Fungi in the Garden

What are fungi?

Fungi occupy their own branch on the tree of life. They are not plants, animals, bacteria, or viruses. Some fungi form mushrooms, others do not. Many fungi are multicellular, but some, including yeasts, are single celled. Molds, yeasts, mushrooms, mildews, truffles, and toadstools are all familiar examples of fungi! 

What makes fungi unique is how they eat. Fungi eat through a system of external digestion, meaning they release digestive enzymes into their environment to break down the food around them. Fungal digestion is performed by the mycelium, a root-like structure unique to fungi (if you’ve ever seen white webbing growing on a wood chip, that’s mycelium). This is different from plants, which use photosynthesis to create food, and animals, which internally digest their food.

What do fungi do in nature?

To understand how working with fungi can help us in the garden, we can start by looking at the ecological roles that fungi play in a forest. 

The four main ecological groups of fungi are: 

• saprophytic
•  mycorrhizal
• endophytic
•  parasitic

Saprophytic fungi (also called saprobic) are decomposers. They break down dead organic matter (dead plants, leaves, pine needles, wood, dead animals, etc). This decomposition performed by fungi is critical for cycling nutrients back into the ecosystem. An example of a saprophytic fungus native to our region is the aspen oyster mushroom.

Mycorrhizal fungi are root-associating fungi that live in the soil. (Myco means fungus and rhizo means root!). These fungi have a variety of strategies for physically attaching themselves to plant roots. The plant provides the fungus with the carbon it has photosynthesized in exchange for the fungus providing the plant with other nutrients, water, and medicine.  A mycorrhizal fungus loved by Utahns is Boletus edulis, aka the porcini.

In addition to providing this network of support, one type of mycorrhizal fungi called arbuscular mycorrhizal fungi (we will just call them AMF for simplicity’s sake) create an organic glue called glomalin that binds soil together. Without glomalin, soil becomes compacted and struggles to hold onto nutrients, water, and aerobic pockets (i.e. the air needed for soil biology to breathe). Simply put, the continuous production of glomalin by AMF is needed to build soil structure, and soil structure is needed for healthy plant life.

Endophytic fungi live inside of the plant partner and provide the plant with a variety of benefits, which can include the production of insect deterring compounds and the ability to grow bigger roots and shoots. We can't see endophytes, but they are present in all healthy crops.

Parasitic fungi colonize a living host and eventually kill it. They are a natural part of forest ecosystems and perform very important biological functions. The honey mushroom in Oregon is an example of this. However, when we see parasitic fungi in our garden, they are usually a sign of poor soil and plant health.

What does fungal health look like in the garden?

Most problems that we see in the garden are a result of poor soil health. 

Signs of poor soil health include:

• yellowing of plants (indicating the plant’s inability to receive nutrients)
• browning of leaves (fertilizer damage)
• excessive pests (poor endophytic and mycorrhizal health)
• compacted soil (lack of beneficial soil microbes)
• excessive weeds (lack of soil fungi)

Healthy soil is alive, and the soil biology is what produces healthy plants. As a rule of thumb, we want to facilitate the health of saprophytic, endophytic, and mycorrhizal fungi.  When these populations are healthy, there is not as much opportunity for parasitic fungi.  

Mushrooms that pop up in our garden are usually mycorrhizal or saprophytic. These are typically beneficial, along with the many other mycorrhizal and endophytic fungi that we can not see.  Visible fungal infections on our plants (as opposed to on decaying matter or attached to plant roots) can be an indication of a parasitic fungus (think mildews and blights).

Learn more about healthy soil with local soil expert Paul Grossl here!

What agricultural practices harm fungi?

Unfortunately, many of the practices used in industrial agriculture and even some of the methods we use on small farms or home gardens can be detrimental to fungal health and diversity. 

Tilling is the act of physically churning the soil, usually done with the intention of preparing new ground for cultivation, aerating the soil, or clearing weeds. While it can provide some instant gratification for some of these goals, its long-term effects are very damaging to fungi. Mycorrhizal fungi are obligate symbionts, meaning they cannot live without an attachment to plant roots. When we till our plants, we kill our plants and our fungi. This means we no longer have AMF, which halts the production of glomalin, and ultimately leads to low quality, compacted soil. To compensate for this, we then add excessive fertilizers which often end up in rivers and lakes causing eutrophication (excessive nutrients that harm aquatic life). 

Monocropping is the practice of planting one crop over large areas of land. This limits the type of soil biology that will grow there and leaves the crop susceptible to disease. Intercropping a variety of plants facilitates fungal diversity and puts your cultivated ecosystem in a better position to fight off disease and pests. 

Fungicides, even copper fungicides approved for organic agriculture, tend to kill a wide range of fungi outside of their target. If we are facilitating healthy soil biology, we shouldn’t need fungicides.

How can we take care of our soil fungi?

The first step towards improving soil fungi is to change your mindset from focusing on the plants to focusing on the soil.   If we nurture the soil, the soil will then nurture the crops. 

An important thing to remember is that improving fungal growth takes time.  There aren’t any quick fixes, so patience is key!

There are a few key ways that we can start supporting fungi in our gardens:

• Transition to a no-till system
• Think about what you’re adding to your garden
• Think about what you’re planting and where

Transition to a no-till system

The debate to till or not to till has been around a very long time.  But if we are focusing on building a better fungal network in our soil, not tilling will help.  As you build your soil biology, you will have less weeds and better soil structure. Be patient with the transition. 

Think about what you’re adding to your garden

If we focus on feeding the biology, the biology will feed our plants. Soil organic matter (brown organic matter high in carbon like leaves, pine needles, and straw are good options, as opposed to high nitrogen organic matter like food scraps), compost, compost tea, humic acids, (an amendment that can be found at most garden centers) and worm castings are all excellent options. Liquid and pellet fertilizers tend to inhibit fungal growth.

Think about what you’re planting and where

Cover cropping is an excellent alternative to tilling, and there are even low growing cover crops that can be mowed short or planted directly into. Others may require crimping or killing off with a covering. We can also use soil organic matter (mentioned above) as mulching to slow down weeds and jump start nutrient cycling.

Some plants are more likely to form mycorrhizal relationships than others. As a general guideline, it is best to interplant and rotate brassicas (like cabbage, mustard, and broccoli) and chenopods (like spinach, amaranth, and beets).  These plants are not known to form mycorrhizal bonds with soil fungi as prolifically as crops from other plant families.

Learn more about vermicoposting with Cynthia Strigham here!

In Summary

There is a lot that could be said about this topic and so much that we still have to learn. The takeaway is that fungi are keystone ecological species in both natural and cultivated ecosystems. Hopefully now you have some ideas for how to facilitate fungal well-being!

If you live in Utah and have a home garden you want to show off, click here!