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What are Mycorrhizae in Soil and Why Do they Matter?

Updated: Dec 18, 2019

Mycorrhizae is a term that gardeners may be familiar with. Many garden soil products and amendments boast beneficial mycorrhizae, and there are even starter kits for establishing mycorrhizae in your garden. But what exactly are mycorrhizae in soils, and why, as a gardener, should you care about it?

Mycorrhizae (singular: mycorrhiza) are fungal structures that establish symbiotic relationships between plants and fungi. Mycorrhizae is derived from the Latin “myco” meaning “of fungi” and Greek “rhiza,” meaning “root.” Mycorrhizae are a network of hyphae, or tiny filaments, that connect plants and fungi in the soil. Millions of these microscopic filaments exist in the soil. Although they can’t always be seen with the naked eye, one spoonful of garden soil is estimated to contain more microbial fungi and bacteria than there are people on earth.

About 90% of all plants rely on mycorrhizae to thrive. The mycorrhizal relationship benefits fungi and plants alike. They make nutrients, like carbohydrates and sugars generated through plant photosynthesis, available to underground fungi. Mycorrhizae benefit plants by unlocking nutrients like phosphorus and nitrogen in the soil, creating pathways to the plant’s roots for ready absorption. Beneficial relationships with mycorrhizae are often essential to a plant’s survival. Symbiotic relationships with fungi help to improve a plant’s resilience, production, and longevity.

Two types of mycorrhizae exist—endo-mycorrhizae and ecto-mycorrhizae. About 85% of plants that use mycorrhizae partner with endo-mycorrhizae. Many annuals and perennials utilize endo-mycorrhizae, including vegetables, ornamental plants, flowers, and grasses. About 10% of mycorrhizae-using plants partner with ecto-mycorrhizae, including most hardwood and conifer trees, roses, and some other woody ornamental shrubs.

Endo-mycorrhizae work by penetrating the cell wall of the plant’s roots, establishing hyphae within the cell walls of the root system. These hyphae extend into the soil, accessing and unlocking nutrients that are then readily absorbed by the plant. Endo-mycorrhizae are extremely efficient at delivering phosphorus to plant roots, and they also play a significant role in delivering nitrogen to plants. In exchange, endo-mycorrhizae absorb organic carbon from the plant.

Ecto-mycorrhizae are fungal structures that envelop the plant roots, but do not penetrate the cell walls. They instead surround the cells, creating what is referred to as the Hartig net. Ecto-mycorrhizae is considered the most diverse category of mycorrhizae, partnering with many other fungi to create what is sometimes referred to as the “wood wide web.” These networks allow plants of the same and differing species to send chemical signals to each other. The network of fungi around the roots also serve to create a greater surface area for the root system. The mycorrhizae work more or less as an extension of the root system, absorbing nutrients to exchange with the host plant.

There’s so much more under our feet than just dirt. There is a thriving ecosystem that has co-evolved and created co-dependent relationships for millennia. The next time that you choose a garden soil, choose one that will foster advantageous underground partnerships. All EarthMix® Garden soil mixes, amendments, and composts contain beneficial endo- and ecto-mycorrhizae, along with Humic Acid. Enrich the biodiversity of your garden soil with EarthMix® Garden Products.

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