Mycorrhizae

There’s a fungus among us!

The root systems of nearly all your plants (except those in the cabbage family) are infected with a tiny fungus called mycorrhizae. Now, before you panic, you need to understand that this is a good thing!

Beech tree root with mycorrhizae (Katrin Schulz) Pixabay

Mycorrhizae means ‘root fungus’. These microorganisms have evolved in a symbiotic, or mutually beneficial, relationship with plant roots. Just as rhizobium bacteria help plants ‘fix’ atmospheric nitrogen into a form usable by plants, mycorrhizae are important part of the soil food web and critical to plant health.

Mutually beneficial arrangements

Tiny root hairs give the mycorrhizae sugars, created through photosynthesis, B vitamins, and other important resources in exchange for water, hormones and minerals found in the soil. This is how plants absorb soil nutrients. Without these critical elements, plants fail to thrive and they become susceptible to pests and diseases. Plants that host mycorrhizae have access to 50-100 times the nutrients than plants without. This is especially true when it comes to pulling phosphates from the soil.

Types of mycorrhizae

There are several types of mycorrhizae with two major players: those that live mostly on and occasionally inside roots (ectomycorrhizae) and those that “infect” the roots of nearly 80% of all plant species (ednomycorrhizae). These microscopic fungi extend thread-like appendages, called hyphae, into the soil. These are the white threads you see under decomposing wood chips, mulch, and compost. And they are worth their weight in gold!

Mycorrhizae provide far more than a simple trade agreement with your plants. They also:

• improve soil structure
• reduce erosion
• suppress diseases, such as Verticillium wilt
• more resistant to pests, such as nematodes
• improve resilience to harsh environmental conditions, such as drought, soil salinity, and heavy metals
• reduced need for added fertilizers
• reduce run-off and leaching
• improve water quality

Mycorrhizae improve root growth significantly (USDA) Public Domain

You can inoculate your soil with store bought mycorrhizae, but the conditions of temperature, moisture and soil must be exactly correct, or they will simply die off and be a waste of money. In most cases, repopulating soil with purchased mycorrhizae only works in the lab and not in the field. Instead, you can make your soil more hospitable to these mycorrhizae with these tips:

• avoid adding excessive amounts of plant nutrients, particularly phosphates, which inhibit mycorrhizal growth [nutrients should ONLY be added after a soil test indicates a deficiency]
• employ no-dig gardening whenever possible to avoid disturbing mycorrhizal communities
• reduce soil compaction
• avoid over-watering
• top dress the soil with aged compost, rather than digging it in
• mulch with arborist chips, which naturally contain beneficial fungal spores
• avoid using fungicides and bactericides
• increase the biodiversity of your plantings

You can improve the health of containerized plants by tossing them a handful of soil from outside. That soil will contain beneficial mycorrhizae that will help your potted plants thrive.