Scientists and farmers have uprooted an ancient partnership between plants and fungi. This mutualistic association, called mycorrhizae, has been around for more than 400 million years—basically as soon as plants found their way onto land. More than 90% of plant families form these symbiotic relationships at the root level with fungi.

This sustainable partnership is essential to the circle of life. Plants supply fungi with energy in the form of carbohydrates that are produced during photosynthesis. Fungi are unable to produce their own food from the sun as they lack photosynthetic pigments such as chlorophyll. In return, fungi increase the survival and growth rates of plants by expanding the surface area of roots so more water and nutrients can be absorbed.

The fungal network can transport water and nutrients over large distances and deliver them to the vascular tissues of plants. Roots with this network display an increased uptake of typically insoluble compounds, particularly phosphorus.

The fungi also modify amino acids and carbohydrates for storage, or transfer them to where they are needed, and help plants cope with many environmental issues such as high salinity, drought and pH fluctuations. Mycorrhizal fungi help plants combat harmful pathogens, including the fungus-like genus pythium that causes root rot, by manufacturing and releasing particular enzymes and antibiotics as plants require them.

Individual plants are connected with other plants through this mycorrhizal network, and can even share nutrients, sugars and water. The fungal network is embedded in the vegetative fungal tissues known as mycelium. Multiple species of fungi and plants can be connected through the mycelial network.

This enriches the local community and also extends to interactions with earthworms, bacteria, nematodes and other organisms. For example, nitrogen-fixing rhizobium bacteria in nodules of legumes require mycorrhizal fungi to supply the phosphorus needed for the nitrogen-fixing process. In many instances, fungi harbor nitrogen-fixing bacteria if nitrogen levels in the soil are low.

Types of Mycorrhizal Fungi

There are two main types of mycorrhizal fungi: endomycorrhizal and ectomycorrhizal.

Endomycorrhizal Fungi

Endomycorrhizal fungi are called vesicular-arbuscular mycorrhizae (VAM) in the scientific community. These fungi connect internally with plants by penetrating through the epidermis of root cells. The fungi produce a protein called glomalin that improves soil fertility and also acts as a sealant, sealing the walls of the fungal network so transport is the most efficient it can be. These associations are found in the roots of nearly all flowering plants, and thus are extremely relevant in an indoor gardening discussion.

Ectomycorrhizal Fungi

Ectomycorrhizal fungi­ (EM) form associations with roots without penetrating the root cells. They do this via a hyphal network that surrounds root cells and forms a fungal-root network in the surrounding rhizosphere. The mycelium of certain species of EM can form fruiting bodies that we know as mushrooms or puffballs, which harbor and disperse the reproductive spores of the fungi.

EM only form mycorrhizal associations with 2% of plant species—woody perennials like conifers and oak trees. Most species will only inoculate the roots of the one specific plant species it has evolved with. EM can actually inhibit the growth of endomycorrhizal fungi and compete for resources with other species.

While their role in helping flowering plants is miniscule, ectomycorrhizal fungi are ecologically and economically significant on a global scale, as they are required for the rejuvenation of forest soils and reforestation.

Mycorrhizal Fungi in Indoor Gardens

Mycorrhizal fungi spores are available in many products available in hydroponics shops. The most common forms are the water-soluble powder form and the granular slow-release form. Unfortunately, many products contain species that are irrelevant to flowering plants. These will still be effective overall, but for your indoor plants, try to stick to a mix of purely endomycorrhizal fungi and beneficial bacteria.

A product should also be trichoderma-free. Trichoderma is an antagonistic fungi that benefits plants by controlling disease, but at the expense of inhibiting many species of beneficial fungi. Read company websites and labels, but keep in mind that sometimes a label will not list all the species it contains because of regulations and permits, or they are a trade secret.

Ask a rep at a trade show and contact a company over the phone and ask for the ingredients. Or, best of all, fork out the big bucks for laboratory testing.

One common myth in the indoor gardening industry is that mycorrhizal fungi do not have an application in hydroponics. The truth is that endomycorrhizal fungi do not require soil media to inoculate a plant’s roots.

The fungal associations thrive in hydroponic systems as well as the roots of aquatic plants. It is important to supply high-grade carbohydrates to your nutrient regimen if you are using mycorrhizal fungi, as the fungi require carbohydrates for energy and they obtain them from the plant if there is not a sufficient amount in your feed water. Feed the fungus, or it will take valuable energy from your crop.

Endomycorrhizal fungi also help with the remediation of depleted soils like the peat-based and recycled mixes now common in the indoor gardening industry.

Harnessing the power of mycorrhizal fungi in the garden is a key step in moving forward from the outdated paradigm of global agriculture. Force-feeding our crops with industrial nutrients, herbicides and pesticides is not only unhealthy and unsustainable, it is unnecessary.

With proper gardening techniques and beneficial micro-organisms, we can use less chemicals to get the same results. Thanks to modern research and technology, we are gradually shedding some light on the underground microcosm we walk on.