# Do mycorrhizae help cannabis?

> Mycorrhizae can help cannabis a little, mainly with phosphorus uptake in low-phosphorus soil, but commercial inoculants often don't deliver. In a seedling trial the highest dose raised root length 34% and phosphorus content 24%. A global test of 28 commercial products found most failed to colonise roots. In fully fed hydro or coco, phosphorus is plentiful and colonisation is suppressed, so inoculants are mostly wasted money.

- Canonical: https://genetixbay.com/knowledge/answers/do-mycorrhizae-help.html
- Topic: Nutrients · Type: How-to
- Evidence: Contested · Status: Draft: awaiting expert review
- Full article: [Living soil (no-till, water-only organic growing)](https://genetixbay.com/knowledge/systems/living-soil.md)
- Also asked as: Do mycorrhizal fungi help weed? | Is a root inoculant worth it? | Do myco products work? | Should I add mycorrhizae in hydro or coco? | Mycorrhizae for transplanting
- Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)"

## Short answer

A little, sometimes. [Mycorrhizal fungi](https://genetixbay.com/knowledge/glossary/mycorrhizae.md) colonise cannabis roots and can improve phosphorus uptake, mostly in low-phosphorus soil. In fully fed hydro and [coco](https://genetixbay.com/knowledge/glossary/coco-coir.md) they add little, and many commercial inoculants fail to colonise at all. *Contested*: small cannabis studies, no yield trials in finished plants.

## Why

Arbuscular mycorrhizal fungi extend the root system with fine hyphae and trade phosphorus and some [micronutrients](https://genetixbay.com/knowledge/glossary/micronutrient.md) for plant sugars. The benefit is largest when soil phosphorus is scarce; high soluble phosphorus suppresses colonisation [3].

The cannabis evidence is thin. In a [seedling](https://genetixbay.com/knowledge/glossary/seedling.md) float-system trial, the highest spore dose raised root length 34%, stem [dry weight](https://genetixbay.com/knowledge/glossary/dry-weight.md) 21% and phosphorus content 24%, while root mass and nitrogen were unchanged [1]. That is seedlings, not [harvest weight](https://genetixbay.com/knowledge/glossary/yield.md).

Product quality is the bigger problem. In a global evaluation of 28 commercial inoculants, most failed to colonise host roots [2].

[Living soil](https://genetixbay.com/knowledge/glossary/living-soil.md) is where fungi can earn their keep: no tilling, living roots and minimal disturbance keep soil networks intact [4].

## The numbers

| Situation | Likely benefit | Why |
|---|---|---|
| Living soil, low soluble P | Small, plausible | Native fungi often present already |
| [Bagged soil](https://genetixbay.com/knowledge/glossary/potting-mix.md) with bottled feed | Little | P supplied by feed |
| Coco or [rockwool](https://genetixbay.com/knowledge/glossary/rockwool.md), fed every irrigation | Very little | High P suppresses colonisation |
| [DWC](https://genetixbay.com/knowledge/glossary/dwc.md), [RDWC](https://genetixbay.com/knowledge/glossary/rdwc.md), [NFT](https://genetixbay.com/knowledge/glossary/nft.md) | None to negligible | Constant P, often sanitised |
| Seedlings (one trial) | +34% root length, +24% P content | Highest dose only [1] |

## What to do

1. Decide by system: worth trying only in soil, especially living soil.
2. Buy fresh, dated product; store it cool.
3. Put it in contact with roots at planting or [transplant](https://genetixbay.com/knowledge/glossary/transplanting.md).
4. Keep soluble phosphorus moderate; skip [bloom boosters](https://genetixbay.com/knowledge/glossary/bloom-booster.md).
5. Don't pair it with [peroxide](https://genetixbay.com/knowledge/glossary/hydrogen-peroxide.md) or other root-zone sanitisers.

## Common mistakes

- Paying for inoculants in a high-P hydro feed.
- Sprinkling powder on the surface instead of at the roots.
- Expecting bigger buds rather than, at best, slightly better roots.
- Killing the fungi with chlorinated or peroxide water.

## Related

- Full article: [Living soil](https://genetixbay.com/knowledge/systems/living-soil.md)
- Answers: [compost tea](https://genetixbay.com/knowledge/answers/does-compost-tea-work.md) · [super soil](https://genetixbay.com/knowledge/answers/what-is-super-soil.md)
- Articles: [organic vs mineral](https://genetixbay.com/knowledge/nutrients/organic-vs-mineral.md)
- Terms: [mycorrhizae](https://genetixbay.com/knowledge/glossary/mycorrhizae.md) · [rhizosphere](https://genetixbay.com/knowledge/glossary/rhizosphere.md)

## Follow-up questions

**Do mycorrhizae work in hydro or coco?** Mycorrhizae mostly do not pay their way in hydro or coco. These systems feed phosphorus and other nutrients directly at every irrigation, and high phosphorus supply suppresses mycorrhizal colonisation, so the fungi have little to offer. Root-zone sanitisers such as peroxide kill them as well. Save the money for a calibrated meter.

**Are mycorrhizal inoculants alive when I buy them?** Often not. A global evaluation of 28 commercial arbuscular mycorrhizal products under greenhouse and field conditions found that most failed to colonise host roots. Spores lose viability with storage time and heat. If you buy one, choose a fresh, dated product, keep it cool, and put it in contact with roots at planting rather than on the surface.

**Do mycorrhizae help living soil?** Living soil is the best case for mycorrhizae, because it runs low soluble phosphorus, no sanitisers and no tilling, which lets fungal networks persist between runs. A good compost-rich soil usually already carries native fungi, though, so an inoculant is optional insurance rather than a requirement. There are no controlled cannabis yield trials of inoculated versus uninoculated living soil.

## Sources

1. 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
2. Salomon MJ, Demarmels R, Watts-Williams SJ, McLaughlin MJ, Kafle A, Ketelsen C, Soupir A, Bücking H, Cavagnaro TR, van der Heijden MGA, 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
3. Marschner P (ed.), 2012. Marschner's Mineral Nutrition of Higher Plants, 3rd ed. Academic Press. https://doi.org/10.1016/C2009-0-63043-9
4. USDA Natural Resources Conservation Service. Soil health principles. https://www.nrcs.usda.gov/conservation-basics/natural-resource-concerns/soil/soil-health