“The soil food web that will point the way to many orchard answers quite generously includes us humans within this symbiosis of place.” - Michael Phillips, The Apple Grower
Understanding the Connection Between Soil Fungi and Orchard Health
By Chuck Schembre, Understanding Ag, LLC
All orchard crops –fruit trees, nut crops, grapes and berries– are perennial plants which have developed a strong symbiotic relationship with fungal life, both in the soil and the plant canopy. Without a healthy and diverse microbial community of fungi, perennial crops cannot develop a strong immune system and natural defenses against disease and pest. The physiology of trees, including photosynthesis, the uptake of nutrients, the synthesis of proteins and carbohydrates, and ability to resist disease and pests have evolved in coexistence with the presence of mycorrhizae and saprophytic fungi, among many other soil microbial species.
What may be of most importance is the role of soil fungi, and their role in providing perennial crops many forms of trace elements which are foundational to complete plant nutrition and plant health function. When a tree has complete biological nutrition, meaning it is getting its nutrition from the soil biology, it can efficiently and effectively store carbohydrate reserves into the organs. Abundant carbohydrate reserve storage into all the tree organs (roots, trunk, branches, buds), is critical for the overall survival and resiliency of the tree. This includes resiliency against disease and pests, consistent and strong bud break and pollination, and winter survival as a young tree through severe winter storms. Without a soil teaming with life, trees cannot create and store enough carbohydrates to promote complete tree health and productivity.
Before Understanding AG, LLC, coined and developed the 6-3-4™ regenerative approach, the principles were already proven to be highly successful in perennial crops, through the work of a few pioneering orchardists. In honor of one my most influential mentors, I would like to revisit and give reverence to the work and teachings of the late Michael Phillips, the original teacher of regenerative orcharding. Michael referred to this type of farming as Holistic Orcharding, and he wrote the book The Holistic Orchard. His first book was The Apple Grower, which was one of the first mainstream publications to bring awareness to the orchard as an ecosystem, and the importance of mycorrhizal fungi for tree health. He then wrote the book Mycorrhizal Planet, which is one of the most elaborate books interweaving science, art, and poetry. It is the kind of book anyone with an interest in nature would love to read.
I attended one of Michael’s intensive workshops at the Eco Farm Conference in CA around 2008. Having read The Apple Grower, I was interested in learning how to become a better organic fruit grower and further pursue my love of fruit trees. What I didn’t expect to occur, is that he would send me into a paradigm shift that would forever change my way of looking at agriculture and gardening, for the better. Keep in mind at this time, I already knew about mycorrhizal fungi and had already been an organic and ecological grower for about 4-5 years. As regenerative agriculture in orchards and vineyards progresses into many forms, I continually think about how far ahead Michael was for his time, and how many people skip right over the fundamental understanding of what a tree or vine really needs to achieve optimal health – an abundance and diversity of all types of fungi. This article is as much a homage to Mr. Phillips’ passion to teach about the soil life as it is to introduce the foundation of regenerative orcharding. For the rest of this article, I will refer to orchards and trees, however all the information applies to all perennial fruit and nut crops.
Commercial orchards have entered an era of failing economics, and everywhere I turn, more and more orchards are plagued with disease and pest pressure, eventually left to a perilous economic fate, the orchard trees often ripped out before they reach 20 years of life. They all suffer from ecosystem disfunction and are devoid of soi life. Fungi, often overlooked in larger-scale commercial agriculture, plays a foundational role in building resilient ecosystems and healthy trees which require little to no inputs to produce quality fruit. Let’s dive into how soil fungi contribute to orchard health and the practical ways to foster these symbiotic relationships.
The Role of Soil Fungi in Orchard Ecosystems
Orchard crops—whether fruit trees, nut trees, or vineyards—are perennial plants deeply intertwined with all soil life, and more importantly, fungal life. The genetics of perennial plants have co-evolved with mycorrhizal and saprophytic fungi, forming partnerships that enhance the survival, health, and productivity of each. Without an abundance of soil life, perennial crops cannot survive without significant intervention from humans.
Soil fungi are categorized into two primary species:
- Mycorrhizal Fungi: These fungi form symbiotic relationships with tree roots. Their hyphal networks extend far into the soil, effectively expanding the root system by 100 to 1,000 times. They aid in nutrient and water uptake, particularly minerals like phosphorus, nitrogen, calcium, potassium, and many trace elements critical for plant immune system health and food nutrient density. Mycorrhizal fungi also enhance the soil's structure by producing glomalin, a sticky protein that helps create stable aggregates.
- Saprophytic Fungi: These decomposers are critical for cycling nutrients from the top down, breaking down organic matter such as fallen leaves, deadwood, and other plant residues. In doing so, they recycle nutrients, making them available for smaller soil organisms, such as bacteria, which turn these organic matter sources into plant available nutrients. They also help regulate fungal pathogens, maintaining a balanced microbial community.
Key Benefits of Soil Fungi for Orchards
Healthy populations of soil fungi offer several advantages to orchard systems:
- Enhanced nutrient cycling: Fungi transform unavailable nutrients into plant-accessible forms.
- Improved water uptake: Fungal networks tap into soil moisture, even from deep or distant sources, helping trees thrive in challenging conditions.
- Increased disease resistance: Fungi bolster the tree’s immune system, making it more resistant to pests and pathogens. Without an abundance of fungi, a tree can not develop natural immunity to disease.
- Resilience against weather extremes: Trees with well-established fungal associations store more carbohydrates in their organs, enabling them to better withstand cold winters, droughts, or sudden weather changes.
Mycorrhizal Fungi: The Tree’s Underground Partner
The partnership between trees and mycorrhizal fungi is one of nature’s most profound collaborations. These fungi colonize tree roots, forming a network that not only enhances nutrient and water uptake but also interconnects trees in an underground "internet" of shared resources and communication.
Key functions of mycorrhizal fungi include:
- Nutrient mining: Hyphal networks penetrate deep into the soil, extracting minerals and trace elements that roots alone cannot access.
- Soil carbon cycle: Mycorrhizae contribute to carbon cycling and storage, which supports broader soil health.
- Disease suppression: By forming a protective barrier around roots, mycorrhizal fungi reduce the risk of root-borne diseases. Their ability to provide trace elements provide the proper nutrition to synthesize secondary metabolites, or in other words, “super foods” for the tree.
Saprophytic Fungi: Nature’s Recyclers
Saprophytic fungi are equally vital, particularly for their role in decomposition. They break down high lignin organic matter into simpler compounds, facilitating the nutrient cycle. Their presence in the tree canopy (phyllosphere) and soil surface regulates disease pathogens. In fact, most of the major fungal diseases in agriculture are saprophytic which have become antagonistic because the ecosystem is out of balance. A diversity and abundance of saprophytic fungi can keep the “bad guys” in check.
Because fungicides are designed to kill saprophytic species, these fungi are sensitive to fungicides, which means conventional practices often suppress their populations, reducing the orchard's natural ability to manage diseases and pests.
Building Fungal Communities in Orchards
To regenerate fungal populations in commercial orchards, it’s essential to follow the Six Principles of Soil Health in order build an abundance of what Michael Phillips termed, “Fungal Foods.” We also need a diversity of fungal foods to support biological diversity. How do we build a diverse buffet of fungal foods free of charge? The answer lies in maximizing photosynthesis across the field, starting with the orchard floor.
Photosynthesis is responsible for creating plant biomass, using nature’s free resources, the sun, water, and soil minerals. The plant biomass built in the orchard becomes the source for pumping carbon into the soil as sugar-rich root exudates (mycorrhizal food) and as the above ground material which will decompose into the soil surface (saprophytic foods), feeding the soil microorganisms and the fungi.
Although Michael Phillips is one of the greatest regenerative teachers and practitioners of all time, and my personal guru, he likely did not emphasize the importance of field-scale photosynthesis enough. He stressed the importance of keeping the soil covered with a diversity of plants, which essentially results in maximizing photosynthesis. He emphasized feeding fungi through applications of mulches, compost, and managing leaf litter, which he termed “fungal foods or fungal duff.” In my work, I have embraced the term “fungal foods,” and have focused on how nature most effectively feeds soil fungi. I have found that by maximizing photosynthesis on the orchard or vineyard floor we will create an abundant diversity of plant biomass, organic matter or high--carbon inputs, constantly flowing into the soil. Once we create a self-perpetuating farming system, these “fungal food” inputs never stop flowing, and the soil fungi provide their greatest ecosystem services to your farm and crop productivity.
Example of increasing “fungal foods” around the base of the tree. One of the most critical needs for tree health is increasing soil armor with a continuous flow of decomposing organic matter from the orchard floor vegetation, tree leaf litter, and applied mulches.
Photo Left: Example of increasing litter and duff around the tree base. This grower as applied various sources of mulch, including rice hulls and wood chips.
Photo Right: Example of allowing vegetation to grow around the tree in the early season. Leaf litter has accumulated around the base of the tree. The combination of plant diversity and leaf litter as created very healthy levels of saprophytic fungi levels.
Conclusion: The Journey to a Regenerative Orchard Ecosystem
Tree crops and other perennial crops should be developing a strong symbiosis with fungi immediately at the beginning of their life to naturally develop optimal health. Because most orchards are very depleted in soil fungi, and the trees lack the natural ability to defend themselves, it is important to understand how to transition your orchards while mitigating the risk of crop failure. Although soil fungi can repopulate very quickly, building and sustaining fungal communities to create plant and ecosystem resilience is not a quick fix; it’s a journey that requires commitment and a shift in mindset.
In the next part of this series, we’ll explore how to implement UA’s 6-3-4ä principles and rules, and the specific regenerative practices that orchardists can implement to create thriving, fungal soils and ultimately improve farm economics.