On the shelves in your local garden supply store, you may have noticed products labeled “mycorrhizal fungi” and wondered what their purpose is and whether they would benefit your garden.
They have been touted as the cure to what ails our plants, but the research is much more nuanced. There is still more evidence needed to clarify the role that mycorrhizae play in our gardens, forests, and the food we eat, but what we know so far is that they are fascinating and important.
Mycorrhizal fungi grow on and around plant roots, forming a symbiotic relationship with plants that facilitates the transportation of nutrients and water to the host plants. Networks of mycorrhizal fungi exist in most natural settings, supporting a wide variety of plants. This is not surprising since fungi in general are one of the largest groups of life on Earth and have colonized virtually every niche of the planet.
Fungi are eukaryotic organisms, a group that includes yeasts and molds, as well as our familiar mushrooms. Fungi most likely evolved over 1.5 billion years ago and started colonizing land during the Cambrian Period, around 570 million years ago. The most interesting thing about mycorrhizal fungi is that they co-evolved with plants. They have been with us since before there was an “us.”
So, what does this ancient organism have to do with you and your garden today? A lot, actually! Soil devoid of mycorrhizae cannot fully support the growth of plants that are vigorous, disease-resistant and can handle changes in weather such as drought. We need to consider what gardening practices encourage the growth and continued survival of these fungal networks. This may be the hard part, but interestingly, a large part of the task is to do less.
The first piece to understand is the specific benefits mycorrhizae provide to the garden:
1. Because mycorrhizae increase nutrient and water uptake in plants, these plants establish faster, grow bigger and survive longer than plants without mycorrhizae.
2. Mycorrhizae improve soil aggregation and stability, helping prevent erosion and allowing water to seep in more deeply.
3. Healthier plants are more resistant to environmental stress, pests, and diseases, especially root pathogens such as Verticillium and nematodes.
4. Mycorrhizae colonized plants have increased tolerance to drought, salt, and heavy metals such as zinc and lead. Mycorrhizae can help prevent uptake of these toxic minerals from soil and inhibit their movement from the roots to the shoots.
5. Mycorrhizal networks can reduce excess soil nutrients from seeping into aquatic ecosystems, improving waterway health.
The second piece to understand is how mycorrhizae grow in partnership with plants. This is a natural process that rewards those who do less. Mycorrhizal spores lie dormant in coarse organic matter near the soil surface and in the soil itself. Roots of plants under nutritional stress release specific chemical cues that stimulate spore germination. Once the spores have germinated, they colonize the plant roots and then the “magic” can happen.
The third piece to consider is how certain actions in your garden can inhibit mycorrhizae growth:
1. The most damaging threat to mycorrhizal health is the use of unnecessary fertilizers, especially those containing phosphate.
2. Any activity that destroys soil structure, including excessive tilling and cultivation, will also decrease the formation and health of mycorrhizal networks.
3. Overuse of fungicides to remove unwanted fungi from gardens and yards also kills beneficial fungi – essentially, if you have visible fungi in your lawn or garden, leave them!
4. Topsoil removal during construction is extremely damaging, as much of the inoculum and organic material is eliminated. Construction also compacts the soil and reduces oxygen, lowering oxygen-dependent mycorrhizal activity.
I am sure that, like me, you have seen many mycorrhizal products for sale that you can add to your soil. There has been some success in inoculating sterilized container media and in repopulating soils that have been fumigated. However, studies on gardens and landscapes have found that mycorrhizal amendments are generally ineffective and unnecessary.
Since most soils have at least some mycorrhizal spores already in them, if you foster the right conditions, they will continue to grow and colonize. Use a handful of soil from an existing bed to colonize a new bed. Save your money at the garden supply store!
Finally, what can we do to increase mycorrhizal communities and reap the benefits in our gardens?
1. Soil Management
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Decrease or stop rototilling and double-digging, which destroy fungal networks.
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Avoid soil compaction as it decreases pore space and reduces oxygen availability.
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Avoid excessive irrigation as this also reduces soil oxygen levels.
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Apply compost as a top dressing; it will find its way naturally into the soil through water movement and soil fauna activity. Let worms do the work!
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Use natural woody mulches instead of dyed ones. They are less expensive, and sometimes free.
2. Chemical Use
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Avoid using fungicides; use them as a last resort to treat serious fungal diseases.
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Apply fertilizer only when a soil test warrants it. Excessive fertilizer, especially phosphate, damages the mycorrhizal network.
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Include low-growing drought-tolerant ground covers to act as living mulches and avoid bare soil.
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Plant a diverse variety of plants, trees, shrubs, flowers, herbs, and vegetables. Diverse planting encourages mycorrhizae networks.
When you really think about how we can encourage the growth of these invaluable networks in our gardens, you will notice that the key steps actually require less work. I encourage every gardener to consider doing this!
Abby Dowling is a Penn State Master Gardener in Beaver County.
This article originally appeared on Beaver County Times: Mycorrhizal fungi has benefits for soil and plants
