Mycorrhizal Fungi: The Root Network

By James Wilson · October 8, 2026

What Mycorrhizae Are

Mycorrhizal fungi form symbiotic relationships with 90% of plant species. The fungal hyphae extend far beyond the root zone — effectively multiplying the root surface area by 100-1,000 times. In exchange for sugars from photosynthesis, fungi deliver water and minerals that roots cannot reach alone.

Two Types: Arbuscular and Ectomycorrhizal

Arbuscular mycorrhizae (AM) penetrate root cells and associate with most vegetables, flowers, grasses, and tropical trees. Ectomycorrhizae (ECM) surround roots without penetrating and associate with oaks, pines, birches, and beeches. A garden typically hosts dozens of fungal species simultaneously.

How They Help Plants

Fungal hyphae access phosphorus in soil pores too small for roots. They solubilize minerals locked in rock particles. They connect plants underground, allowing nutrient transfer between species — a dying tree can send carbon to seedlings through mycorrhizal networks. They also trigger systemic disease resistance in connected plants.

Winter Survival of Mycorrhizae

Mycorrhizal networks persist through winter in undisturbed soil. Fungi store carbon in glomalin — a sticky protein that also binds soil particles into aggregates. Tilling destroys hyphal networks, which is why no-till gardens show increasing mycorrhizal colonization year over year.

How to Encourage Mycorrhizae

Avoid synthetic phosphorus fertilizer — high soil P suppresses the symbiosis. Minimize tilling. Plant diverse species — fungal diversity tracks plant diversity. Use living roots year-round through cover crops. Avoid fungicides, which kill mycorrhizae along with pathogens.

Inoculation: Does It Work

Commercial mycorrhizal inoculants can help establish fungi in degraded soils. However, if your soil already has healthy fungal populations, added inoculant may not improve colonization. The best inoculant is undisturbed soil from a healthy forest or meadow edge added to new beds.