Mycorrhizae inoculants: evidence-based use

The mycorrhizal inoculant market has grown substantially alongside interest in soil biology, and a walk through any garden center now turns up shelf space dedicated to powders and granules promising to "activate your soil" or "supercharge root growth." The science behind mycorrhizae is real and.

The mycorrhizal inoculant market has grown substantially alongside interest in soil biology, and a walk through any garden center now turns up shelf space dedicated to powders and granules promising to "activate your soil" or "supercharge root growth." The science behind mycorrhizae is real and well-established. The science behind most commercial inoculant products is considerably murkier. This guide covers what mycorrhizal fungi actually do, which plants form mycorrhizal associations, what conditions make inoculants beneficial versus useless, and how to read product claims critically.

What mycorrhizal fungi do

Mycorrhiza (from Greek: mykes = fungus, rhiza = root) describes a symbiotic association in which fungal hyphae colonize plant root cells and extend into surrounding soil, effectively expanding the root system's reach by orders of magnitude. Per University of Florida IFAS Extension, a single mycorrhizal plant can have a hyphal network extending 100 times further from the root surface than root hairs alone. This matters for two reasons:

Phosphorus acquisition. Phosphorus moves through soil by diffusion — slowly — and plant roots deplete the immediately surrounding zone rapidly. Fungal hyphae penetrate micropores that roots cannot reach and deliver phosphorus back to the host plant. In exchange, the plant provides 10–20% of its photosynthetically fixed carbon to feed the fungus.

Water and micronutrient uptake. Hyphal networks also improve uptake of zinc, copper, and water, particularly under drought stress.