu D, Backer R, Robinson WG, Smith DL. 2019. Plant growth-promoting rhizobacteria for cannabis production: yield, cannabinoid profile and disease resistance. Frontiers in Microbiology 10:1761. https://doi.org/10.3389/fmicb.2019.01761
9. Kakabouki I, Mavroeidis A, Tataridas A, et al. 2021. Effect of Rhizophagus irregularis on growth and quality of Cannabis sativa seedlings. Plants 10(7):1333. https://doi.org/10.3390/plants10071333
10. Salomon MJ, Demarmels R, Watts-Williams SJ, et al. 2022. Global evaluation of commercial arbuscular mycorrhizal inoculants under greenhouse and field conditions. Applied Soil Ecology 169:104225. https://doi.org/10.1016/j.apsoil.2021.104225
11. GenetixBay founder. Field experience (first-hand account; GenetixBay house position).