Mycorrhizal fungi are invaluable partners for plants, forming symbiotic relationships with roots that enhance growth, nutrient uptake, and overall resilience. By increasing the mycorrhizal fungi in your garden soil, you can help your plants thrive! In this guide, I’ll explain what mycorrhizal fungi are, why they are so beneficial, and give tips on growing mycorrhizal fungi levels through organic gardening practices.
What Are Mycorrhizal Fungi?
Mycorrhizal fungi form mutually beneficial relationships with plant roots. The word “mycorrhiza” literally means “fungus root” in Greek. The fungi colonize the root cells of host plants, receiving carbohydrates in return for increasing the plant’s access to water, nutrients, and soil minerals.
There are several types of mycorrhizal fungi including
- Arbuscular mycorrhizal fungi (AMF) – the most common; they penetrate root cells and form arbuscules for nutrient exchange
- Ectomycorrhizal fungi – form a sheath around root tips, common with trees
- Ericoid mycorrhizal fungi – associate with heathers and heaths
- Orchid mycorrhizal fungi – provide nutrients to orchids with very small seeds
The Benefits of Mycorrhizal Fungi
Mycorrhizal fungi increase the effective surface area of roots, providing improved:
- Nutrient absorption – especially immobile nutrients like phosphorus, zinc, and copper
- Drought tolerance and disease resistance
- Soil aggregation and structure
- Resistance to soil toxins and pollutants
Plants can use less chemical fertilizer if they have mycorrhizal fungi on their roots. This makes the plants more sustainable and increases their yields.
How Mycorrhizal Fungi Help Plants
Mycorrhizal fungi improve plant growth through:
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Increased Nutrient Absorption – The fungal hyphae explore and access more soil and minerals.
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Improved Water Uptake – The extra-radical hyphae bridge gaps between soil particles, improving absorption.
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Disease Protection: The fungi act as secondary roots, keeping pathogens from getting to the roots directly. They may also induce systemic resistance.
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Improved Soil Structure – Fungal hyphae and the glycoprotein glomalin contribute to stable soil aggregates.
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Pollutant Protection – Mycorrhizal fungi can metabolize certain pollutants and reduce toxicity to plants.
Ways to Increase Mycorrhizal Fungi
Here are some methods to increase mycorrhizal fungi in garden soil:
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Avoid excessive tillage – Repeated tilling damages fragile fungal networks.
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Grow mycorrhizal host plants – Grow tomatoes, peppers, clover and more. Avoid brassicas.
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Apply compost – Contains fungi spores and mycelium to spread to plant roots.
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Top dress with organic matter – Aged manure, leaf litter, leaf mold harbor mycorrhizal fungi.
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Interplant with nurse crops – Clover roots harbor fungi to colonize nearby plants.
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Inoculate with commercial mycorrhizae – Add concentrated inoculants when planting.
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Reduce soil disturbance – Limit tillage and use cover cropping for healthy fungal networks.
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Eliminate synthetic fertilizers/fungicides – These harm beneficial fungi, prioritize organic practices.
Making DIY Mycorrhizal Fungi Inoculant
Make homemade inoculant by:
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Collecting soil samples from healthy, undisturbed areas containing abundant mycorrhizal fungi.
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Mixing soil samples with vermiculite, perlite, peat moss or compost to increase volume at a 1:3/4 ratio.
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Planting mustard, millet or sorghum seeds in the inoculant blend and allowing 4-6 weeks growth until established.
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Cutting shoots, chopping colonized roots into the inoculant medium.
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Letting the inoculant rest several more weeks for increased spore formation.
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Applying the finished product by mixing into planting holes or seed rows at 1-2 tablespoons per hole/foot of row.
Homemade inoculant works best when using live cultures immediately. You can also propagate specific strains with lab methods. This simple soil-based method harnesses beneficial native fungi.
Adding mycorrhizal fungi gives plants an upgraded root system! Follow organic practices that protect and promote mycorrhizal fungi to enhance your garden’s health without heavy chemical inputs. Implement some of these methods this season – your plants will thank you!
On-farm production of inoculum
The goal of our research was to develop an on-farm inoculum production system that generated a potent, effective, species rich inoculum that was inexpensive to produce. By avoiding the associated costs of commercially produced inoculum, on-farm production makes the economic and environmental benefits of AM fungi available to a larger number of farmers.
Even though big increases in yield depend on the year, crop, and cultivar, our system was made to be used regularly. If farmers use the cheap system every year, they will be able to make money when mycorrhizae improve conditions that hurt yields. But if inoculum doesn’t affect yields, the system won’t be a drain on the economy. We are targeting vegetable farmers who produce their own seedlings on site for later outplanting to the field, so adapting their current systems to produce colonized seedlings is simple. Although large scale, direct application of inoculum to fields is possible, the return on investment for crops such as field corn and soybean is too low to make inoculum application economically attractive.
On the farm, “host plant” seedlings are first put into black plastic bags that are full of a mix of compost, vermiculite, and local field soil. AM fungi present in the field soil colonize the root of the host plants and over the growing season, the mycorrhizae proliferate as the host plants grow. Once the host is killed by frost, the mycorrhizae will naturally spend the winter in the compost and vermiculite mix. In the spring, the inoculum will be ready to use. Most of the system has been tested through experiments to find the best ways to get the most production out of it, from the type of compost used to the rate of dilution. The end result is a system that can make hundreds of propagules per cubic centimeter and has successfully spread all AM fungi that were tested. In one trial, 465 propagules cm-3 were produced, a 7000 fold increase relative to the concentration in the field soil that was initially added to the bag.
Here we walk through the process step by step and analyze the details that will make your on-farm system a success. Citations are provided to direct you to articles for further reading (see the end of this article for all reference information).
Choosing a host plant
The most important factor in choosing a host plant is selecting a plant that supports mycorrhiza growth. Crops such as spinach, sugar beet, lupine and members of the mustard family do not form a symbiosis with AM fungi. A dependable host for the majority of AM fungi species, bahiagrass (Paspalum notatum Flugge) has been used extensively. Additionally, to prevent the spread of pathogens, the host plant should be from a different family than the inoculated crop. Due to the fact that the inoculum system targets vegetable producers, bahiagrass, a member of the grass family, is an ideal general host. Finally, as a tropical plant, bahiagrass will be frost killed and will not become a weed pest in the field.
As of yet, bahiagrass seedlings are not commercially available. In order to use bahiagrass as a host plant, farmers must establish their own seedlings. We simply germinate bahiagrass seeds in either vermiculite or seed starter and transplant the seedlings into conical plastic pots filled with a sand and soil mixture. Taller than the typical greenhouse flat, these conical pots produce seedlings with a long root system. When outplanted into the bags of diluted compost, the long root ball will come into contact with propagules deep in the bag more quickly than would seedlings produced in shallower pots. The sand and soil mixture we use in the conical pots is a 1:3 soil:sand (volume basis) mix that uses sterilized field soil and coarse swimming pool sand. If the bahiagrass seedlings are grown in a typical greenhouse potting medium, we have found that they become iron deficient.
The process of germinating bahiagrass and establishing seedlings is usually started in the greenhouse four months before the last frost date so the plants can be transplanted as soon as possible after the frost. (For a printable timeline and information on where find these materials see our Quick and Easy Guide to On-Farm Mycorrhizae Inoculum Production.)
How to Grow Your Own Mycorrhizal Fungi in Chicken Manure and Wood Shavings
FAQ
How long does it take for mycorrhizal fungi to grow?
Though it varies by plant species, growing protocol, etc. , it generally takes about 8 weeks for benefits to become visible to the grower in comparison trials. Differences may be visible sooner in more stressful growing conditions, as this is when the mycorrhizae can bring the most benefits to the plants.
How do you encourage mycorrhizal fungi?
Encourage mycorrhizal fungi and increase the health of soil and garden with these simple techniques. Reduce tilling. Leave a layer of organic matter on top of the soil. Use native plants. Don’t leave the soil bare.
Can you sprinkle mycorrhizae on top of soil?
Mycorrhizal products are often used by gardeners when sowing seeds, when transplanting, or to inoculate a bed before planting, working them into the top 4-6 inches. Inoculated soils will actually improve year after year, so it’s a sustainable product.
What are the disadvantages of mycorrhizal fungi?
stramonium, positive associations between AM fungi and plant fitness may not be proportional and, that at high colonization densities, mycorrhizae may have detrimental effects, perhaps by competing with plants for nutrients, or by interfering with other essential interactions.