What Is Mycorrhiza
Under every healthy plant is a web of fungal threads called mycelium. These filaments form partnerships with roots known as mycorrhiza. They’ve existed since plants first grew on land.
The fungus gathers water and nutrients (especially phosphorus) from beyond the plant’s root zone. In return, the plant gives the fungus sugars produced through photosynthesis. It’s a complex trade system that strengthens both partners.
Mycorrhizal fungi also help plants tolerate stress, resist disease, and maintain stable growth. I came back to this idea while reading Entangled Life by Merlin Sheldrake this fall. It’s a good reminder of the incredible interconnectedness of all life—and how much fungi influence the world around us, even though they are rarely seen or discussed. They’ve always been central to plant life, and by extension, to herbal medicine.
How Fungi Change Plant Chemistry
When plants form mycorrhizal relationships, their chemistry changes. The exchange of nutrients and stress signals affects the production of the compounds that give herbs their color, scent, and medicinal activity.
A 2023 meta-analysis in Frontiers in Plant Science reviewed dozens of studies and found that plants inoculated with arbuscular mycorrhizal fungi (AMF) had an average 27% increase in active compounds. Flavonoids, terpenes, and phenolic compounds all rose significantly.
- St. John’s wort grown with AMF produced higher levels of hypericin and pseudohypericin.
- Echinacea showed greater concentrations of caffeic acid derivatives.
- Peppermint produced more essential oil.
These differences occur because mycorrhizal fungi alter nutrient uptake and stress signaling. Plants in these partnerships invest more energy in chemical defenses and protective compounds—what we often call “medicine.”
Wild vs. Cultivated
In the wild, herbs grow within living fungal networks, sharing space with other plants, microbes, and decomposers. This competition and balance encourage complex chemistry.
In gardens, tilling, bare soil, and synthetic fertilizers often break these networks. High nutrient levels provided by external fertilizers (synthetic or not) make plants less reliant on fungi, weakening the relationship over time.
This is one reason wild-harvested plants often test higher in active constituents than cultivated ones. The goal in gardening isn’t to copy wild conditions exactly, but to recreate the underground balance that makes wild plants strong.
How to Support Mycorrhizal Life in the Garden
1. Keep Living Roots in the Soil
Plant cover crops or perennials so roots are present year-round. This feeds the fungal community and keeps it active.
2. Avoid Deep Tilling
Tilling breaks fungal threads that take months to rebuild. No-till gardening allows networks to stay connected.
3. Add Mycorrhizal Inoculants
For small gardens, inoculants with species like Rhizophagus irregularis can help reestablish partnerships. Apply directly to roots during planting.
4. Use Compost Instead of High-Phosphate Fertilizers
Compost releases nutrients slowly and supports microbes. High-phosphate fertilizers stop plants from forming fungal partnerships because phosphorus becomes too easily available.
5. Grow Diverse Plants Together
Different root types support different fungal species. Planting a mix of herbs and companions helps maintain balance and deters harmful fungi.
When Fungi Go Wrong
Not all fungi help plants. Pathogenic fungi such as Fusarium and Pythium thrive in compacted or waterlogged soils, attacking roots and blocking nutrient flow.
You can discourage them by keeping soil aerated, avoiding overwatering, and maintaining plant diversity. A diverse natural environment naturally balances out pathogenic species. Compost and mulch support beneficial microbes that outcompete pathogens—a balanced soil community is the best defense against root disease.
In large monoculture systems, stressed plants and disturbed soil create the perfect terrain for disease to spread. Leaving soil uncolonized by anything invites pathogenic fungi—they occupy the same space and use the same resources. By contrast, mycorrhizae trigger plant defenses that keep pathogens from taking hold. Creating conditions where the good fungi establish before the bad ones is an excellent long-term strategy for organic garden health.
This is also why mycorrhizal inoculants work better in home gardens than in industrial farms. Small-scale systems with minimal tilling, moderate or no fertilizer use, and continuous living roots give fungi time to colonize. In conventional agriculture, high phosphorus inputs and annual tillage destroy fungal networks faster than they can rebuild.
Unfortunately, many commercial inoculants contain inactive spores or mismatched strains, leading to poor results and skepticism about their effectiveness in large-scale agriculture.
What to Look for in Quality Products
- Strain: Rhizophagus irregularis is the most research-supported strain for home gardens, especially the DAOM-197198 isolate with consistent field-trial data.
- Labeling: Choose products that list specific species names.
- Potency: Look for propagule counts above 100,000 per pound.
- Quality control: Ensure proper storage conditions and expiration dates, as many inoculants lose viability due to poor handling.
Conclusion
Healthy soil fungi mean healthier plants. Plants grown with active mycorrhizal partners develop stronger roots, greater stress tolerance, and higher levels of medicinal compounds.
If we want potent herbs, we need to look below the surface. The strength of the plant—and the quality of its medicine—start with the fungi and the health of the soil.
References
- Zubek S., Mielcarek S., Turnau K. Hypericin and pseudohypericin concentrations of Hypericum perforatum L. are enhanced by arbuscular mycorrhizal fungi. Mycorrhiza. 2012; 22(2):149–156. https://pubmed.ncbi.nlm.nih.gov/21626142/
- Vo, Zeng et al. Arbuscular mycorrhizal fungi enhance active ingredients of medicinal plants: global meta-analysis. Frontiers in Plant Science. 2023; 14:1276918. https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2023.1276918/full
- Lima dos Santos E., Lins Falcão E., Silva F.S.B. Mycorrhizal technology as a bio-insumption to produce phenolic compounds of importance to the herbal medicine industry. Research, Society and Development. 2021; 10(2): e54810212856. https://rsdjournal.org/rsd/article/view/12856
